The kinetics of recovery and recrystallization of copper from hardness and thermoelectric-power measurements

Abstract

Annealing of H.C. copper strip cold-rolled with reductions in thickness of 50 per cent and 96 per cent has been studied as a rate-process by parallel observations of changes in hardness and thermoelectric power. In accordance with earlier investigations, change in hardness is taken to be proportional to fraction of metal recrystallized, while thermoelectric power is assumed to be directly related to residual elastic lattice strain. While the hardness—isothermal annealing curve of strip rolled 50 per cent exhibits a definite discontinuity indicative of two processes, such as recovery (or polygonization) and recrystallization, the thermoelectric power curve is, in agreement with Brindley's earlier conclusion, pseudo first order. The rate of decrease of average lattice strain during both polygonization and recrystallization is apparently governed by similar processes of dislocation migration. The annealing of heavily rolled strip is more complex; hardness and thermoelectric power curves, however, are identical, and analysis of the curves, outlined in an appendix, indicates that the dominant process is one of second order in agreement with previous findings. The second-order character follows naturally from the concept that decrease in thermoelectric power and softening occurs by direct interaction and annihilation of stress fields associated with stable arrays of dislocations at grain interfaces. It is pointed out that this concept is also consistent with recrystallization as a process of nucleation and growth.