The Ta-B system: Key experiments and thermodynamic modeling

In the present work, the Ta-B system was thermodynamically optimized based on the CALPHAD method using data of liquidus temperatures, invariant transformations and enthalpy of formation from the literature as well as new experiments performed in our group. The phases Ta3B2, TaB(rt), Ta5B6, Ta3B4 were modeled as stoichiometric compounds. On the other hand, L (liquid), BCC, Ta2B, TaB(ht) and TaB2 were modeled as solution phases using the Compound Energy Formalism (CEF), with excess terms described by the Redlich-Kister polynomials. (βB) was treated as a pure element without any Ta solubility. The present thermodynamic modeling is in good agreement with the experimental data. •TaB2 homogeneity range at 1500 °C was studied by X-ray diffractometry.•High temperature modification (FeB-type) for the TaB phase and Ta5B6 stability were experimentally confirmed.•CALPHAD assessment of the Ta-B system is presented including new experimental results.•Solution phases were modeled according to their probable defect structures.