CRYSTAL DEFECTS

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CRYSTAL DEFECTS

• Description importance

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FUNDAMENTALS

• Metals are not perfect neither at the macrolevel
  and nor at the microlevel
• Contain a number of different types of
  crystalline defects (at the atomic level)
• Defects are important in many processes e.g.
  diffusion, deformation

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TYPES OF DEFECTS
A. POINT DEFECTS OR ZERO-DIMENSIONAL DEFECTS
In pure metals
In alloys
1. VACANCY 2. SELF-INTERSTITIAL
1. SUBSTITUTIONAL IMPURITY 2. INTERSTITIAL
IMPURITY
Important in strengthening
Important in diffusion
4
Mechanism of diffusion
VACANCY
5
B. Line defects or one-dimensional defects
Edge dislocation
Screw dislocation
VERY IMPORTANT IN PLASTIC DEFORMATION
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C. Planar (surface) defects or two-dimensional
defects
1. Stacking Fault
Extrinsic stacking fault
Intrinsic stacking fault
Perfect stacking
A
A
A
A
B
B
A
A
A
A
B
B
B
B
A
A
A
A
C
C
C
C
B
B
B
B
A
A
A
A
C
C
C
C
B
B
A
A
A
A
C
C
C
C
B
B
B
B
A
A
A
A
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2. Grain Boundaries
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D. Volume defects or three-dimensional defects
Some scientists classify grains as volume defects
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QUESTIONS
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Some basics on alloys

• Two types

Compounds E.g. Fe3C, CuAl2
Solid solutions
Interstitial Solid solution E.g. Steel
(Fe-C) Fe-0.2C or Fe-0.4C
Substitutional Solid solution E.g. Brass
(Cu-Zn) Cu-10Zn or Cu-30Zn
Cu
Zn
Fe
C
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PHASE DIAGRAMS