Monte Carlo simulations were made of the first stages of the coherent precipitation of Cu in α-Fe. The method was based upon a vacancy-mediated diffusion model, which took account of the dependence of vacancy concentration and migration barrier upon the local atomic environment. These parameters were fitted to ab initio data, calculated within the density functional theory. The simulated precipitation kinetics were compared with experimental ones. The Fe-Cu system was characterized by a low mutual solubility, which resulted in the formation of almost pure Cu precipitates, and by a large difference between the vacancy formation energy in body-centred cubic Fe (~2.1eV) and metastable body-centred cubic Cu (~0.9eV), which led to a strong trapping of vacancies by the precipitates. As a result, precipitates which contained up to several tens of Cu atoms could be much more mobile than individual Cu atoms. This original result was analyzed by using a simple model of cluster diffusion. This suggested that the same behaviour could be observed in alloys having similar properties.

Cu-Precipitation Kinetics in α-Fe from Atomistic Simulations - Vacancy-Trapping Effects and Cu-Cluster Mobility. F.Soisson, C.C.Fu: Physical Review B, 2007, 76[21], 214102 (12pp)