Phase diagram and thermochemical properties of the ZrTa system. An assessment based on Gibbs energy modelling

Abstract

The thermochemical properties of the ZrTa system are not known from direct measurements and there is a lack of information on the Gibbs energy ( G m ) of its various phases, which is necessary in systematic analyses of cohesive and thermal properties of transition metal systems, and in thermodynamic modelling of ternary and higher-order phase diagrams based on ZrTa. This kind of information has been obtained by using a theoretical method which relies on the coupling between thermochemistry and phase diagrams. The approach involves the analysis and synthesis of selected pieces of phase equilibrium data using models for G m of bcc, hcp and liquid, and the evaluation of a set of optimum model parameters through a computer optimisation technique. The G m functions arrived at in this way are applied to construct, by calculation, a phase diagram for the ZrTa system, which is used in critical comparisons with the experimental data available. In addition, the enthalpy of formation values generated by the present study are compared with estimates based on the Miedema method and other predictive approaches.