3.14 physical metallurgy 3.40j/22.71j modern physical ...li.mit.edu/stuff/pm/structures.pdf · 1...

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3.14 Physical Metallurgy 3.40J/22.71J Modern Physical Metallurgy

Structures – Properties – Processing – Functions theory

Acta Metallurgica (1953-1989)Acta Metallurgica et Materialia (1990-1995)

Acta Materialia (1996-present)

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Thermomechanical: “Heat and Beat”

Materials Processing

Chemical: alloy chemistry, doping,corrosion, oxidation

Radiation: exposure to light, electron beam, particles, neutrons

During processing, the material is often put in excited states, to achieve structural changes. These structural changes are preserved as the materials “cools down”, and taken advantage of (“properties”) during use. The whole process requires free-energy dissipation & varying degree of out-of-equilibriumness.

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Mechanical metallurgy: “Just beat, No heat”

progressivesurface.com/shotpeening.php

Creates compressive residual stress on the surface to delay fatigue crack initiation

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Electronic structure: it (x1,x2,…,xN) = H (x1,x2,…,xN)

Atomic structure: FCC, BCC, HCP, diamond cubic, liquid, glass, gas, …

Molecular structure: double stranded helical DNA, protein

Nanostructure: ZnO nanowire, Pt nanoparticle, …

Microstructure: grain boundaries, dislocation tangle, …

Mesostructure: pile of sand, …

Macrostructure: bicycle, Great Wall, …

Structure-property relationship

"One nanometer (one billionth of a meter) is a magicalpoint on the dimensional scale. Nanostructures are at the confluence of the smallest of human-made devices and the largest molecules of living systems..." - U.S. National Science Foundation, 2001, Nanoscale Sci. & Eng. Center program

"microstructure controls properties” - old-school metallurgists

World of Atoms & Electrons

Erwin SchrödingerNobel Prize in Physics

1933

Paul A.M. DiracNobel Prize in Physics

1933Materials | Chemistry | Life | Energy

6http://tu-freiberg.de/fakult4/imfd/cms/Multiscale/multiscale.html

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Dao et al, "Toward a quantitative understanding of mechanical behavior of nanocrystalline metals," Acta Mater. 55 (2007) 4041: Fig. 1. (a) Grain size dependence of strength of Cu. The strength (or hardness) is plotted vs. d-1/2. Literature data on hardness (solid symbols) and yield strength (multiplied by 3) from compression tests (empty symbols) are included in (a), and tensile yield strength are included in (b). The straight lines represent the H–P relation extrapolated from mc Cu. Note thatmost ultrafine crystalline Cu samples (with d in the submicron regime) exhibit higher hardness and tensile strength than the H–P expectation. The possible reason may be related with the fact that the ufc samples were prepared via severe plastic deformation, in which dense dislocation walls, tangles, cell walls or even subgrain boundaries are formed.

Metallographic Microscope

40× to 1600דmicrostructure”

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Microstructural Evolution versus Darwin’s Evolution?“A termite cathedral mound produced by a termite colony: a classic example of emergence in nature.” Fromhttp://en.wikipedia.org/wiki/Emergence

Arakawa et al, “Observation of the One-Dimensional Diffusion of Nanometer-Sized Dislocation Loops,” Science 318 (2007) 956.

bcc-Fe after 2000 keV e-beam radiation. Self-interstitial atoms agglomerated as loops,

vacancies agglomerated as voids.

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5800K

Carnot ideal heat engine efficiency:

(T1-T2)/T1

Cosmic radiationbackground: 2.7K

low-quality energy out

In terms of quantity: Ein ≈ EoutBut in terms of quality or free energy,

earth enjoys (spends) huge drop

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Free Energy ↔ Microstructure

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Residual Stress

Self-equilibrating body· = 0

does not mean (x = 0

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PalladiumIridium

austenite ferrite

graphite

ferromagneticCobalt ferromagnetic

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Coordination = 8

Coordination = 12

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[112]

[110]

[111]

FCC basal plane

Top plane

Middle plane

Bottom plane

Miller Index for Crystallographic Direction

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[hkl] ≡ ha1+ka2+la3<hkl> ≡ all symmetrypermutations of [hkl]

Miller Index for Crystallographic Plane

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(hkl) are planes parallel tothe plane that goes throughthree points h-1a1, k-1a2, l-1a3

{hkl} ≡ all symmetrypermutations of (hkl)

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Basal-a Prismatic-a

Pyramidal-a

2nd order Pyramidal-c+aPyramidal-c+a

Balasubramanian, Anand, "Plasticity of initially textured hexagonal polycrystals at high homologous temperatures: application to titanium," Acta Mater. 50 (2002) 133

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http://en.wikipedia.org/wiki/Stereographic_projection

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Polar angle “latitude”

Azimuthal angle “longitude”

ey

exm

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Polar angle “latitude”

Azimuthal angle “longitude”

ey

exm

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diad

triad

tetrad

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High index plane in zone of [111];Smaller dmin

Low index plane in zone of [111];Larger dmin

If ZA=[111]then all planeswith indiceson the equatorwill light up(approximately)

Relationship between stereographic projections and diffraction patterns

nstg.nevada.edu/tem/CHEM793_08/Lecture_14_1_CHEM793.pdf

110Ewald sphere center –k[110]

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http://en.wikipedia.org/wiki/File:Transformer3d_col3.svg

1388K1043KCurie temperature

627K

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BCC Fe-4wt% Si soft magnet: by a complex rolling / heat treatment procedure, it is possible to produce texture (B)

Rolling Direction(RD)

Transverse Direction (TD)

rolling plane Normal (ND)

http://en.wikipedia.org/wiki/File:Eulerangles.svg

Three Euler angles (,,)

“random” rotations:: [0,2]

cos: [0,2]

Adams, Wright, Kunze, "Orientation imaging - the emergence of a new microscopy," Metall Trans A 24 (1993) 819.

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Adams, Wright, Kunze, "Orientation imaging - the emergence of a new microscopy," Metall Trans A 24

(1993) 819.

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Adams, Wright, Kunze, "Orientation imaging - the emergence of a new microscopy," Metall Trans A 24

(1993) 819.

Rolling Direction

Transverse Direction

rolling plane normal

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“cube” texture

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equilibrium is however yet a bit more subtle:

It is possible to reach equilibrium among a subsetof the degrees of freedom

(all atoms in a shot) or subsystem, while this subsystem is not in equilibrium with

the rest of the system.

This is why engineering &material thermodynamics

are still useful in cars.

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Imagine a car going 80 mph on highway: the car is not in equilibrium with the road

the axel is not in equilibrium with the bodythe piston is not in equilibrium with the engine block …

But we may apply material thermodynamics to steel in piston, hydrogen in tank, rubber in tire… because there is a separation of timescales: atoms in condensed phases collide with each other ~ 1012 times per second, so atoms can reach equilibrium with adjacent

atoms before macro scale components reach equilibrium with each other.

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In this course, we will mainly study type A non-equilibrium phenomena, where temperature can be locally defined: T(x)

kBT1

atomic velocity

probability

kBT2

atomic velocity

representative volume element

(RVE)

52atomic velocity

3 2

3/ 2B B

| |exp(2 / ) 2

d mk T m k T

0v v v

far-from-equilibrium ions in Tokamak plasma:equilibrium Maxwellian distribution

v0

kBT

Probability

bimodal distribution:thus no concept of

temperature!

Equilibrium state → T, Stype B non-equilibrium state: no T, S