Computer simulations study of iron–copper alloy

Abstract

The vessel steels of pressurised water reactors are embrittled by neutron irradiation. The changes of mechanical properties are commonly supposed to result from the formation of point defects, dislocation loops, voids and Cu-rich precipitates. The composition of such precipitates, specially the existence of vacancies, is not accessible through experiments. It is suggested that two mechanisms promote the formation of Cu-rich features in pressure vessel steels during neutron irradiation. When the Cu content is lower than 0.1%, solute-rich atmospheres can be formed in displacement cascades. For higher Cu contents, in addition to the latter phenomenon, a mechanism of accelerated precipitation can also induce the formation of Cu-rich clusters or precipitates. In order to understand all the mechanisms, Molecular Dynamics and Monte Carlo simulations have been carried out in pure Fe, and Fe–Cu alloys. Inter-atomic potentials of the Embedded Atom Method type, found in literature for pure Fe and pure Cu were used. We built a cross potential for the Fe–Cu interactions. It was fitted to thermodynamics and crystallographic properties of Fe–Cu alloys. The structure and properties of Cu–Vacancy(ies) clusters and Cu precipitates in bcc Fe have been studied by Monte Carlo simulations. Molecular Dynamics simulations of displacement cascades with different Primary Knocked-on Atom energies (1–20 keV) were carried out. Clusters containing Fe, Cu and vacancies were observed, located at the centre of the cascade. From our results, it appears that displacement cascades influence Cu clustering.