Dislocation mechanisms of low temperature acoustic relaxation in the iron
A comprehensive 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. It is based on the combined use of experimental methods of mechanical spectroscopy and theoretical methods of statistical and thermoactivation analysis of experimental results. The efficiency of this approach is demonstrated by examining low-temperature relaxation resonances in iron crystals the dislocation structure of which was varied by preliminary plastic deformation. Previously obtained results of mechanical spectroscopy of iron in this study 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. The model of a two-mode dislocation relaxator is proposed to explain the entire set of experimental results. Its first component is a straight-line segment of a dislocation line in the Peierls relief of the first kind, whose relaxation properties are determined by the thermal activation of kink pairs. The second component is a chain of geometric kinks capable of thermally activated diffusion displacement in the Peierls relief of the second kind. Empirical estimates of the energy, force, inertial, and geometric characteristics of both components of such relaxator are obtained. This study complements the earlier analysis of the processes of mechanical relaxation in crystals, due to the initiation and displacement of kinks on dislocation lines (Review: A. Seeger and C. Wüthrich, Nuovo Cimento B 33, 38 (1976)).