Electronic-structure calculations of binary-alloy phase diagrams

A short-range-order--dependent electronic theory of coherent phase equilibrium in substitutional binary alloys is presented. The alloy internal energy is calculated using the cluster-Bethe-lattice method. The configurational entropy is evaluated using the cluster variation method. This approach is parameter free and uses only the results of elemental electronic-structure calculations as input. It is shown that the configuration dependence of the enthalpy of formation can be described by concentration-dependent effective pair interactions. Equilibrium phase diagrams for the Cr-W, Cr-Mo, and Mo-W systems are presented. Other thermodynamic properties can also be obtained. As an example, we calculate the chemical activities and high-temperature enthalpy of formation for the Cr-Mo system. The predicted phase diagrams and related thermodynamic functions are in good agreement with available experimental data.