DISLOCATION RELAXATION PROCESSES DUE TO KINK MIGRATION

The interpretation of the Bordoni relaxation and of related relaxation phenomena in terms of the thermally activated, stress-assisted format ion of kink pairs on dislocation lines is well established on assuming that the migration of kinks along dislocation lines is described by a high kink mobility mu(k). This assumption, however, is not valid if t he activation enthalpy for kink migration, H-m, is comparable with or even larger than the formation enthalpy of kink pairs or if even when small compared with the formation energy of kinks, H-m is larger than the lowest thermal energies accessible in internal friction experiment s. In those cases not only migration but also annihilation and trappin g of thermal kink pairs may produce internal friction peaks. The diffe rence-different equations governing the thermal kink pairs evolution a long dislocation lines under the action of a homogeneous applied shear stress are set up and their time-dependent solutions characterized by a set of relaxation times. It is shown how to obtain, from these solu tions, the internal friction spectrum under conditions that are experi mentally realized. Quantitative descriptions of geometrical kink migra tion and kink pair evolution are compared with selected experimental r esults.