By means of Calphad (Calculation of PHAse Diagrams) approach, a thermodynamic optimization for the ternary system Mo-Nb-Ta was performed by considering experimental data available from the literature. Three binary systems Mo-Nb, Mo-Ta and Nb-Ta were evaluated first by using the experimentally measured emf data and phase diagram data. The parameters describing the Gibbs energies of all the assessed phases were given. The calculated thermodynamic property as well as phase diagrams agree well with the experimental ones. Several isothermal sections for the ternary system are calculated by extrapolation from the three boundary systems. The computed liquidus projection is compared with the experimental one. The general feature of the measured liquidus projection is reasonably described. The possible reason for small discrepancy is discussed.
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