CRYSTAL DEFECTSCRYSTAL DEFECTS
Description & importanceDescription & importance
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
TYPES OF DEFECTS
A. POINT DEFECTS OR ZERO-DIMENSIONAL DEFECTS
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1. VACANCY2. SELF-INTERSTITIAL
Important in diffusion
In pure metals In alloys
1. SUBSTITUTIONAL IMPURITY2. INTERSTITIAL IMPURITY
Important in strengthening
Mechanism of diffusion
VACANCY
B. Line defects or one-dimensional defects
Edge dislocation
Screw dislocation
VERY IMPORTANT IN PLASTIC DEFORMATION
C. Planar (surface) defects or two-dimensional defects1. Stacking Fault
Extrinsic stacking fault Intrinsic stacking faultPerfect stacking
B
A
A
B
AA
A
B
A
B
A
A
B
AA
A
B
A
B
A
A
B
AA
A
BA
CC
C
BC
C
BC
B
AB
AA
A
BCC
C
B
C
BCC
AA
2. Grain Boundaries
D. Volume defects or three-dimensional defects
Some scientists classify grains as volume defects
QUESTIONS
Some basics on alloys
Two types
Solid solutions CompoundsE.g. Fe3C, CuAl2
InterstitialSolid solutionE.g. Steel (Fe-C)Fe-0.2%C or Fe-0.4%C
SubstitutionalSolid solutionE.g. Brass (Cu-Zn)Cu-10%Zn or Cu-30%Zn
Cu Zn Fe C
PHASE DIAGRAMS