Description & importance CRYSTAL DEFECTS Description & 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 In pure metals In alloys 1. VACANCY 2. SELF-INTERSTITIAL 1. SUBSTITUTIONAL IMPURITY 2. INTERSTITIAL IMPURITY Important in strengthening Important in diffusion

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 defects 1. Stacking Fault Perfect stacking Extrinsic stacking fault Intrinsic stacking fault 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

2. Grain Boundaries

D. Volume defects or three-dimensional defects Some scientists classify grains as volume defects

QUESTIONS

Some basics on alloys Two types Compounds E.g. Fe3C, CuAl2 Solid solutions Substitutional Solid solution E.g. Brass (Cu-Zn) Cu-10%Zn or Cu-30%Zn Interstitial Solid solution E.g. Steel (Fe-C) Fe-0.2%C or Fe-0.4%C Cu Zn Fe C

PHASE DIAGRAMS