CBE30361 Lecture 15: Materials lecture 15
21 Mar 2016
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Tr = temperature at which recrystallization just reaches completion in 1 hour. Purity of metal -- tr decreases with increasing purity. Direct cold working does not work (it makes the material too brittle) The annealing process reverts all of the changes in the mechanical properties back to its original state, but keeps the change in diameter. Doesn"t change the mechanical properties: just changes the dimension. This is because it is being worked above the annealing temperature. So, for the previous example, could just hot work the material to get the intermediate cross- sectional area and then cold work it. Dislocations are observed primarily in metals and alloys. Strength is increased by making dislocation motion difficult. A cold-worked metal that is heat treated may experience recovery, recrystallization, and grain growth -- its properties will be altered. Usually is preventable: signs of failure can be seen. Can happen in very little time with very little warning.
