Deformation by a kink mechanism in high temperature materials

A new double kink dislocation model has been developed to explain the tempe rature dependence of the yield stress in materials such as oxides and inter metallics that require high temperatures for plastic how. The major variati on in the free energy for the formation of a double kink nucleus with stres s is the kink-kink interaction energy. However, there is also a stress depe ndence of the pre-exponential factor in the strain rate constitutive equati on arising from kink diffusion. Numerical solution of the resulting equatio ns shows that there are temperature regimes where the stress varies logarit hmically with temperature. The model explains quantitatively the temperatur e dependence of the critical resolved shear stress on different slip system s for sapphire and spinel in terms of different activation energies for kin k diffusion. The model can be modified to explain compositional softening i n spinel by incorporating enhanced kink nucleation at cation vacancies. Thi s changes both the pre-exponential term and the activation energy and expla ins why the critical resolved shear stress (CRSS) decreases as the inverse of the square of the vacancy concentration, as is observed. (C) 1999 Publis hed by Elsevier Science Ltd on behalf of Acta Metallurgica Inc. All rights reserved.