Study of the Ni-rich multi-phase equilibria in Ni–Al–Pt alloys using the cluster/site approximation for the face-centered cubic phases

The modified cluster/site approximation was used to describe the thermodynamics of the various face-centered cubic phases in Ni–Al–Pt, the Bragg–Williams approximation for the B2 phase, and a modified regular solution formalism for the liquid phase. Coupled computational thermodynamics with key phase equilibrium measurements in the solid state, a thermodynamic description of this ternary for Ni contents higher than 50% was obtained based on these data and those given in the literature as well as the descriptions of its constituent binaries. Not only did the model-calculated solid-state phase equilibria agree with the measured data, the model-calculated liquidus projection is also able to account for the phases formed during solidification. In addition, the calculated chemical potentials or activities of Ni and Al are also in accord with the measured data as a function of temperature using mass spectrometry.