First-principles-based equilibrium Monte Carlo simulations of Cr-rich cluster stability in Fe–Cr–Al alloys: Effects of Al content and vacancies on the transition from promotion to suppression

Understanding the formation and stability of Cr-rich clusters (CrRCs) is essential for developing accident-tolerant oxide dispersion-strengthened Fe–Cr–Al alloys. This study employs first-principles-based equilibrium Monte Carlo simulations to quantitatively evaluate the effects of Al concentration and irradiation-induced vacancies on CrRC formation and atomic-scale structural behavior. Statistical metrics such as cluster size distribution, radial distribution functions, and short-range order parameters were used. With increasing Al content, CrRC formation exhibited a non-monotonic trend, peaking near 12 at.% Al. This aligns with prior static energy calculations but additionally captures Al segregation at CrRC–matrix interfaces and, at high Al concentrations, apparent Al incorporation within the cluster region causing structural diffusion and increased lattice displacement, which negatively impacts stability. Vacancies showed little direct effect on CrRC formation but strongly interacted with Al, co-segregating near interfaces. This Al–vacancy co-segregation may influence interface stability and diffusion under irradiation. These findings deepen atomic-scale understanding of CrRC behavior under thermal and irradiation conditions, providing foundational data for designing radiation-resistant Fe–Cr–Al alloys and supporting future mesoscale modeling.