Thermodynamic description of the Ta–W–Zr system

The Ta–W, W–Zr and Ta–W–Zr systems are critically reviewed and modeled using the CALPHAD technique. The enthalpy of formation of the stoichiometric compound W2Zr in the W–Zr system is predicted from first-principles calculations. The solution phases (liquid, bcc and hcp) are modeled by the substitutional solution model. The compound W2Zr is treated with the formula (Ta,W)2Zr in the Ta–W–Zr system because of a significant solid solubility of Ta in W2Zr. All experimental data, including the Gibbs energy of formation, enthalpy of formation, activity of Ta and W of bcc phase at 1 200 K, Ta–W and W–Zr phase diagrams, and three isothermal sections of the Ta–W–Zr system at 1 073, 1 098, and 1 873 K, are reproduced in the present work. A set of self-consistent thermodynamic parameters of the Ta–W–Zr system is obtained.