Internal friction due to the motion of geometric kinks on dislocations

Abstract

Internal-friction maxima due to dislocations, which are observed in metals at temperatures below the Bordoni relaxation, and manifest themselves only in the presence of pinners, e.g. impurities or radiation-induced point defects, have been conjectured to arise from an unidentified mode of unpinning at geometric kinks. At hertz and kilohertz frequencies they usually occur below 20K, so that the implied binding energies, a few millielectronvolts, are about two orders of magnitude too low to facilitate their assignment to conventional interactions between point defects and dislocations. A simple model, based on the migration of kink chains, is shown to account for the characteristic features of this damping. In this the pinners serve to constrain a significant fraction of the dislocations to lie across, rather than in, the Peierls valleys. The energy barriers are those controlling the stress-directed diffusion of geometric kinks trapped on such dislocations.