Mapping strain rate dependence of dislocation-defect interactions by atomistic simulations

Significance Strain rate affects the dislocation interactions and plasticity in materials. Quantitative prediction of dislocation–defect interaction mechanisms and critical stresses as a function of strain rate, reaching down to the experimental deformation conditions much lower than 106 s–1, has been an outstanding challenge to traditional atomistic simulations. This study provides an original analytical and atomistic approach to predict dislocation-defect microstructure evolution at arbitrarily low strain rates. We demonstrated this model on a specific defect–dislocation system in zirconium, where the results bridge simulations to experiments, a paradigm that has been prohibitive to molecular dynamics. The principles in this study are broadly applicable to assessing the effects of strain rate on other defects with increasing complexities in a range of materials. Probing the mechanisms of defect–defect interactions at strain rates lower than 106 s−1 is an unresolved challenge to date to molecular dynamics (MD) techniques. Here we propose an original atomistic approach based on transition state theory and the concept of a strain-dependent effective activation barrier that is capable of simulating the kinetics of dislocation–defect interactions at virtually any strain rate, exemplified within 10−7 to 107 s−1. We apply this approach to the problem of an edge dislocation colliding with a cluster of self-interstitial atoms (SIAs) under shear deformation. Using an activation–relaxation algorithm [Kushima A, et al. (2009) J Chem Phys 130:224504], we uncover a unique strain-rate–dependent trigger mechanism that allows the SIA cluster to be absorbed during the process, leading to dislocation climb. Guided by this finding, we determine the activation barrier of the trigger mechanism as a function of shear strain, and use that in a coarse-graining rate equation formulation for constructing a mechanism map in the phase space of strain rate and temperature. Our predictions of a crossover from a defect recovery at the low strain-rate regime to defect absorption behavior in the high strain-rate regime are validated against our own independent, direct MD simulations at 105 to 107 s−1. Implications of the present approach for probing molecular-level mechanisms in strain-rate regimes previously considered inaccessible to atomistic simulations are discussed.

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