Dislocation mechanisms of low-temperature acoustic relaxation in iron

Abstract

An integrated approach to the study of the mechanisms of low-temperature dislocation relaxation during low-temperature cyclic deformations of crystalline materials has been developed and tested. The approach is based on the combined use of experimental methods of mechanical spectroscopy in wide frequency-temperature ranges and theoretical methods of statistical and thermoactivation analysis of experimental results. The efficiency of this approach was demonstrated by studying low-temperature relaxation resonances in iron crystals whose dislocation structure was varied by preliminary plastic deformation. In this study, the previous mechanical spectroscopy results for iron in the temperature range of 4 K < T < 150 K at vibrational frequencies of about 1 Hz and 105 Hz were supplemented by a detailed study of the temperature spectra of internal friction and the Young’s modulus of a single-crystal iron plate at intermediate frequencies of about 103 Hz. A two-mode dislocation relaxator model was suggested for interpreting the entire set of experimental results. Its first component is a linear segment of a dislocation line in a first-kind Peierls relief whose relaxation properties are determined by thermal activation of kink pairs. The second component is a chain of geometric kinks capable of thermally activated diffusion movement in a second-kind Peierls relief. Empirical estimates of the energy, force, inertial, and geometric characteristics of both components of such a relaxator have been obtained. This study complements the earlier analysis of the processes of mechanical relaxation in crystals caused by nucleation and movements of kinks on dislocation lines [a review: A. Seeger and C. Wüthrich, Nuovo Cimento B 33, 38 (1976)].