Effect of order–disorder transition on thermodynamic and electronic properties of σ and χ phases in W–Re alloy: the first-principles calculation

The Tungsten–Rhenium (W–Re) alloys, celebrated for their high melting point, strength at elevated temperatures, electrical resistivity, and radiation resistance, have been widely utilized in high-temperature components, aerospace, electronics, and nuclear energy. As constituents of the topologically close-packed (TCP) phases, the sigma phase (σ) and chi phase (χ) formed within W–Re alloys wield considerable influence on the mechanical properties and the stability of the microstructure. First-principles calculations were utilized in the present work to explore the structural, thermodynamic, and electronic properties of both ordered and disordered configurations within the σ and χ phases, culminating in a systematic elucidation of the higher phase stability exhibited by the ordered structures. It is found that the bulk modulus of these two phases is directly proportional to the concentration of Re in the alloy, while the equilibrium volume is inversely proportional. The thermodynamic parameters of the σ and χ phases are calculated via the mean-field potential model. The similar trends observed in the isobaric heat capacity, enthalpy increment, and entropy change curves for these two phases suggest they possess comparable thermodynamic stability. It is noteworthy that the contribution of ionic vibrations predominantly affects the isobaric heat capacity, while the contribution of thermal electronic excitations increases linearly with temperature. Investigating the structure and thermodynamic properties of TCP phases in W–Re alloys at low temperatures has profound significance for optimizing material performance, microstructures features, establishing theoretical foundations, and predicting material behavior.