Low-temperature internal friction and thermal conductivity in plastically deformed metals due to dislocation dipoles and random stresses

TL;DR

This paper models how dislocation dipoles and random stresses affect low-temperature internal friction and thermal conductivity in plastically deformed metals, aligning theoretical predictions with experimental data.

Contribution

It introduces a modified string model accounting for dislocation dipoles and random forces, improving understanding of low-temperature mechanical and thermal properties of metals.

Findings

Dislocation dipoles explain thermal conductivity in superconducting samples.

Random forces on dislocation dipoles account for internal friction data.

Standard fluttering string mechanism is insufficient for internal friction modeling.

Abstract

The contribution to the low frequency internal friction and the thermal conductivity due to optically vibrating edge dislocation dipoles is calculated within the modified Granato-Lucke string model. The results are compared with the recent experiments on plastically deformed samples of Al, Ta and Nb at low temperatures. It is shown that the presence of a reasonable density of optically vibrating dislocation dipoles provides a good fit to the thermal conductivity in superconducting samples. At the same time, the internal friction experiments can not be described within the standard fluttering string mechanism. We found that the problem can be solved by assuming random forces acting on the dislocation dipoles. This gives an additional contribution to the internal friction which describes well the experimental data at low temperatures while their contribution to the thermal conductivity is found to be negligible.