UCLA

Interactions among dislocations and solute atoms are the basis of several important processes in metal plasticity. In body-centered cubic (bcc) metals and alloys, low-temperature plastic flow is controlled by screw dislocation glide, which is known to take place by the

nucleation and sideward relaxation of kink pairs across two consecutive Peierls valleys. In alloys, dislocations and solutes affect each others kinetics via long-range stress field coupling and short-range inelastic interactions. It is known that in certain substitutional bcc alloys a transition from solute softening to solute hardening is observed at a critical concentration. In the first part of this work, we develop a kinetic Monte Carlo model of screw dislocation glide and solute diffusion in substitutional W–Re alloys. We find that dislocation kinetics is governed by two competing mechanisms. At low solute concentrations, nucleation is enhanced by the softening of the Peierls stress, which dominates over the elastic repulsion of Re atoms on kinks. This trend is reversed at higher concentrations, resulting in a minimum in the flow stress that is concentration and temperature dependent. This minimum marks the transition from solute softening to hardening, which is found to be in reasonable agreement with experiments.

In the second part of this work, we extend our model to interstitial W–O alloys. we report for the first time on simulations of jerky flow in W-O as a representative bcc interstitial solid solution. The simulations are carried out in a stochastic framework that naturally captures

rare events in a rigorous manner, enabling the study of solute diffusion and dislocation motion concurrently. The model has no adjustable parameters, with all coefficients calculated using first principles methods. We find that three regimes emerge from the stress-temperature space: one representative of standard solid solution strengthening, another mimicking solute cloud formation, and a third one, where the dynamic interaction of solutes and dislocations results in jerky flow and dynamic strain aging. We show how the symbiosis between quantum mechanical calculations and mesoscopic methods capable of furnishing diffusive timescales is a powerful demonstration of the capacities of physical models to explain macroscopic behavior.