Atomistic predictions of dislocation nucleation with transition state theory

Abstract

The combined use of atomistic simulations and transition state theory (TST) has enabled significant improvements in the prediction of thermally activated processes in a wide range of applications, e.g., conformation changes in molecules, chemical reactions, kinetic phase transitions, and solid-state diffusion. However, such an approach is still in its infancy with regard to mechanics of materials applications. Focusing here on dislocation nucleation in Al, we examine the utility of five TST-based approaches. Using the finite-temperature string method, we interpret the success and failure of each approach in terms of a full energetic analysis of the nucleation processes. After showing that advanced TST approaches such as variational TST can accurately predict nucleation rates, we employ variational TST to study dislocation nucleation from a free surface under ordinary laboratory conditions. The predictions (1) demonstrate that nucleation will only occur under very high stresses at room temperature, (2) provide an upper bound on the shear strength of Al in dislocation starved contexts, and (3) provide a rate sensitivity signature of the nucleation process.