ta 201 l3
TRANSCRIPT
THE NATURE AND PROPERTIES OF
MATERIALS
www.carsparefinder.co.uk Contd… from lecture 2
Edge DislocationEdge of an extra plane of atoms that
exists in the lattice
Symbol
Screw DislocationSpiral within the lattice structure wrapped
around an imperfection line, like a screw is wrapped around its axis
Screw Dislocation
Planar Defects
Imperfections that extend in two directions to form a boundary are called Planar Defects
• Examples:– Twining (Ti, Zn, Mg)– grain boundaries are internal surface
interruptions
Twinning
Twinning can be defined as a mechanism of deformation in which atoms in one side of a plane are shifted to form amirror image of the other side of the plane.
Twinning: microstructure
Non-crystalline Materials
Absence of long-range order in the molecular structure in a non-crystalline materials
Crystalline Non-Crystalline (Amorphous)
Non-crystalline Materials: Examples
Metallic glass
Crystalliene vs. Non-crystalline Materials: difference in behaviour
Supercooledliquid
m
Tg : Glass transitiontemperature
Tm : Melting temperature
ENGINEERING MATERIALS
Materials
Metal Non-metal
Ferrous
Non-Ferrous
CeramicsComposites
Plastics
ENGINEERING MATERIALS
Ferrous Materials
Steels
Fe-C alloy with C content varying from 0.02 – 2 wt%
Classification• Plain C steels• Alloy steels
Fe-C phase diagram: basis for steels and cast irons
Wt % C
•
•
20 40 60 80 10001000
1100
1200
1300
1400
1500
1600T(°C)
L (liquid)
α (FCC solid solution)
L + αliquidus
solidus
Wt% Ni
Phase Diagram
Solid Solution
Tetrahedral Void
Octahedral Void
Plain C Steels
Classification• Low C steel: < 0.3% C• Medium C Steel: 0.3 – 0.8% C• High C Steel: > 0.8% C
Small amounts of other elements (0.4% Mn, 0.05% S, 0.04% P)
↑ C content ↑ hardness and ↓ ductility
Alloy Steels
Definition• Alloy of iron and carbon containing high
amount of alloying element other than elements in carbon steels.
Properties• Gives better strength , ductility and
toughness compared to plain carbon steels.
Types of alloy steels• Stainless steel
– Large family of steel containing at least 11.5% Cr . Corrosion resistance due to formationof Cr2O3
• Tool steels– Contains elements such as C (0.8-1.3 %), Mn
(0.2-1.6 %) , Cr , W , Va , Mo , Co .– A class of high C alloy steels that is both
shock and wear resistant. – Withstand high temperatures.
Cast IronManufacture• Product that comes out of the BF is Pig
Iron– Composition: 3-4 % C, 1.5-2.5 % Mn , 1-3 %
Si + S and P• When it is cast directly it is called Cast Iron
• Good corrosion resistance– Corrodes readily under atmospheric conditions, then
protective film will form– Used in water pipes.
• Good vibration damping capacity– More than 100 times better than steel and 2000 times
better than Al– Fatigue resistant
• Machinability: Good to bad
UsageEngine blocksMachine frames