Thermodynamic Analysis of the Phase Equilibria of the Nb–Ni–Ti System

Abstract

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 28 mol%Ni and 60 mol%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.