Dislocation motion in pure NaCl at low temperatures

Publisher Website
Google Scholar
Abstract
In annealed NaCl crystals of high purity, dislocation displacements under stress pulses at various temperatures obey Poisson type distributions which spread out toward larger distances with increasing time at constant stress. The calculated thermally-penetrable obstacle density of 105 cm−2 corresponds to that of the grown-in forest dislocations. The measurements suggest that the forest dislocations are flexible and are plucked by the glide dislocations at intersection, resulting in a displacement of the mechanical threshold stress to higher levels, and in an unusually small activation distance. The increase in the calculated activation distances with temperature suggests a split core. The stress dependence of the strain rate at yielding is compatible with the velocity-stress measurements for individual dislocations when account is taken of the stress dependence of the mobile dislocation density and of a temperature-dependent internal stress which results from multiplication of screw dislocations on secondary slip systems during pre-yield deformation. The measured rates of accumulation of glide and forest dislocations are of the required magnitudes to account for both the mobile dislocations and the internal stress.