Thermodynamic Modeling of B-Ta and B-C-Ta Systems

A thermodynamic assessment of the B-Ta system is performed using the CALPHAD method incorporating the latest experimental data and results from first-principles calculations of the formation enthalpies of TaB2, Ta3B4, TaB, Ta3B2, and Ta2B. The sublattice model of (Ta, B)(0.333)(Ta, B)(0.667) is used to describe the homogeneity range of TaB2, while the other four intermetallic compounds are treated as stoichiometric compounds. As a results, noticeable improvement were made over previous thermodynamic description of the B-Ta system. The thermodynamic parameters obtained in this study can effectively reproduce the most recently published experimental data. The thermodynamic assessment of the ternary phase diagram of B-C-Ta system could be carried out by combining the thermodynamic parameters of the C-Ta and B-C systems from the literature with the re-assessed B-Ta system. Reliable experimental data are satisfactorily accounted for the present thermodynamic description.