ucla mse104 chapter 1
DESCRIPTION
UCLA Materials Science 104 - Science of Engineering Materials, Chapter 1TRANSCRIPT
Chapter 1 - 1
MSE 104 Introduction to
Materials Science amp Engineering Course Objective Introduce fundamental concepts in Materials
Science and Engineering
You will learn about bull material structure
bull how structure dictates properties
bull how processing can change structure
This course will help you to
bull use materials properly
bull realize new design opportunities with materials
bull select the appropriate materials for engineering
applications
Chapter 1 - 2
Chapter 1 - Introduction bull What is materials science materials engineering
Chapter 1 - 3
ex hardness vs structure of steel bull Properties depend on structure
Data obtained from Figs 1030(a)
and 1032 with 4 wt C composition
and from Fig 1114 and associated
discussion Callister amp Rethwisch 8e
Micrographs adapted from (a) Fig
1019 (b) Fig 930(c) Fig 1033
and (d) Fig 1021 Callister amp
Rethwisch 8e
ex structure vs cooling rate of steel bull Processing can change structure
Structure Processing amp Properties
Hard
ness (
BH
N)
Cooling Rate (ordmCs)
100
2 00
3 00
4 00
5 00
6 00
001 01 1 10 100 1000
(d)
30 mm (c)
4 mm
(b)
30 mm
(a)
30 mm
Chapter 1 - 4
Classes of Engineered Materials bull Metals
ndash High thermal amp electrical conductivity
ndash Opaque reflective strong ductile
bull Polymersplastics Covalent bonding sharing of ersquos
ndash Thermal amp electrical insulators
ndash Optically translucent or transparent
ndash Soft ductile low strength low density
bull Ceramics ionic bonding (refractory) ndash compounds of metallic
amp non-metallic elements (oxides carbides nitrides sulfides)
ndash Non-conducting (insulators)
ndash Brittle glassy inelastic
bull Semiconductors covalent Mixed (ionic) ndash elements (silicon
germanium) or compounds of metallic amp non-metallic elements (arsenides phosphides nitrides)
ndash Engineered Conduction
ndash Brittle inelastic
Chapter 1 - 5
1 Pick Application Determine required Properties
Processing changes structure and overall shape
ex casting sintering vapor deposition doping
forming joining annealing
Properties mechanical electrical thermal optical
corrosive
Material structure composition
2 Properties Identify candidate Material(s)
3 Material Identify required Processing
The Materials Selection Process
Chapter 1 - 6
ELECTRICAL
bull Electrical Resistivity of Copper
bull Adding ldquoimpurityrdquo atoms to Cu (Cu-Ni alloy) increases resistivity
bull Deforming Cu increases resistivity
Adapted from Fig 188 Callister amp
Rethwisch 8e (Fig 188 adapted
from JO Linde Ann Physik 5 219
(1932) and CA Wert and RM
Thomson Physics of Solids 2nd
edition McGraw-Hill Company New
York 1970)
T (ordmC) -200 -100 0
1
2
3
4
5
6
Resis
tivity
r
(10
-8 O
hm
-m)
0
Chapter 1 - 7
THERMAL bull Space Shuttle Tiles -- Silica fiber insulation
offers low heat conduction
bull Thermal Conductivity
of Copper -- It decreases when
you add zinc
Adapted from
Fig 194W Callister
6e (Courtesy of
Lockheed Aerospace
Ceramics Systems
Sunnyvale CA)
(Note W denotes fig
is on CD-ROM)
Adapted from Fig 194 Callister amp Rethwisch
8e (Fig 194 is adapted from Metals Handbook
Properties and Selection Nonferrous alloys and
Pure Metals Vol 2 9th ed H Baker
(Managing Editor) American Society for Metals
1979 p 315)
Composition (wt Zinc) T
herm
al C
ond
uctivity
(Wm
-K)
400
300
200
100
0 0 10 20 30 40
100 mm
Adapted from chapter-
opening photograph
Chapter 17 Callister amp
Rethwisch 3e (Courtesy
of Lockheed
Missiles and Space
Company Inc)
Chapter 1 - 8
bull Transmittance -- Aluminum oxide may be transparent translucent or
opaque depending on the material structure
Adapted from Fig 12
Callister amp Rethwisch 8e
(Specimen preparation
PA Lessing photo by S
Tanner)
single crystal
polycrystal
low porosity
polycrystal
high porosity
OPTICAL
Chapter 1 - 9
bull Use the right material for the job
bull Understand the relation among properties
structure processing and performance
bull Recognize new design opportunities offered
by materials selection
Course Goals
SUMMARY
Chapter 1 - 10
ISSUES TO ADDRESS
bull What promotes bonding
bull What types of bonds are there
bull What properties are inferred from bonding
Chapter 2 Atomic Structure amp
Interatomic Bonding
Chapter 1 - 11
Atomic Structure
bull Atom ndash electrons ndash 911 x 10-31 kg protons neutrons
bull Atomic number = of protons in nucleus of atom = of electrons of neutral species
bull A [=] atomic mass unit = amu = 112 mass of 12C Atomic wt = wt of 6022 x 1023 molecules or atoms
1 amuatom = 1gmol
C 12011 H 1008 etc
167 x 10-27 kg
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 2
Chapter 1 - Introduction bull What is materials science materials engineering
Chapter 1 - 3
ex hardness vs structure of steel bull Properties depend on structure
Data obtained from Figs 1030(a)
and 1032 with 4 wt C composition
and from Fig 1114 and associated
discussion Callister amp Rethwisch 8e
Micrographs adapted from (a) Fig
1019 (b) Fig 930(c) Fig 1033
and (d) Fig 1021 Callister amp
Rethwisch 8e
ex structure vs cooling rate of steel bull Processing can change structure
Structure Processing amp Properties
Hard
ness (
BH
N)
Cooling Rate (ordmCs)
100
2 00
3 00
4 00
5 00
6 00
001 01 1 10 100 1000
(d)
30 mm (c)
4 mm
(b)
30 mm
(a)
30 mm
Chapter 1 - 4
Classes of Engineered Materials bull Metals
ndash High thermal amp electrical conductivity
ndash Opaque reflective strong ductile
bull Polymersplastics Covalent bonding sharing of ersquos
ndash Thermal amp electrical insulators
ndash Optically translucent or transparent
ndash Soft ductile low strength low density
bull Ceramics ionic bonding (refractory) ndash compounds of metallic
amp non-metallic elements (oxides carbides nitrides sulfides)
ndash Non-conducting (insulators)
ndash Brittle glassy inelastic
bull Semiconductors covalent Mixed (ionic) ndash elements (silicon
germanium) or compounds of metallic amp non-metallic elements (arsenides phosphides nitrides)
ndash Engineered Conduction
ndash Brittle inelastic
Chapter 1 - 5
1 Pick Application Determine required Properties
Processing changes structure and overall shape
ex casting sintering vapor deposition doping
forming joining annealing
Properties mechanical electrical thermal optical
corrosive
Material structure composition
2 Properties Identify candidate Material(s)
3 Material Identify required Processing
The Materials Selection Process
Chapter 1 - 6
ELECTRICAL
bull Electrical Resistivity of Copper
bull Adding ldquoimpurityrdquo atoms to Cu (Cu-Ni alloy) increases resistivity
bull Deforming Cu increases resistivity
Adapted from Fig 188 Callister amp
Rethwisch 8e (Fig 188 adapted
from JO Linde Ann Physik 5 219
(1932) and CA Wert and RM
Thomson Physics of Solids 2nd
edition McGraw-Hill Company New
York 1970)
T (ordmC) -200 -100 0
1
2
3
4
5
6
Resis
tivity
r
(10
-8 O
hm
-m)
0
Chapter 1 - 7
THERMAL bull Space Shuttle Tiles -- Silica fiber insulation
offers low heat conduction
bull Thermal Conductivity
of Copper -- It decreases when
you add zinc
Adapted from
Fig 194W Callister
6e (Courtesy of
Lockheed Aerospace
Ceramics Systems
Sunnyvale CA)
(Note W denotes fig
is on CD-ROM)
Adapted from Fig 194 Callister amp Rethwisch
8e (Fig 194 is adapted from Metals Handbook
Properties and Selection Nonferrous alloys and
Pure Metals Vol 2 9th ed H Baker
(Managing Editor) American Society for Metals
1979 p 315)
Composition (wt Zinc) T
herm
al C
ond
uctivity
(Wm
-K)
400
300
200
100
0 0 10 20 30 40
100 mm
Adapted from chapter-
opening photograph
Chapter 17 Callister amp
Rethwisch 3e (Courtesy
of Lockheed
Missiles and Space
Company Inc)
Chapter 1 - 8
bull Transmittance -- Aluminum oxide may be transparent translucent or
opaque depending on the material structure
Adapted from Fig 12
Callister amp Rethwisch 8e
(Specimen preparation
PA Lessing photo by S
Tanner)
single crystal
polycrystal
low porosity
polycrystal
high porosity
OPTICAL
Chapter 1 - 9
bull Use the right material for the job
bull Understand the relation among properties
structure processing and performance
bull Recognize new design opportunities offered
by materials selection
Course Goals
SUMMARY
Chapter 1 - 10
ISSUES TO ADDRESS
bull What promotes bonding
bull What types of bonds are there
bull What properties are inferred from bonding
Chapter 2 Atomic Structure amp
Interatomic Bonding
Chapter 1 - 11
Atomic Structure
bull Atom ndash electrons ndash 911 x 10-31 kg protons neutrons
bull Atomic number = of protons in nucleus of atom = of electrons of neutral species
bull A [=] atomic mass unit = amu = 112 mass of 12C Atomic wt = wt of 6022 x 1023 molecules or atoms
1 amuatom = 1gmol
C 12011 H 1008 etc
167 x 10-27 kg
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 3
ex hardness vs structure of steel bull Properties depend on structure
Data obtained from Figs 1030(a)
and 1032 with 4 wt C composition
and from Fig 1114 and associated
discussion Callister amp Rethwisch 8e
Micrographs adapted from (a) Fig
1019 (b) Fig 930(c) Fig 1033
and (d) Fig 1021 Callister amp
Rethwisch 8e
ex structure vs cooling rate of steel bull Processing can change structure
Structure Processing amp Properties
Hard
ness (
BH
N)
Cooling Rate (ordmCs)
100
2 00
3 00
4 00
5 00
6 00
001 01 1 10 100 1000
(d)
30 mm (c)
4 mm
(b)
30 mm
(a)
30 mm
Chapter 1 - 4
Classes of Engineered Materials bull Metals
ndash High thermal amp electrical conductivity
ndash Opaque reflective strong ductile
bull Polymersplastics Covalent bonding sharing of ersquos
ndash Thermal amp electrical insulators
ndash Optically translucent or transparent
ndash Soft ductile low strength low density
bull Ceramics ionic bonding (refractory) ndash compounds of metallic
amp non-metallic elements (oxides carbides nitrides sulfides)
ndash Non-conducting (insulators)
ndash Brittle glassy inelastic
bull Semiconductors covalent Mixed (ionic) ndash elements (silicon
germanium) or compounds of metallic amp non-metallic elements (arsenides phosphides nitrides)
ndash Engineered Conduction
ndash Brittle inelastic
Chapter 1 - 5
1 Pick Application Determine required Properties
Processing changes structure and overall shape
ex casting sintering vapor deposition doping
forming joining annealing
Properties mechanical electrical thermal optical
corrosive
Material structure composition
2 Properties Identify candidate Material(s)
3 Material Identify required Processing
The Materials Selection Process
Chapter 1 - 6
ELECTRICAL
bull Electrical Resistivity of Copper
bull Adding ldquoimpurityrdquo atoms to Cu (Cu-Ni alloy) increases resistivity
bull Deforming Cu increases resistivity
Adapted from Fig 188 Callister amp
Rethwisch 8e (Fig 188 adapted
from JO Linde Ann Physik 5 219
(1932) and CA Wert and RM
Thomson Physics of Solids 2nd
edition McGraw-Hill Company New
York 1970)
T (ordmC) -200 -100 0
1
2
3
4
5
6
Resis
tivity
r
(10
-8 O
hm
-m)
0
Chapter 1 - 7
THERMAL bull Space Shuttle Tiles -- Silica fiber insulation
offers low heat conduction
bull Thermal Conductivity
of Copper -- It decreases when
you add zinc
Adapted from
Fig 194W Callister
6e (Courtesy of
Lockheed Aerospace
Ceramics Systems
Sunnyvale CA)
(Note W denotes fig
is on CD-ROM)
Adapted from Fig 194 Callister amp Rethwisch
8e (Fig 194 is adapted from Metals Handbook
Properties and Selection Nonferrous alloys and
Pure Metals Vol 2 9th ed H Baker
(Managing Editor) American Society for Metals
1979 p 315)
Composition (wt Zinc) T
herm
al C
ond
uctivity
(Wm
-K)
400
300
200
100
0 0 10 20 30 40
100 mm
Adapted from chapter-
opening photograph
Chapter 17 Callister amp
Rethwisch 3e (Courtesy
of Lockheed
Missiles and Space
Company Inc)
Chapter 1 - 8
bull Transmittance -- Aluminum oxide may be transparent translucent or
opaque depending on the material structure
Adapted from Fig 12
Callister amp Rethwisch 8e
(Specimen preparation
PA Lessing photo by S
Tanner)
single crystal
polycrystal
low porosity
polycrystal
high porosity
OPTICAL
Chapter 1 - 9
bull Use the right material for the job
bull Understand the relation among properties
structure processing and performance
bull Recognize new design opportunities offered
by materials selection
Course Goals
SUMMARY
Chapter 1 - 10
ISSUES TO ADDRESS
bull What promotes bonding
bull What types of bonds are there
bull What properties are inferred from bonding
Chapter 2 Atomic Structure amp
Interatomic Bonding
Chapter 1 - 11
Atomic Structure
bull Atom ndash electrons ndash 911 x 10-31 kg protons neutrons
bull Atomic number = of protons in nucleus of atom = of electrons of neutral species
bull A [=] atomic mass unit = amu = 112 mass of 12C Atomic wt = wt of 6022 x 1023 molecules or atoms
1 amuatom = 1gmol
C 12011 H 1008 etc
167 x 10-27 kg
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 4
Classes of Engineered Materials bull Metals
ndash High thermal amp electrical conductivity
ndash Opaque reflective strong ductile
bull Polymersplastics Covalent bonding sharing of ersquos
ndash Thermal amp electrical insulators
ndash Optically translucent or transparent
ndash Soft ductile low strength low density
bull Ceramics ionic bonding (refractory) ndash compounds of metallic
amp non-metallic elements (oxides carbides nitrides sulfides)
ndash Non-conducting (insulators)
ndash Brittle glassy inelastic
bull Semiconductors covalent Mixed (ionic) ndash elements (silicon
germanium) or compounds of metallic amp non-metallic elements (arsenides phosphides nitrides)
ndash Engineered Conduction
ndash Brittle inelastic
Chapter 1 - 5
1 Pick Application Determine required Properties
Processing changes structure and overall shape
ex casting sintering vapor deposition doping
forming joining annealing
Properties mechanical electrical thermal optical
corrosive
Material structure composition
2 Properties Identify candidate Material(s)
3 Material Identify required Processing
The Materials Selection Process
Chapter 1 - 6
ELECTRICAL
bull Electrical Resistivity of Copper
bull Adding ldquoimpurityrdquo atoms to Cu (Cu-Ni alloy) increases resistivity
bull Deforming Cu increases resistivity
Adapted from Fig 188 Callister amp
Rethwisch 8e (Fig 188 adapted
from JO Linde Ann Physik 5 219
(1932) and CA Wert and RM
Thomson Physics of Solids 2nd
edition McGraw-Hill Company New
York 1970)
T (ordmC) -200 -100 0
1
2
3
4
5
6
Resis
tivity
r
(10
-8 O
hm
-m)
0
Chapter 1 - 7
THERMAL bull Space Shuttle Tiles -- Silica fiber insulation
offers low heat conduction
bull Thermal Conductivity
of Copper -- It decreases when
you add zinc
Adapted from
Fig 194W Callister
6e (Courtesy of
Lockheed Aerospace
Ceramics Systems
Sunnyvale CA)
(Note W denotes fig
is on CD-ROM)
Adapted from Fig 194 Callister amp Rethwisch
8e (Fig 194 is adapted from Metals Handbook
Properties and Selection Nonferrous alloys and
Pure Metals Vol 2 9th ed H Baker
(Managing Editor) American Society for Metals
1979 p 315)
Composition (wt Zinc) T
herm
al C
ond
uctivity
(Wm
-K)
400
300
200
100
0 0 10 20 30 40
100 mm
Adapted from chapter-
opening photograph
Chapter 17 Callister amp
Rethwisch 3e (Courtesy
of Lockheed
Missiles and Space
Company Inc)
Chapter 1 - 8
bull Transmittance -- Aluminum oxide may be transparent translucent or
opaque depending on the material structure
Adapted from Fig 12
Callister amp Rethwisch 8e
(Specimen preparation
PA Lessing photo by S
Tanner)
single crystal
polycrystal
low porosity
polycrystal
high porosity
OPTICAL
Chapter 1 - 9
bull Use the right material for the job
bull Understand the relation among properties
structure processing and performance
bull Recognize new design opportunities offered
by materials selection
Course Goals
SUMMARY
Chapter 1 - 10
ISSUES TO ADDRESS
bull What promotes bonding
bull What types of bonds are there
bull What properties are inferred from bonding
Chapter 2 Atomic Structure amp
Interatomic Bonding
Chapter 1 - 11
Atomic Structure
bull Atom ndash electrons ndash 911 x 10-31 kg protons neutrons
bull Atomic number = of protons in nucleus of atom = of electrons of neutral species
bull A [=] atomic mass unit = amu = 112 mass of 12C Atomic wt = wt of 6022 x 1023 molecules or atoms
1 amuatom = 1gmol
C 12011 H 1008 etc
167 x 10-27 kg
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 5
1 Pick Application Determine required Properties
Processing changes structure and overall shape
ex casting sintering vapor deposition doping
forming joining annealing
Properties mechanical electrical thermal optical
corrosive
Material structure composition
2 Properties Identify candidate Material(s)
3 Material Identify required Processing
The Materials Selection Process
Chapter 1 - 6
ELECTRICAL
bull Electrical Resistivity of Copper
bull Adding ldquoimpurityrdquo atoms to Cu (Cu-Ni alloy) increases resistivity
bull Deforming Cu increases resistivity
Adapted from Fig 188 Callister amp
Rethwisch 8e (Fig 188 adapted
from JO Linde Ann Physik 5 219
(1932) and CA Wert and RM
Thomson Physics of Solids 2nd
edition McGraw-Hill Company New
York 1970)
T (ordmC) -200 -100 0
1
2
3
4
5
6
Resis
tivity
r
(10
-8 O
hm
-m)
0
Chapter 1 - 7
THERMAL bull Space Shuttle Tiles -- Silica fiber insulation
offers low heat conduction
bull Thermal Conductivity
of Copper -- It decreases when
you add zinc
Adapted from
Fig 194W Callister
6e (Courtesy of
Lockheed Aerospace
Ceramics Systems
Sunnyvale CA)
(Note W denotes fig
is on CD-ROM)
Adapted from Fig 194 Callister amp Rethwisch
8e (Fig 194 is adapted from Metals Handbook
Properties and Selection Nonferrous alloys and
Pure Metals Vol 2 9th ed H Baker
(Managing Editor) American Society for Metals
1979 p 315)
Composition (wt Zinc) T
herm
al C
ond
uctivity
(Wm
-K)
400
300
200
100
0 0 10 20 30 40
100 mm
Adapted from chapter-
opening photograph
Chapter 17 Callister amp
Rethwisch 3e (Courtesy
of Lockheed
Missiles and Space
Company Inc)
Chapter 1 - 8
bull Transmittance -- Aluminum oxide may be transparent translucent or
opaque depending on the material structure
Adapted from Fig 12
Callister amp Rethwisch 8e
(Specimen preparation
PA Lessing photo by S
Tanner)
single crystal
polycrystal
low porosity
polycrystal
high porosity
OPTICAL
Chapter 1 - 9
bull Use the right material for the job
bull Understand the relation among properties
structure processing and performance
bull Recognize new design opportunities offered
by materials selection
Course Goals
SUMMARY
Chapter 1 - 10
ISSUES TO ADDRESS
bull What promotes bonding
bull What types of bonds are there
bull What properties are inferred from bonding
Chapter 2 Atomic Structure amp
Interatomic Bonding
Chapter 1 - 11
Atomic Structure
bull Atom ndash electrons ndash 911 x 10-31 kg protons neutrons
bull Atomic number = of protons in nucleus of atom = of electrons of neutral species
bull A [=] atomic mass unit = amu = 112 mass of 12C Atomic wt = wt of 6022 x 1023 molecules or atoms
1 amuatom = 1gmol
C 12011 H 1008 etc
167 x 10-27 kg
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 6
ELECTRICAL
bull Electrical Resistivity of Copper
bull Adding ldquoimpurityrdquo atoms to Cu (Cu-Ni alloy) increases resistivity
bull Deforming Cu increases resistivity
Adapted from Fig 188 Callister amp
Rethwisch 8e (Fig 188 adapted
from JO Linde Ann Physik 5 219
(1932) and CA Wert and RM
Thomson Physics of Solids 2nd
edition McGraw-Hill Company New
York 1970)
T (ordmC) -200 -100 0
1
2
3
4
5
6
Resis
tivity
r
(10
-8 O
hm
-m)
0
Chapter 1 - 7
THERMAL bull Space Shuttle Tiles -- Silica fiber insulation
offers low heat conduction
bull Thermal Conductivity
of Copper -- It decreases when
you add zinc
Adapted from
Fig 194W Callister
6e (Courtesy of
Lockheed Aerospace
Ceramics Systems
Sunnyvale CA)
(Note W denotes fig
is on CD-ROM)
Adapted from Fig 194 Callister amp Rethwisch
8e (Fig 194 is adapted from Metals Handbook
Properties and Selection Nonferrous alloys and
Pure Metals Vol 2 9th ed H Baker
(Managing Editor) American Society for Metals
1979 p 315)
Composition (wt Zinc) T
herm
al C
ond
uctivity
(Wm
-K)
400
300
200
100
0 0 10 20 30 40
100 mm
Adapted from chapter-
opening photograph
Chapter 17 Callister amp
Rethwisch 3e (Courtesy
of Lockheed
Missiles and Space
Company Inc)
Chapter 1 - 8
bull Transmittance -- Aluminum oxide may be transparent translucent or
opaque depending on the material structure
Adapted from Fig 12
Callister amp Rethwisch 8e
(Specimen preparation
PA Lessing photo by S
Tanner)
single crystal
polycrystal
low porosity
polycrystal
high porosity
OPTICAL
Chapter 1 - 9
bull Use the right material for the job
bull Understand the relation among properties
structure processing and performance
bull Recognize new design opportunities offered
by materials selection
Course Goals
SUMMARY
Chapter 1 - 10
ISSUES TO ADDRESS
bull What promotes bonding
bull What types of bonds are there
bull What properties are inferred from bonding
Chapter 2 Atomic Structure amp
Interatomic Bonding
Chapter 1 - 11
Atomic Structure
bull Atom ndash electrons ndash 911 x 10-31 kg protons neutrons
bull Atomic number = of protons in nucleus of atom = of electrons of neutral species
bull A [=] atomic mass unit = amu = 112 mass of 12C Atomic wt = wt of 6022 x 1023 molecules or atoms
1 amuatom = 1gmol
C 12011 H 1008 etc
167 x 10-27 kg
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 7
THERMAL bull Space Shuttle Tiles -- Silica fiber insulation
offers low heat conduction
bull Thermal Conductivity
of Copper -- It decreases when
you add zinc
Adapted from
Fig 194W Callister
6e (Courtesy of
Lockheed Aerospace
Ceramics Systems
Sunnyvale CA)
(Note W denotes fig
is on CD-ROM)
Adapted from Fig 194 Callister amp Rethwisch
8e (Fig 194 is adapted from Metals Handbook
Properties and Selection Nonferrous alloys and
Pure Metals Vol 2 9th ed H Baker
(Managing Editor) American Society for Metals
1979 p 315)
Composition (wt Zinc) T
herm
al C
ond
uctivity
(Wm
-K)
400
300
200
100
0 0 10 20 30 40
100 mm
Adapted from chapter-
opening photograph
Chapter 17 Callister amp
Rethwisch 3e (Courtesy
of Lockheed
Missiles and Space
Company Inc)
Chapter 1 - 8
bull Transmittance -- Aluminum oxide may be transparent translucent or
opaque depending on the material structure
Adapted from Fig 12
Callister amp Rethwisch 8e
(Specimen preparation
PA Lessing photo by S
Tanner)
single crystal
polycrystal
low porosity
polycrystal
high porosity
OPTICAL
Chapter 1 - 9
bull Use the right material for the job
bull Understand the relation among properties
structure processing and performance
bull Recognize new design opportunities offered
by materials selection
Course Goals
SUMMARY
Chapter 1 - 10
ISSUES TO ADDRESS
bull What promotes bonding
bull What types of bonds are there
bull What properties are inferred from bonding
Chapter 2 Atomic Structure amp
Interatomic Bonding
Chapter 1 - 11
Atomic Structure
bull Atom ndash electrons ndash 911 x 10-31 kg protons neutrons
bull Atomic number = of protons in nucleus of atom = of electrons of neutral species
bull A [=] atomic mass unit = amu = 112 mass of 12C Atomic wt = wt of 6022 x 1023 molecules or atoms
1 amuatom = 1gmol
C 12011 H 1008 etc
167 x 10-27 kg
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 8
bull Transmittance -- Aluminum oxide may be transparent translucent or
opaque depending on the material structure
Adapted from Fig 12
Callister amp Rethwisch 8e
(Specimen preparation
PA Lessing photo by S
Tanner)
single crystal
polycrystal
low porosity
polycrystal
high porosity
OPTICAL
Chapter 1 - 9
bull Use the right material for the job
bull Understand the relation among properties
structure processing and performance
bull Recognize new design opportunities offered
by materials selection
Course Goals
SUMMARY
Chapter 1 - 10
ISSUES TO ADDRESS
bull What promotes bonding
bull What types of bonds are there
bull What properties are inferred from bonding
Chapter 2 Atomic Structure amp
Interatomic Bonding
Chapter 1 - 11
Atomic Structure
bull Atom ndash electrons ndash 911 x 10-31 kg protons neutrons
bull Atomic number = of protons in nucleus of atom = of electrons of neutral species
bull A [=] atomic mass unit = amu = 112 mass of 12C Atomic wt = wt of 6022 x 1023 molecules or atoms
1 amuatom = 1gmol
C 12011 H 1008 etc
167 x 10-27 kg
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 9
bull Use the right material for the job
bull Understand the relation among properties
structure processing and performance
bull Recognize new design opportunities offered
by materials selection
Course Goals
SUMMARY
Chapter 1 - 10
ISSUES TO ADDRESS
bull What promotes bonding
bull What types of bonds are there
bull What properties are inferred from bonding
Chapter 2 Atomic Structure amp
Interatomic Bonding
Chapter 1 - 11
Atomic Structure
bull Atom ndash electrons ndash 911 x 10-31 kg protons neutrons
bull Atomic number = of protons in nucleus of atom = of electrons of neutral species
bull A [=] atomic mass unit = amu = 112 mass of 12C Atomic wt = wt of 6022 x 1023 molecules or atoms
1 amuatom = 1gmol
C 12011 H 1008 etc
167 x 10-27 kg
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 10
ISSUES TO ADDRESS
bull What promotes bonding
bull What types of bonds are there
bull What properties are inferred from bonding
Chapter 2 Atomic Structure amp
Interatomic Bonding
Chapter 1 - 11
Atomic Structure
bull Atom ndash electrons ndash 911 x 10-31 kg protons neutrons
bull Atomic number = of protons in nucleus of atom = of electrons of neutral species
bull A [=] atomic mass unit = amu = 112 mass of 12C Atomic wt = wt of 6022 x 1023 molecules or atoms
1 amuatom = 1gmol
C 12011 H 1008 etc
167 x 10-27 kg
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 11
Atomic Structure
bull Atom ndash electrons ndash 911 x 10-31 kg protons neutrons
bull Atomic number = of protons in nucleus of atom = of electrons of neutral species
bull A [=] atomic mass unit = amu = 112 mass of 12C Atomic wt = wt of 6022 x 1023 molecules or atoms
1 amuatom = 1gmol
C 12011 H 1008 etc
167 x 10-27 kg
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 12
Atomic Structure
bull Valence electrons determine all of the
following properties
1) Chemical
2) Electrical
3) Thermal
4) Optical
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 13
Electronic Structure
bull
Quantum Designation
n = principal (energy level-shell) K L M N O (1 2 3 etc)
l = subsidiary (orbitals) s p d f (0 1 2 3hellip n -1)
ml = magnetic 1 3 5 7 (-l to +l)
ms = spin frac12 -frac12
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 14
Electron Energy States
1s
2s 2p
K-shell n = 1
L-shell n = 2
3s 3p M-shell n = 3
3d
4s
4p 4d
Energy
N-shell n = 4
bull Have discrete energy states
bull Tend to occupy lowest available energy state
eg Potassium (K) ndash 1s22s22p63s23p64s1
Electrons
Adapted from Fig 24
Callister amp Rethwisch 8e
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 15
bull Why Valence (outer) shell usually not filled completely
bull Most elements Electron configuration not stable
Survey of Elements
Electron configuration
(stable)
1s 2 2s 2 2p 6 3s 2 3p 6 (stable)
1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable)
Atomic
18
36
Element
1s 1 1 Hydrogen
1s 2 2 Helium
1s 2 2s 1 3 Lithium
1s 2 2s 2 4 Beryllium
1s 2 2s 2 2p 1 5 Boron
1s 2 2s 2 2p 2 6 Carbon
1s 2 2s 2 2p 6 (stable) 10 Neon 1s 2 2s 2 2p 6 3s 1 11 Sodium
1s 2 2s 2 2p 6 3s 2 12 Magnesium
1s 2 2s 2 2p 6 3s 2 3p 1 13 Aluminum
Argon
Krypton
Adapted from Table 22
Callister amp Rethwisch 8e
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 16
Electron Configurations
bull Valence electrons ndash those in unfilled shells
bull Filled shells more stable
bull Valence electrons are most available for bonding and tend to control the chemical properties
ndash example C (atomic number = 6)
1s2 2s2 2p2
valence electrons
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 17
The Periodic Table bull Columns Similar Valence Structure
Adapted from
Fig 26
Callister amp
Rethwisch 8e
Electropositive elements
Readily give up electrons
to become + ions
Electronegative elements
Readily acquire electrons
to become - ions
giv
e u
p 1
e-
giv
e u
p 2
e-
giv
e u
p 3
e- inert
gases
accept 1e
-
accept 2e
-
O
Se
Te
Po At
I
Br
He
Ne
Ar
Kr
Xe
Rn
F
Cl S
Li Be
H
Na Mg
Ba Cs
Ra Fr
Ca K Sc
Sr Rb Y
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 18
bull Ranges from 07 to 40
Smaller electronegativity Larger electronegativity
bull Large values tendency to acquire electrons
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Electronegativity
Also increases from bottom to top
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 19
Ionic Bond Metal + Non-metal
donates accepts
electrons electrons
Dissimilar electronegativities
ex MgO Mg 1s2 2s2 2p6 3s2 O 1s2 2s2 2p4
[Ne] 3s2
Mg2+ 1s2 2s2 2p6 O2- 1s2 2s2 2p6
[Ne] [Ne]
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 20
bull Occurs between + and - ions
bull Requires electron transfer
bull Large difference in electronegativity required
bull Example NaCl
Ionic Bonding
Na (metal) unstable
Cl (nonmetal) unstable
electron
+ - Coulombic Attraction
Na (cation) stable
Cl (anion) stable
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 21
Ionic Bonding
bull Attractive forces Depends on bonding
bull Repulsive forces Interactions between e- cloud
bull At FA + FR = 0 equilibrium
exists at atomic spacing r0
bull Potential energy E = int F dr
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 22
Ionic Bonding
bull Energy ndash minimum energy most stable
ndash Energy balance of attractive and repulsive
terms
Attractive energy EA
Net energy EN
Repulsive energy ER
Interatomic separation r
r A
n r B
EN = EA + ER = + -
Adapted from Fig 28(b)
Callister amp Rethwisch 8e
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 23
bull Predominant bonding in ceramics
Adapted from Fig 27 Callister amp Rethwisch 8e (Fig 27 is adapted from Linus Pauling The Nature of the
Chemical Bond 3rd edition Copyright 1939 and 1940 3rd edition Copyright 1960 by Cornell University
Examples Ionic Bonding
Give up electrons Acquire electrons
NaCl
MgO
CaF 2 CsCl
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 24
Examples Ionic Bonding (NaCl)
bull Coulombic attractive forces due
to +ve and ndashve charged ions
bull Ionic bonding is non-directional
bull Magnitude of the bond equal in
all directions
Adapted from Fig 29
Callister amp Rethwisch 8e
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 25
C has 4 valence e-
needs 4 more
H has 1 valence e-
needs 1 more
Electronegativities
are comparable
Adapted from Fig 210 Callister amp Rethwisch 8e
Covalent Bonding bull Similar electronegativity share electrons
bull Bonds determined by valence ndash s amp p orbitals
dominate bonding
bull Example CH4 shared electrons from carbon atom
shared electrons from hydrogen atoms
H
H
H
H
C
CH4
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 26
Mixed Bonding
bull Ionic-Covalent Mixed Bonding
ionic character =
where XA amp XB are the electronegativities and XA gt XB
bull Depends on relative positions of constituent atoms in periodic table
) 100 ( x
1-e-
(XA-XB )2
4
ionic 734 (100) x e1 characterionic 4
)2153(
2
-
--
Ex MgO XMg = 12 XO = 35
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 27
Metallic Bonding
bull Valence e- are not bound to any particular atom
bull Delocalized as electron cloud
bull Excellent conductors of heat and electricity
Adapted from Fig 211
Callister amp Rethwisch 8e
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 28
Arises from coulombic interaction between dipoles
bull Permanent dipoles-molecule induced
bull Fluctuating dipoles
-general case
-ex liquid HCl
-ex polymer
Adapted from Fig 213
Callister amp Rethwisch 8e
Adapted from Fig 215
Callister amp Rethwisch 8e
Secondary (van der Waals)
Bonding
asymmetric electron clouds
+ - + - secondary bonding
H H H H
H2 H2
secondary bonding
ex liquid H2
H Cl H Cl secondary
bonding
secondary bonding
+ - + -
secondary bonding
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 29
Type
Ionic
Covalent
Metallic
Secondary
Bond Energy
Large
Variable
large-Diamond
small-Bismuth
Variable
large-Tungsten
small-Mercury
Smallest
Comments
Nondirectional (ceramics)
Directional
(semiconductors ceramics
polymer chains)
Nondirectional (metals)
Directional
inter-chain (polymer)
inter-molecular
Summary Bonding
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 30
bull Bond Length r
bull Bond Energy Eo
bull Melting Temperature Tm
Tm is larger if Eo is larger
Properties From Bonding Tm
r o r
Energy
r
larger Tm
smaller Tm
Eo =
ldquobond energyrdquo
Energy
r o r
unstretched length
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 31
bull Modulus of elasticity (Youngrsquos modulus) E
bull Slope of stress-strain curve
depends on bond strength
E is larger if E0 is larger
Properties From Bonding E
= E F
A0
D L
L0
Hookes Law
s = E e
s
Linear- elastic
E
e
F
F simple tension test
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 32
Ceramics
(Ionic amp covalent bonding)
Large bond energy large Tm
large E
small a
Metals
(Metallic bonding)
Variable bond energy moderate Tm
moderate E
moderate a
Summary
Polymers (Covalent amp Secondary)
Directional Properties Secondary bonding dominates
small Tm
small E
large a
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 33
bullHow do atoms arrange themselves to form solids
bull Fundamental concepts and language
bull Unit cells
bull Crystal structures
1048766 Face-centered cubic
1048766 Body-centered cubic
1048766 Hexagonal close-packed
bull Close packed crystal structures
bull Density computations
bull Types of solids
Single crystal
Polycrystalline
Amorphous
How do atoms assemble into solid structures
Chapter 3 The Structure of Crystalline
Solids
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 34
Core Problems Ex 33
ANNOUNCEMENTS
Reading 31-37 317
38-315
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 35
SUMMARY
bull Atoms may assemble into crystalline or
amorphous structures
bull We can predict the density of a material provided we
know the atomic weight atomic radius and crystal
geometry (eg FCC BCC HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are
specified in terms of indexing schemes
Crystallographic directions and planes are related
to atomic linear densities and planar densities
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 36
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction is used for crystal structure and
interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 37
bull Non dense random packing
bull Dense ordered packing
Dense ordered packed structures tend to have
lower energies
Energy and Packing
Energy
r
typical neighbor bond length
typical neighbor bond energy
Energy
r
typical neighbor bond length
typical neighbor bond energy
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 38
bull atoms pack in periodic 3D arrays Crystalline materials
-metals
-many ceramics
-some polymers
bull atoms have no periodic packing
Noncrystalline materials
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2 Amorphous = Noncrystalline Adapted from Fig 323(b)
CampR8e
Adapted from Fig 323(a)
CampR8e
Materials and Packing
Si Oxygen
bull typical of
bull occurs for
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 39
bull Tend to be densely packed (billiard balls)
bull Reasons for dense packing
- Typically only one element is present so all atomic
radii are the same
- Metallic bonding is not directional
- Nearest neighbor distances tend to be small in
order to lower bond energy
- Electron cloud shields cores from each other
bull Have the simplest crystal structures
We will examine four such structures
Metallic Crystal Structures
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 40
bull Rare due to low packing density (only Po has this structure)
bull Close-packed directions are cube edges
bull Coordination = 6
( nearest neighbors)
Simple Cubic Structure (SC)
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 41
bull APF for a simple cubic structure = 052
APF =
a 3
4
3 p (05a) 3 1
atoms
unit cell atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF = Volume of atoms in unit cell
Volume of unit cell
assume hard spheres
Adapted from Fig 324 CampR8e
close-packed directions
a
R=05a
contains 8 x 18 = 1 atomunit cell
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 42
bull Coordination = 8
Adapted from Fig 32 CampR8e
bull Atoms touch each other along cube diagonals --Note All atoms are identical the center atom is shaded
differently only for ease of viewing
Body Centered Cubic Structure (BCC)
ex Cr W Fe (a) Tantalum Molybdenum
2 atomsunit cell 1 center + 8 corners x 18
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 43
Atomic Packing Factor BCC
a
APF =
4
3 p ( 3 a4 ) 3 2
atoms
unit cell atom
volume
a 3
unit cell
volume
length = 4R =
Close-packed directions
3 a
bull APF for a body-centered cubic structure = 068
a R Adapted from
Fig 32(a) CampR8e
a 2
a 3
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 44
bull Coordination = 12
Adapted from Fig 31 CampR8e
bull Atoms touch each other along face diagonals --Note All atoms are identical the face-centered atoms are shaded
differently only for ease of viewing
Face Centered Cubic Structure (FCC)
ex Al Cu Au Pb Ni Pt Ag
4 atomsunit cell 6 face x 12 + 8 corners x 18 Click once on image to start animation
(Courtesy PM Anderson)
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 45
bull APF for a face-centered cubic structure = 074
Atomic Packing Factor FCC
maximum achievable APF
APF =
4
3 p ( 2 a4 ) 3 4
atoms
unit cell atom
volume
a 3
unit cell
volume
Close-packed directions
length = 4R = 2 a
Unit cell contains 6 x 12 + 8 x 18 = 4 atomsunit cell
a
2 a
Adapted from
Fig 31(a)
CampR8e
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 46
A sites
B B
B
B B
B B
C sites
C C
C A
B
B sites
bull ABCABC Stacking Sequence
bull 2D Projection
bull FCC Unit Cell
FCC Stacking Sequence
B B
B
B B
B B
B sites C C
C A
C C
C A
A B
C
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 47
bull Coordination = 12
bull ABAB Stacking Sequence
bull APF = 074
bull 3D Projection bull 2D Projection
Adapted from Fig 33(a)
CampR8e
Hexagonal Close-Packed Structure
(HCP)
6 atomsunit cell
ex Cd Mg Ti Zn
bull ca = 1633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 48
Theoretical Density r
where n = number of atomsunit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadrorsquos number
= 6022 x 1023 atomsmol
Density = r =
VC NA
n A r =
Cell Unit of Volume Total
Cell Unit in Atoms of Mass
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 49
bull Ex Cr (BCC)
A = 5200 gmol
R = 0125 nm
n = 2 atomsunit cell
rtheoretical
a = 4R 3 = 02887 nm
ractual
a R
r = a3
5200 2
atoms
unit cell mol
g
unit cell
volume atoms
mol
6022 x 1023
Theoretical Density r
= 718 gcm3
= 719 gcm3
Adapted from
Fig 32(a) CampR8e
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 50
Densities of Material Classes
r metals gt r ceramics gt r polymers
Why
Data from Table B1 Callister amp Rethwisch 8e
r (g
cm
)
3
Graphite Ceramics Semicond
Metals Alloys
Composites fibers
Polymers
1
2
2 0
30 B ased on data in Table B1 Callister
GFRE CFRE amp AFRE are Glass Carbon amp Aramid Fiber-Reinforced Epoxy composites (values based on 60 volume fraction of aligned fibers
in an epoxy matrix) 10
3
4
5
03
04
05
Magnesium
Aluminum
Steels
Titanium
CuNi
Tin Zinc
Silver Mo
Tantalum Gold W Platinum
G raphite
Silicon
Glass - soda Concrete
Si nitride Diamond Al oxide
Zirconia
H DPE PS PP LDPE
PC
PTFE
PET PVC Silicone
Wood
AFRE
CFRE
GFRE
Glass fibers
Carbon fibers
A ramid fibers
Metals have bull close-packing
(metallic bonding)
bull often large atomic masses
Ceramics have bull less dense packing
bull often lighter elements
Polymers have bull low packing density
(often amorphous)
bull lighter elements (CHO)
Composites have bull intermediate values
In general
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 51
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 52
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 53
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 54
Fig 34 CampR8e
Crystal Systems
7 crystal systems
14 crystal lattices
Unit cell smallest repetitive volume which
contains the complete lattice pattern of a crystal
a b and c are the lattice constants
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 55
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 56
Point Coordinates
Point coordinates for unit cell center are
a2 b2 c2 frac12 frac12 frac12
Point coordinates for unit cell corner are 111
Translation integer multiple of lattice constants identical position in another unit cell
z
x
y a b
c
000
111
y
z
2c
b
b
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 57
Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of
unit cell dimensions a b and c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvw]
ex 1 0 frac12 =gt 2 0 1 =gt [ 201 ]
-1 1 1
families of directions ltuvwgt
z
x
Algorithm
where overbar represents a
negative index
[ 111 ] =gt
y
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 58
ex linear density of Al in [110]
direction
a = 0405 nm
Linear Density
bull Linear Density of Atoms LD =
a
[110]
Unit length of direction vector
Number of atoms
atoms
length
1 35 nm
a 2
2 LD -
Adapted from
Fig 31(a)
CampR8e
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 -
BCC vs simple cubic
59
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 -
BCC vs Simple C
bull Unit cell should reflect the symmetry of
the overall structure
bull If we look at smallest possible unit cell we
miss the symmetry of the structure
60
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 -
On to HCP
bull Same answer ndash sort ofhellip
bull What is the best unit cell for HCP structure
bull Smaller one is all we need but it doesnrsquot show
the symmetry When we speak of the hcp unit
cell we refer to the hexagonal one 61
c
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 -
Reading
bull 3-10 ndash 3-15
bull 4-1 ndash 4-7
bull 5-1 ndash 5-5
62
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 63
HCP Crystallographic Directions
1 Vector repositioned (if necessary) to pass
through origin
2 Read off projections in terms of unit
cell dimensions a1 a2 a3 or c
3 Adjust to smallest integer values
4 Enclose in square brackets no commas
[uvtw]
[ 1120 ] ex frac12 frac12 -1 0 =gt
Adapted from Fig 38(a)
CampR8e
dashed red lines indicate
projections onto a1 and a2 axes a1
a2
a3
-a3
2
a 2
2
a 1
- a3
a1
a2
z
Algorithm
In text example problems 38 and 39
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 64
HCP Crystallographic Directions bull Hexagonal Crystals
ndash 4 parameter Miller-Bravais lattice coordinates
are related to the direction indices (ie uvw)
as follows
w w
t
v
u
) v u ( + -
) u v 2 ( 3
1 -
) v u 2 ( 3
1 -
] uvtw [ ] w v u [
Fig 38(a) CampR8e
- a3
a1
a2
z
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 65
Crystallographic Planes
Adapted from Fig 310
CampR8e
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 66
Crystallographic Planes
bull Miller Indices Reciprocals of the (three) axial intercepts for a plane cleared of fractions amp common multiples All parallel planes have same Miller indices
bull Algorithm 1 Read off intercepts of plane with axes in terms of a b c 2 Take reciprocals of intercepts 3 Reduce to smallest integer values 4 Enclose in parentheses no commas ie (hkl)
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 67
Crystallographic Planes z
x
y a b
c
4 Miller Indices (110)
example a b c z
x
y a b
c
4 Miller Indices (100)
1 Intercepts 1 1
2 Reciprocals 11 11 1
1 1 0 3 Reduction 1 1 0
1 Intercepts 12
2 Reciprocals 1frac12 1 1
2 0 0 3 Reduction 2 0 0
example a b c
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 68
Crystallographic Planes
z
x
y a b
c
4 Miller Indices (634)
example 1 Intercepts 12 1 34
a b c
2 Reciprocals 1frac12 11 1frac34
2 1 43
3 Reduction 6 3 4
(001) (010)
Family of Planes hkl
(100) (010) (001) Ex 100 = (100)
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 69
Crystallographic Planes (HCP)
bull In hexagonal unit cells the same idea is
used
example a1 a2 a3 c
4 Miller-Bravais Indices (1011)
1 Intercepts 1 -1 1 2 Reciprocals 1 1
1 0
-1
-1
1
1
3 Reduction 1 0 -1 1
a2
a3
a1
z
Adapted from Fig 38(b)
CampR8e
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 70
Crystallographic Planes
bull We want to examine the atomic packing
of crystallographic planes
bull Iron foil can be used as a catalyst The
atomic packing of the exposed planes is
important
a) Draw (100) and (111) crystallographic planes
for Fe
b) Calculate the planar density for each of these
planes
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 71
Planar Density of (100) Iron
Solution At T lt 912ordmC iron has the BCC structure
(100)
Radius of iron R = 01241 nm
R 3
3 4 a
Adapted from Fig 32(c) CampR8e
2D repeat unit
= Planar Density = a 2
1
atoms
2D repeat unit
= nm2
atoms 121
m2
atoms = 12 x 1019
1
2
R 3
3 4 area
2D repeat unit
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 72
bull Some engineering applications require single crystals
bull Properties of crystalline materials
often related to crystal structure
(Courtesy PM Anderson)
-- Ex Quartz fractures more easily
along some crystal planes than
others
-- diamond single
crystals for abrasives
-- turbine blades
Fig 833(c) CampR8e (Fig
833(c) courtesy of Pratt
and Whitney) (Courtesy Martin Deakins
GE Superabrasives
Worthington OH Used with
permission)
Crystals as Building Blocks
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 73
Polycrystals
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 74
bull Single Crystals
-Properties vary with
direction anisotropic
-Example the modulus
of elasticity (E) in BCC iron
Data from Table 33
CampR8e (Source of data
is RW Hertzberg
Deformation and
Fracture Mechanics of
Engineering Materials
3rd ed John Wiley and
Sons 1989)
bull Polycrystals
-Properties maymay not
vary with direction
-If grains are randomly
oriented isotropic
(Epoly iron = 210 GPa)
-If grains are textured
anisotropic
200 mm Adapted from Fig
414(b) CampR8e
(Fig 414(b) is courtesy
of LC Smith and C
Brady the National
Bureau of Standards
Washington DC [now
the National Institute of
Standards and
Technology
Gaithersburg MD])
Single vs Polycrystals E (diagonal) = 273 GPa
E (edge) = 125 GPa
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 75
bull Most engineering materials are polycrystals
bull Each grain is a single crystal
bull If grains are randomly oriented
overall component properties are not directional
bull Grain sizes typically range from 1 nm to 2 cm
(ie from a few to millions of atomic layers)
A6 alloy ldquo the heat effected zonersquos (weld area) molecular structure is
reformed and A6 regains its original strengthrdquo
Nb-Hf-W plate with an
electron beam weld Adapted from Fig K color
inset pages of Callister 5e
(Fig K is courtesy of Paul E
Danielson Teledyne Wah
Chang Albany)
1 mm
Polycrystals
Isotropic
Anisotropic
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 76
Polymorphism
bull Two or more distinct crystal structures for the
same material (allotropypolymorphism)
titanium
a -Ti
carbon
diamond graphite
BCC
FCC
BCC
1538ordmC
1394ordmC
912ordmC
-Fe
-Fe
a-Fe
liquid
iron system
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 77
SUMMARY
bull Atoms may assemble into crystalline or amorphous structures
bull We can predict the density of a material provided we know the
atomic weight atomic radius and crystal geometry (eg FCC BCC
HCP)
bull Common metallic crystal structures are FCC BCC and
HCP Coordination number and atomic packing factor
are the same for both FCC and HCP crystal structures
bull Crystallographic points directions and planes are specified in
terms of indexing schemes
Crystallographic directions and planes are related to atomic linear
densities and planar densities
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations
Chapter 1 - 78
bull Some materials can have more than one crystal
structure This is referred to as polymorphism (or
allotropy)
SUMMARY
bull Materials can be single crystals or polycrystalline
Material properties generally vary with single crystal
orientation (ie they are anisotropic) but are generally
non-directional (ie they are isotropic) in polycrystals
with randomly oriented grains
bull X-ray diffraction (not discussed here) is used for crystal
structure and interplanar spacing determinations