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.