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