DFT simulations of the self-healing behavior of a W〈110〉/W〈112〉 grain boundary in the presence of coexisting point defects

Light impurity atoms (LIAs), such as hydrogen and helium, tend to aggregate at pre-existing intrinsic point defects. This aggregation leads to detrimental effects, particularly in environments such as those foreseen in nuclear fusion reactors. There, such impurities would be ubiquitous, resulting in unacceptable material behavior that would unqualify the material as a Plasma Facing Material (PFM). One option to delay the degradation in performance is the use of nanostructured tungsten (NW), showing a large density of grain boundaries (GBs). Although we have already addressed the behavior of a single LIA in a GB, in this work we present the combined synergistic effects of the simultaneous presence of multiple LIAs, vacancies and Self-Interstitial Atoms (SIA) at semicoherent W/W interfaces using ab initio methods. Our results reveal a complex and interesting process in the competition between LIAs and SIAs. When the number of SIAs is low, He appears to hinder their recombination with vacancies, therefore casting doubts on the self-healing provided by NW. However, in the presence of larger numbers of SIAs, their mutual repulsion leads to the opposite behavior. Thus, a thorough thermodynamic assessment in which the evolution of the system may be tracked emerges as the crucial subsequent step in these investigations.