Third generation Calphad: Thermodynamic assessment of the Ni-Ga system with physics-based models

Abstract

Prediction of phase equilibria, phase stability, and thermodynamic properties is crucial in materials science. The second generation Calphad (CALculation of PHAse Diagrams) method faces challenges at low temperatures and in magnetic property predictions. To address these issues, the third generation Calphad is being developed, but its application has been limited primarily to unary systems, i.e., pure elements. Here we show the successful optimization of the Ni-Ga system, characterized by low melting point of Ga, magnetism of Ni, and ordered phases, using third generation thermodynamic models. We calculated the magnetic properties of fcc and bcc solution phases using Density Functional Theory (DFT) and fitted them with an improved magnetic model. Ordered phases were described using a four-sublattice model. The resulting parameters accurately reproduce experimental phase diagrams and thermochemical properties. This study demonstrates the successful application of the Equal Entropy Criteria (EEC) in a system where the constituent elements show quite different melting points. This work establishes a foundation for applying third generation Calphad to complex alloy systems, potentially enhancing the accuracy of material design and thus accelerating new materials development.