Basal dislocation mobility in zinc single crystals

Abstract

Experimental measurements of basal dislocation mobility and the strain-rate sensitivity of the flow stress have been made on 99.999% pure zinc single crystals. Dislocation mobility in the [1210] (0001) basal slip system was measured by observing slip band growth produced by load pulses of controlled amplitude and duration. Local rearrangement of dislocations occurs at a resolved stress of 7 lb./in.^2. Slip bands are formed at stresses greater than 7 lb./in.^2, and their growth velocities are in the range of 7 to 80 cm/sec for shear stresses between 7 and 12 lb./in.^2. The results of the experimental measurements of dislocation mobility are discussed in relation to current theories. A comparison of the strain-rate sensitivity and the mobility measurements shows that a significant change in the density of moving dislocations is associated with a change in strain-rate. This change in density has generally been ignored by previous investigators. A dislocation model is proposed to explain the observed strain-rate sensitivity.