Effect of temperature and shear direction on yield stress by {11 $$\bar 2$$ 2}〈 $$\overline {11} $$ 23〉 slip in HCP metals23〉 slip in HCP metals

Abstract

The yield shear stress τ y due to {11 $$\bar 2$$ 2}〈 $$\overline {11} $$ 23〉 second-order pyramidal slip system in cadmium, zinc, and magnesium hcp crystals increased with increasing temperature. This result is interpreted by two thermally activated processes as follows: (1) the dissociation of a (c+a) edge dislocation with a Burgers vector of 1/3〈 $$\overline {11} $$ 23〉 into a c sessile dislocation and an a glissile basal dislocation, and the subsequent immobilization of the (c+a) edge dislocation; (2) consequently, the double-cross slip of (c+a) screw dislocations must be activated thermally by an increment of applied stress to increase propagation velocity of slip band width. Moreover, τ y is affected strongly by a direction of applied shear force due to second-order pyramidal slip in zinc as well as in cadmium. The anomalous behaviors of yielding would be caused by the nonsymmetrical core structure of the (c + a) dislocation due to the lattice heterogeneity in hcp metals.