MAT E202 Lecture Notes - Lecture 5: Grain Boundary, Swaging, Extrusion

• School: University of Alberta
• Department: Materials Engineering
• Course: MAT E202
• Professor: Thomas Etsell

Document Summary

They interact, pile up and get entangled, making them progressively harder to move. From the s-s curve, you can see that more and more stress is needed to increase strain. Metals and alloys have many crystal defects called dislocations. When you cold work (plastically deform at room temperature), dislocations move and more are formed. In industry, there is cold work in many ways. As the ductility decreases, there is a limit to the amount of cold work that is allowable before cracks form. Fortunately, heating (annealing) the part allows diffusion of atoms from strained to unstrained regions, regrouping into strain-free crystals leading to softening and restoration of ductility. Heating up to 0. 3 - 0. 6 tm, which is the melting point in kelvin. Dislocations can now move to lower energy positions to relieve stress, producing subgrain boundaries in the original deformed grains. Atoms diffuse to form new stress-free equiaxed grains. As prior cold work increases, recrystallization temp goes down.