Stress Relaxation in Single Crystals of Copper and α-Brasses

Abstract

Stress relaxation at constant strains has been studied in crystals of copper and α-brasses containing 10, 20, or 30 at.-% zinc at 77,200, and 291° K after consecutive small plastic deformations. Close to the yield point the relaxation was generally within 1% of the applied stress, but at large deformations, notably within the third stage of work-hardening, it attained ∼ 10%. Any given relaxation was observed for ∼ 1000 sec, over most of which period the decay of the stress was logarithmic in time. Energy barriers of the activated process were from ∼ 0.08 eV for copper and 0.2–0.3 eV for brasses. Their significance is discussed in terms of a model in which unpinning of dislocations from rows of solute atoms is the principal process determining the relaxation rate.