0
8.0kviews
Classify crystal imperfections

Mumbai University > Mechanical Engineering > Sem 4 > Material Technology

Marks: 5M

Year: May 2014

1 Answer
1
219views

Crystal Defects Classification:

  1. Point defects:
  2. Vacancy
  3. Schottky
  4. Self-Interstitial
  5. Frenkel
  6. Colour centers
  7. Polarons
  8. Excitons

  9. Line defects

  • Edge dislocation
  • Screw dislocation
  1. Surface defects
  • Grain boundaries
  • Tilt boundaries
  • Twin boundaries
  • Stacking faults
  1. Volume defects
  • Inclusions
  • Voids

enter image description here

Point defects

The simplest point defects are as follows:

  • Vacancy – missing atom at a certain crystal lattice position;
  • Interstitial impurity atom – extra impurity atom in an interstitial position;
  • Self-interstitial atom – extra atom in an interstitial position;
  • Substitution impurity atom – impurity atom, substituting an atom in crystal lattice.
  • Frankel defect – extra self-interstitial atom, responsible for the vacancy nearby.

Line defects

Linear crystal defects are edge and screw dislocations.

  • Edge dislocation is an extra half plane of atoms “inserted” into the crystal lattice. Due to the edge dislocations metals possess high plasticity characteristics: ductility and malleability.
  • Screw dislocation forms when one part of crystal lattice is shifted (through shear) relative to the other crystal part. It is called screw as atomic planes form a spiral surface around the dislocation line.

Planar defects

Planar defect is an imperfection in form of a plane between uniform parts of the material. The most important planar defect is agrain boundary. Formation of a boundary between two grains may be imagined as a result of rotation of crystal lattice of one of them about a specific axis. Depending on the rotation axis direction, two ideal types of a grain boundary are possible:

  • Tilt boundary – rotation axis is parallel to the boundary plane;
  • Twist boundary - rotation axis is perpendicular to the boundary plane
Please log in to add an answer.