University:
York University
Course:
CHEM 1100 | Chemistry and Materials Science for Engineers
Academic year:

2021
Views:

240

Pages:

2
Author:

Nick T.

Linear defects: 1-dimensional effect around which atoms are misaligned. Edge dislocation: b is perpendicular Screw dislocation: b is parallel Burger's vector (b): measure of lattice distortion (magnitude + direction) Edge Dislocation: Localized lattice distortion Extra plane of atoms Caused during processing of material or heat treatment There is slight curvature due to stress introduced upon the lattice. Closer you are to the distortion, the more tense it is (localized = if close) Pull apart to make more space Squeeze to squeeze it into shape to minimize upper pull apart and distortion. Screw Dislocation: Formed by shear stress Example: Rubik's cube View from above: All atoms shift a bit in position. Upper part of lattice is shifted by unit cell difference. b goes with dislocation parallel to it (follows line of dislocation) In real life, defects coexist together in the same material. Mixed for regions in between A-B. Point defect: If there is a missing atom, for example, it will act as a trap of electrons and cause complications in the process of testing (distortion). Edge dislocation: extra half plane of atoms. Screw dislocation: Those dislocations can be visible through TEM (transmission electron microscopy). This is in low magnification. Two ways to check: Lines are clear, yes, but atoms cannot be seen. Grains are clear. By looking at this: Dark lines are dislocations. Fig. 4.6: Callister & Rethwisch, Be 0.2 μm In μm, not nano scale. Dislocations play a significant role in predicting plastic deformation of metals and ceramics.