Abstract
A microscopic theory of phase equilibrium in transition-metal alloys is presented. The approach is to combine a tight-binding cluster-Bethe-lattice method treatment of the internal energy with a cluster-variation method treatment of the configurational entropy. One of the great advantages of this approach is the inclusion of short-range order both in the internal energy and entropy calculation. The calculations are parameter free and use only the results of elemental electronic structure calculations as input, i.e., bandwidth and one-site energy. Calculations of the enthalpies of formation of Cr-Mo, Cr-W, Mo-W, Mo-Ta, Mo-Nb and Ta-W alloys are presented. The model is also used to calculate the miscibility gaps displayed by the Cr-Mo, Cr-W and Mo-W systems.