DYNAMIC INTERACTION OF IMPURITY ATMOSPHERES WITH MOVING DISLOCATIONS DURING STRESS-RELAXATION

The experimental results on stress relaxation show that in a certain r ange of temperatures and strain rates many dilute solid solutions, bot h interstitial and substitutional, exhibit a distinct transition from concave upward to concave downward log sigma-log epsilon curves. This behavior is related with the Portevin-Le Chatelier effect as was descr ibed by Van den Beukel. The stress relaxation curves are described by a physical model, presented in an earlier paper, which includes specif ic mechanism for dislocation motion, for the internal structure and fo r the interaction between impurities and dislocations. The model is te sted on a Cu-0.2 at% Zn alloy in the present work. Several microscopic parameters, such as the activation energy for the migration of the im purity, the binding energy between impurities and dislocations, the jo g concentration and the index m+beta in Van den Beukel's approach, are obtained from a fitting of the entire stress-relaxation curves to the model. The experimental evidence is in agreement with that from the o nset of serrated yielding.