CALPHAD-Based Thermodynamic Reassessment of Tb-Ni Binary System Supported by Ab-Initio Calculations

Abstract

First-principles calculations based on density functional theory (DFT) were employed to investigate the Tb-Ni binary system, and its thermodynamic characterization was reassessed utilizing the CALPHAD (CALculation of PHAse Diagram) methodology. The liquid solution is described by the Redlich-Kister polynomials model, while the binary compounds are treated as stoichiometric phases. The predicted formation enthalpies of all intermediate compounds in the Tb-Ni binary system were used to support the optimization. Leveraging the Thermo-Calc software, a self-consistent set of thermodynamic parameters was obtained. The calculated phase diagram aligns well with experimental phase equilibrium data from the literature, and the resulting thermodynamic properties exhibit greater reasonability. The trend in thermodynamic information across rare earth (RE)-Ni systems is highlighted, showing that with an increase in the RE atomic number, both the enthalpies of mixing of liquid alloys and the enthalpies of formation of intermetallic compounds become more negative.