Experimental investigation and thermodynamic modeling of the Ni-Ti-V system

The liquidus surface projection and isothermal section at 1273 K of the Ni-Ti-V system were established using X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersion spectroscopy (EDS), electron probe micro-analyzer (EPMA) and differential thermal analysis (DTA) techniques. Six primary solidification regions and four invariant reactions were deduced in the liquidus surface projection, and six three-phase regions were derived in the isothermal section at 1273 K. No ternary compound was observed. According to the experimental results in the present work and literatures, the Ni-Ti-V system was modeled by means of the CALPHAD (CALculation of PHAse Diagram) method. Two-sublattice model (NLTD)(10)(Ni,Ti)(20) for binary sigma phase was used, and the thermodynamic parameters of the sigma and NiV3 phases in the Ni-V system was reassessed. Solution phases (liquid, fcc, bcc and hcp) were modeled with the substitutional solution model in the Ni-Ti-V system. The compounds, Ni3Ti, NiTi2, Ni3V and sigma, were treated as (Ni,Ti,V)(m)(Ni,Ti,V)(n), and B2 were treated as (Ni,Ti,V)(0.5)(Ni,Ti,V)(0.5)Va(3.) A set of self-consistent thermodynamic parameters of individual phases was obtained.