First-principles study of stability and local order in substitutional Ta-W alloys

A parameter-free electronic structure approach is applied to the study of stability and chemical order in substitutional bcc-based Ta-W alloys. The method is based on a Green's function description of the electronic structure of the random alloys. Configurational order is treated within the generalized perturbation method, and temperature effects are examined with a generalized mean-field approach. In contrast to the results summarized in the assessed phase diagram, an unambiguous tendency toward order with a $B2$ superstructure in a broad range of alloy composition is predicted. The details of the thermodynamics analysis, phase diagram, and short-range order are given for Ta-W alloys as a function of temperature and concentration.