An in situ study of prismatic glide in magnesium—II. Microscopic activation parameters

Abstract

The velocity of screw dislocations in nonbasal planes, is measured as a function of stress and temperature, in order to determine microscopic values of the activation parameters of the Friedel-Escaig mechanism (F.E. mechanism). In agreement with the model, the velocity of screw dislocations is proportional to their length (“length effect”). The microscopic activation area is 9 b 2 at 300 K, smaller than that deduced from macroscopic experiments, the latter being altered by a strong variation of the density of mobile dislocations with stress. The microscopic activation energy is 0.8 eV ± 0.1 eV between 300 and 373 K, in excellent agreement with that deduced from the F.E. model, thus confirming the validity of this model. The energy of two isolated kinks is estimated as more than 1.2 eV, which corresponds (using elastic calculations) to a stacking fault energy γ ≤ 50 ergs/cm 2, in the basal plane. The activation energy of creep between 400 and 600 K is then identified to that of the F.E. mechanism, thus confirming conclusions of the first part of this study.