Thermodynamic analysis of the phase equilibria of the Nb-Ni-Ti system

A thermodynamic analysis of the Nb - Ni - Ti system has been performed following the CALPHAD technique. To enable the thermodynamic description of the binary systems, the results from a previous evaluation were adopted for the Nb - Ni, Nb - Ti. and Ni - Ti systems. However, a slight modification of the parameters was applied to the bcc and Nb₆Ni₇ phases in the Nb - Ni system, when considering the ternary phase equilibria. The phase boundaries of the Nb - Ni - Ti ternary system at a constant 28mol%Ni and 60mol%Ni were determined experimentally by differential scanning calorimetry. A thermodynamic assessment of the ternary system was performed based on the experimental information as well as the reported phase boundaries of the isothermal sections of the Nb - Ni - Ti system at 700, 800, and 900°C. Our calculations reveal that this system includes 15 types of ternary invariant reactions. The ternary eutectic temperature was between 901.6 and 1063.7°C.