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.