ANOMALOUS TEMPERATURE-DEPENDENCE OF THE YIELD STRESS BY (11(2)OVER-BAR-2)((11)OVER-BAR-23) SECONDARY PYRAMIDAL SLIP IN CADMIUM CRYSTALS .2.MECHANISM

The yield stress due to {1122BAR}[1123BAR] second order pyramidal slip in cadmium crystal increases with increasing temperature. The mechani sm of this anomalous temperature dependence is proposed on the basis o f experimental results shown in our previous paper. A (c + a) edge dis location is dissociated into a c sessile dislocation and an a basal on e by thermally activated process, and the (c + a) edge dislocation is immobilized 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) sc rew dislocations must be activated thermally by a increment of applied stress to increase propagation velocity of slip band width. Since eac h of the mean free paths and the strain in slip bands is nearly consta nt independent of strain and strain rate, the increasing of propagatio n velocity with increasing strain rate is achieved also by an incremen t of applied stress.