Effect of pressure on the interactions and phase diagrams of binary alloys

The phase diagrams of binary alloys have been found to vary with pressure. Within the framework of solution-type models, the variation is controlled by the pressure dependence of the elemental end members, which is relatively well known, and that of the excess interaction, which is relatively unknown. Exact thermodynamic relationships for the pressure and temperature dependence of the interaction parameters in an alloy solution are developed and related to the composition dependence of the excess thermodynamic quantities measured at ambient conditions. The effect of pressure modification of the interaction parameter on phase diagrams and solubility limits is explored in model systems identifying the critical role of the excess volume. It is found that the most significant pressure effects on the phase diagram are to be expected when the critical temperature associated with the solid solution interaction parameter is similar to the melting temperatures of the end-members and the excess volume of the is large.