Solution-based thermodynamic modeling of the Ni–Ta and Ni–Mo–Ta systems using first-principle calculations

Solution-based thermodynamic descriptions of the Ni–Ta and Ni–Mo–Ta systems are developed with supporting first-principles calculations and reported experimental data for parameter evaluation. For the Ni–Ta system, the liquid, bcc and fcc phases are described with a random solution model, D022–Ni3Ta is treated as a stoichiometric compound, and the remaining compounds are modeled as solid solutions on multiple sublattices. The resulting model for the Ni–Ta system is integrated with reported treatments of the Ni–Mo and Mo–Ta systems, and a thermodynamic model for the ternary Ni–Mo–Ta system is developed. The zero-Kelvin enthalpies of formation for the intermetallic compounds in the Ni–Mo–Ta system and the enthalpies of mixing for the bcc and fcc special quasirandom structures (SQS) in the binary Ni–Ta system are computed using the Vienna Ab-initio Simulation Package (VASP). Phase equilibria modeling results for the ternary Ni–Mo–Ta system are summarily presented in the form of isothermal sections and liquidus projections, with appropriate comparisons with available experimental data.