Anomalous temperature dependence of the yield stress by {1122}〈1123〉 secondary pyramidal slip in cadmium crystals—I. Experiments

The yield stress due to {1122}〈1123〉second order pyramidal slip in cadmium crystal increases with increasing temperature. The mechanism of this anomalous temperature dependence is proposed on the basis of experimental results shown in our previous paper. A (c + a) edge dislocation is dissociated into a c sessile dislocation and an a basal one by thermally activated process, and the (c + a) edge dislocation is immobilzed as a result. The immobilization causes the mean free path of the edge dislocations and the strain in slip bands to decrease with increasing temperature. Consequently, double cross slip of (c + a) screw dislocations must be activated thermally by a increment of applied stress to increase propagation velocity of slip band width. Since each of the mean free paths and the strain slip bands is nearly constant independent of strain and strain rate, the increasing of propagating velocity with increasing strain rate is achieved also by an increment of applied stress.