Application ofab initioand CALPHAD thermodynamics to Mo-Ta-W alloys

A parameter-free electronic structure approach is applied to the study of stability and chemical order in substitutional bcc-based Mo-Ta, Ta-W, and Mo-W alloys. The method is based on a Green's function description of the electronic structure of random alloys. Configurational order is treated within the generalized perturbation method, and temperature effects are accounted for by a generalized mean-field approach. The practical application of this study to phase stability in Mo-Ta-W alloys is tested by converting the ab initio output thermodynamics of the three binary subsystems to a format amenable to a CALPHAD treatment. The results of this conversion are then used to predict isothermal sections of the ternary phase diagram of the Mo-Ta-W system that are compared with the results obtained directly from the ab initio approach with the cluster variation method. It is concluded that the proposed CALPHAD conversion of the ab initio results is a viable scheme to capture the alloy properties predicted from first-principles electronic structure calculations.