Vacancy accumulation mechanism at iron grain boundaries: The influence of grain boundary character and its coupling with grain size

Abstract

The interaction between the radiation defects of vacancies (Vs) and grain boundaries (GBs) is critical to the understanding of the radiation response of polycrystalline materials. In this work, by combing atomistic calculations with kinetic Monte Carlo methods, multiscale simulations of Vs behavior near different iron GBs were carried out to reveal the Vs accumulation mechanisms at GBs. On the one hand, the dependence of Vs accumulation on the GB character was clarified. At high temperature, new V escaping processes were revealed, including the emission from twin boundary and special coincidence site lattice (CSL) GB with a low V–GB binding strength and the leakage from the extremely low-angle GB with a bulk-like region between dislocation cores. These processes weaken the trapping efficiency of such GBs for Vs. Enhanced Vs trapping could be obtained for the general low-angle GB because of the large strain field. Due to the large V–GB binding energy and trapping site density, the general high-angle GB was found to capture Vs efficiently. On the other hand, the coupling of grain size with GB character via the combination of grain size, V formation energy at the GB and migration energy barrier within the GB was proposed, which leads to the competition between the V emission from the GB and its cruise along the GB. This accounts for the experimentally observed scattered relation of the radiation-performance to defect–GB binding strength. The present work provides some theoretical guidance for optimizing the radiation resistance of polycrystalline materials based on GB engineering.