Thermodynamic reassessment of the Ni-Si-Ti system using a four-sublattice model for ordered/disordered fcc phases supported by first-principles calculations

A thermodynamic reassessment of the ternary Ni-Si-Ti system was performed by means of CALPHAD (CALculation of PHAse Diagram) method. The fcc_A1/Ni3Si-L12 disordered/ordered transition was described using a four-sublattice model. The enthalpies of formation of the ternary compounds τ1, τ2, and τ4 and end-members of the Ti5Si3 and Ni3Ti phases at 0 K in the Ni-Si-Ti ternary system were computed via first-principles calculations to supply necessary thermodynamic data for the CALPHAD modeling. In the Ni-Si-Ti ternary system, it was clarified that the ordered Ni3Si-L12 phase is formed from the liquid phase with the addition of Ti. An optimal set of thermodynamic parameters for the Ni-Si-Ti system was obtained by taking into consideration of the experimental data from the literature and theoretic values from the present first-principles calculations. Comparisons between the calculated and measured phase diagrams indicated that almost all the reliable experimental information was satisfactorily accounted for by the present modeling.