Modeling Solute-Dislocation Interactions in Body-Centered Cubic Alloys Using Kinetic Monte Carlo Simulations
- Author(s): ZHAO, YUE
- Advisor(s): Marian, Jaime
- Dezerald, Lucile
- et al.
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.