The formation of Cu-rich precipitates under irradiation was a major cause for changes in the mechanical response to load of reactor pressure vessel steels. In previous works, it was shown that the mechanism under which precipitation occurred was governed by diffusion of vacancy-copper (VCu) complexes, also in the absence of irradiation. Coarse-grained computer models (such as object kinetic Monte Carlo) aimed at simulating irradiation processes in model alloys or steels should therefore explicitly include the mobility of Cu precipitates, as a consequence of vacancy hops at their surface. To this end, diffusion coefficients and lifetimes were calculated for a large variety of VCu complexes. An innovative atomistic model was used in which  vacancy migration energies were calculated with little approximation, taking into account all effects of static relaxation and long-range chemical interaction as predicted by an interatomic potential. The results showed that, contrary to intuition, saturation in vacancies tended to slow the transport of Cu atoms.

Mobility and Stability of Large Vacancy and Vacancy-Copper Clusters in Iron: an Atomistic Kinetic Monte Carlo Study. N.Castin, M.I.Pascuet, L.Malerba: Journal of Nuclear Materials, 2012, 429[1-3], 315-24