Phase equilibria and thermodynamic assessment of the Mo–Nb-Re ternary system

Refractory elements are usually alloyed in the next-generation superalloys for better high-temperature stability and mechanical properties in the applications ranging from power plants to turbine blades in jet engines. Phase diagrams and thermodynamic models are the essential information for alloy design. Herein, the phase equilibria of the Mo–Nb-Re ternary system was investigated using the complementary methods including ab initio calculations at 0K, high-temperature experiments, and CALPHAD thermodynamic modeling. The ground-state formation enthalpy of the bcc, hcp, σ, and χ phases were determined. The as-cast Mo–Nb-Re alloy and those equilibrated at high temperatures (1973, 2173, and 2373K) were experimentally examined. With the ab initio energetics and high-temperature phase equilibria, the thermodynamic description (functions of Gibbs free energy) of the Mo–Nb-Re ternary system and subsystems was assessed or reassessed, which provides the foundation for further developments of superalloys.