Monte Carlo study of Cu precipitation in bcc-Fe: temperature-dependent cluster expansion versus local chemical environment potentials

Phase decomposition in binary Fe_1−xCu_x is studied using Monte Carlo simulations. Initially, density functional theory calculations are utilized to determine reference energies of various Fe–Cu compounds that serve as input for a temperature and composition-dependent cluster expansion. On this basis, the thermodynamic properties of the bcc Fe–Cu system are predicted and used to simulate the equilibrium constitution of bcc Cu-rich precipitates in an Fe-rich solid solution at various temperatures and supersaturations. Complementarily, computationally efficient pair potentials are developed in the local chemical environment approach that are calibrated on the first principles-cluster expansion results. These are then utilized in large-scale simulations for analysis of the multi-particle precipitate evolution. It is concluded that both approaches provide comparable information in terms of the precipitate radius as well as interface constitution. Whereas the cluster expansion ('full-information') path is especially useful in predicting energies of various ground state configurations for small systems, the local chemical environment approach ('fast-computation') path is particularly useful in evaluation of cluster formation kinetics and evolution statistics. (paper)