1977 Volume 18 Issue 7 Pages 527-534
An experimental study was carried out in order to investigate the contribution of basal and nonbasal dislocations (forest dislocations) to the early stage of the basal slip in 99.999% pure zinc single crystals compressed at room temperature. The relation between the basal shear stress and the shear strain was plotted and the increase in dislocation density during deformation was observed by means of the etch pit technique. The initial dislocation etch pit densities of the specimens used were 2.9×104∼3.7×104/cm2 on the (0001) surface and 6.1×104∼5.2×105/cm2 on the (11\bar20) surface. From these data, the length of basal and nonbasal dislocations per unit volume was calculated using equations developed by G. Schoeck. It was assumed that the density of forest dislocations did not change during the deformation since the critical resolved shear stresses for nonbasal slip systems were considerably higher than the stresses employed in the experiments. The results obtained were as follows. (1) The multiplication stresses were approximately equal to the stresses required to break up the attractive junctions between basal and forest dislocations. (2) The yield stresses were represented by the sum of the stress necessary for the forest cutting and the internal stress due to the basal dislocations. From these results, it was concluded that the yield stress was determined by the forest cutting under the internal stress field of the basal dislocations.
