Decomposition kinetics of Fe-Cr solid solutions during thermal aging

The decomposition of Fe-Cr solid solutions during thermal aging is modeled by atomistic kinetic Monte Carlo simulations, using a rigid lattice approximation with pair interactions that depend on the local composition and temperature. The pair interactions are fitted on ab initio calculations of mixing energies and vacancy migration barriers at 0 K. The entropic contributions to the mixing of Fe-Cr alloys and to the vacancy formation and migration free energies are taken into account. The model reproduces the change in sign of the mixing energy with the alloy composition and gives realistic thermodynamic and kinetic properties, including an asymmetrical miscibility gap at low temperature and diffusion coefficients in good agreement with available experimental data. Simulations of short-range ordering and alpha-alpha' decomposition are performed at 773 and 813 K for Cr concentrations between 10% and 50%. They are compared with experimental kinetics based on three-dimensional atom probe and neutron scattering measurements. The possible effect of magnetic properties on diffusion in the alpha and alpha' phases, and therefore on the decomposition kinetics, is emphasized. DOI: 10.1103/PhysRevB.86.224109