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CRYSTAL DEFECTS

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.

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CRYSTAL DEFECTS

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  1. CRYSTAL DEFECTS Description & importance

  2. 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

  3. 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

  6. 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

  7. 2. Grain Boundaries

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

  9. QUESTIONS

  10. 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

  11. PHASE DIAGRAMS

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