Abstract
Determining the defect evolution beyond the molecular dynamics (MD) time scale is critical in bridging the gap between atomistic simulations and experiments. The recently developed self-evolving atomistic kinetic Monte Carlo (SEAKMC) method provides new opportunities to simulate long-term defect evolution with MD-like fidelity. In this study, SEAKMC is applied to investigate the cascade defect evolution in bcc iron. First, the evolution of a vacancy rich region is simulated and compared with results obtained using autonomous basin climbing (ABC) +KMC and kinetic activation-relaxation technique (kART) simulations. Previously, it is found the results from kART are orders of magnitude faster than ABC+KMC. The results obtained from SEAKMC are similar to kART but the time predicted is about one order of magnitude faster than kART. The fidelity of SEAKMC is confirmed by statistically relevant MD simulations at multiple higher temperatures, which proves that the saddle point sampling is close to complete in SEAKMC. The second is the irradiation-induced formation of C15 Laves phase nano-size defect clusters. In contrast to previous studies, which claim the defects can grow by capturing self-interstitials, we found these highly stable clusters can transform to <111> glissile configuration on a much longer time scale. Finally, cascade-annealing simulations using SEAKMC is compared with traditional object KMC (OKMC) method. SEAKMC predicts substantially fewer surviving defects compared with OKMC. The possible origin of this difference is discussed and a possible way to improve the accuracy of OKMC based on SEAKMC results is outlined. These studies demonstrate the atomistic fidelity of SEAKMC in comparison with other on-the-fly KMC methods and provide new information on long-term defect evolution in iron.
