Harmonic effects in atomistic phase interactions between phonons and dislocations moving at relativistic velocities

Abstract

The observation of distinct velocity ‘plateaus’ below the upper limits of the sonic velocity have frustrated many in the scientific community studying high-velocity dislocation dynamics. Liebfried and Frank derived the well-established elastic models of dislocation motion, showing dislocation core energy approaches a relativistically infinite level at the limiting sonic velocity due to a singularity. Eshelby predicted the possibility of a single stable ‘transonic’ velocity with the Peierls-Nabarro model, however he could not provide a physical mechanism to explain the acceleration from the sub-sonic velocity limit. Weiner proposed a linear elastic model where the atomic masses within a dislocation move in a coordinated (or harmonic) manner due to coupled momentum transfer, and used this to predict the limiting velocity at 0 K. In modern times, detailed phonon dissipation models have been developed to predict the dislocation velocity relationships at higher temperatures. However, few studies have been performed to show how phonon interactions with dislocations influence the atomistic behaviour. This paper presents a conceptual model based on the coupled motion of multiple atoms in the dislocation core. When compared with molecular dynamics simulations, the model predicts key qualitative and quantitative metrics, such as the lower and upper limiting dislocation velocities. Detailed atomistic analysis confirms the in-phase coordination of atoms that become disrupted by interactions with dislocations at both limiting velocities. The model provides a physically realistic mechanism that is capable of explaining the observation of subsonic and transonic velocity plateaus.