Basal dislocation interactions with a forest of non-basal dislocations in zinc

The mobility of basal dislocations in 99•999% pure zinc crystals with controlled densities of non-basal forest dislocations has been measured as a function of stress at temperatures of 298°K and 84°K. The range of the forest dislocation density was 10^2 to 10^6cm^(−2) and the range of the resolved shear stress was 0 to 34•2 × 10^6 dyne/cm^2. The mobility of dislocations was characterized by three distinct regions: a low-stress region showing no dislocation motion, a high-stress region with a linear velocity-stress relationship and, in between, a transition region, in accordance with theoretical predictions. The critical stress for basal edge dislocation motion was found to be proportional to the square root of the forest density and to be temperature-independent. A temperature-dependent critical stress for basal screw dislocations was observed. A strong interaction between basal dislocations and forest dislocations is indicated. In the high-stress region where dislocation velocity is a linear function of the stress the velocity is independent of the forest density. The values of drag coefficient B in this region are in good agreement with those previously reported for specimens with low forest densities (10^2 to 10^3 cm^(−2))