Cold worked, oxygen?free, electronic copper was heated to various temperatures for one hour and quenched to room temperature. Plot schematically the room temperature resistivity and hardness as a function of the annealing temperature, and explain the driving force and mechanisms for the changes in the resistivity and hardness.
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Solution:
Cold worked copper contains defects formed as a result of its deformation. These consist largely of vacancies and dislocations. Each of these vacancies and dislocations is associated with an inherent strain energy. Therefore, a plastically deformed material has a larger energy than an undeformed one, and is thermodynamically unstable. Given a combination of time and temperature; atoms in a deformed metal move so as to return the material to a lower state of energy, through the process of recovery, recrystallization, and grain growth. The resistivity and hardness changes, as functions of the annealing temperature assuming a constant time of annealing, will be similar to those shown in Fig. 8.4 for nickel. However, the recrystallization temperature will be around 400 K.
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