MATS 3011 Lecture : Lecture 332014.pdf
Document Summary
Mechanism of plastic deformation: possibility 1: deformation occurs by planes sliding over each other. Atoms move from 1 position to anotherbut if look at table, much less bonds broken: possibility # 2: deformation via dislocation motion. Breaking of ~ 107 bonds/cmmuch less than possibility 1. Atoms themselves don"t move, but dislocation lines move --> requires less energy. For best practical crystal (ex: si, 104/m2) = For annealed (heated and then cooled down) metal = 10 10/m2. For cold-worked (strain/deform the material --> becomes strongerkind of like strain hardening) metal. If you have material w/ low vs high dislocation density: higher density --> more deformities/dislocations --> better plastic deformation. Matsci page 1 deformities/dislocations --> better plastic deformation. But if have way too many --> way too many dislocations --> will inhibit deformation motion --> even stronger. Dislocation = an extra half plane (edge type) or spiral type (screw type) Like dislocations repel, opposite dislocations attract and annihilate each other.
