Extracting free energy of clusters in concentrated binary alloys from atomistic Monte Carlo simulations

A good knowledge of clusters (thermal fluctuations or precipitates) free energy as a function of their size and temperature is essential to accurately describe nucleation and growth, even in binary alloys. Thanks to a Monte Carlo (MC) method, this quantity can be accurately calculated, but results are directly applicable only to dilute alloys. For concentrated alloys, results must be reinterpreted to account for the probability of coagulation between close clusters. To investigate this kind of situation with atomistic MC (AMC) simulations, ordered and coherent Al3Li clusters embedded in concentrated Al-Li alloys are considered. A classical pair potential limited to first and second nearest neighbours is proposed for this purpose. To enhance the MC calculation of cluster free energy, a new acceptance criterion related to the probability of coagulation is added to the classical energy one. It is shown that the properties of clusters can be directly extracted from AMC simulations. A few simple tests are provided to prove the consistency of this approach.