The atomic structure of dislocations in h.c.p. metals II. Behaviour of the core under an applied stress

Abstract

The critical applied shear strain required to move the 1/3⟨1120⟩ dislocations studied in part I has been determined. In all cases, the form of the core changes substantially before dislocation motion eventually occurs. The basal-edge dislocation moves at the lowest strain, followed by the screw on the basal plane. Change in stacking-fault energy has little effect, and the stacking-fault ribbon almost disappears when motion occurs. The prism-edge dislocation moves without the dissociations postulated previously, and the effect of fault energy and c/a ratio are contrary to those anticipated. Cross-slip of the screw onto the prism plane requires the highest strain, but it occurs with an unexpected asymmetry, which is found to arise from the nature of Shockley partial dislocations.