Recovery and recrystallization of copper during stress relaxation after hot compression

Abstract

The kinetics of recovery and recrystallization of ETP copper undergoing stress relaxation was studied after high temperature compression and torsion. Two groups of specimens were strained to a common interruption stress: the first at 450°C, 1.8 × 10 −3s −1 and the second at 540°C, 9.3 × 10 −2s −1. A third group was tested in both compression and torsion at 450°C, 1.8 × 10 −1 s −1. After straining to 0.15, the samples were stress-relaxed or load-free annealed at the deformation temperature. The progress of restoration was followed by mechanical and metallographic methods. Recovery and recrystallization occurred under both relaxation and load-free annealing conditions. The former followed an exponential law and the latter the Mehl-Avrami relationship. The rates of recovery and recrystallization during relaxation were lower and higher, respectively, than during load-free annealing. Plastic flow in stress relaxation, by generating some degree of hardening, retards or offsets recovery, which in turn enhances recrystallization. The stress relaxation curve can be used to determine approximately the amount of softening and the onset and end of recrystallization.