Thermodynamic modeling of the Ni–Ti–Hf system

Ni–Ti–Hf alloys have received extensive attention owing to their excellent shape-memory behavior. In the present work, the thermodynamic assessment of the Ni–Ti–Hf system was performed using the CALPHAD method after a critical review of the thermodynamic descriptions of boundary binaries and available experimental data in the ternary system. The solubility ranges of the third elements in binary intermetallic compounds are well described. Moreover, the wide homogeneity ranges of the B2 and NiTi2 phases are satisfactorily reproduced. The ternary τ phase was reasonably described using a two-sublattice model (Ni)0.44(Hf,Ti)0.56. Both the thermochemical properties and phase diagrams were well described using the present model parameters.