First-principles design of high strength refractory high-entropy alloys

Valence electron concentration (VEC) is widely accepted as an effective guideline for designing the mechanical properties of Ti-containing refractory high-entropy alloys (RHEAs). In the present work, a series of Ti–Zr–Nb–Ta and Ti–Zr–Nb–Mo RHEAs with body-centered-cubic (bcc) structure are carefully designed by tailoring their VEC through changing the alloying composition. The elastic properties and mechanical properties are systematically calculated by using a first-principles method. Comparison with available experimental data demonstrates that the employed approach accurately describes the VEC dependence of the elastic and mechanical properties of RHEAs. In general, the elastic stability, elastic properties, ideal shear strength, Vickers hardness, and yield strength increase, whereas ductility and Zener anisotropy decrease with increasing VEC. Among all the considered RHEAs, the most isotropic RHEA Ti30Zr30Nb20Mo20 has the best strength-ductility trade-off. Mo has a stronger solid solution strengthening effect than Ta. The higher strength associates with larger lattice distortion induced by increasing VEC. Both elastic stability and mechanical properties are related to the electronic density of states of the alloys. The present work sheds deep insight into the design of high-performance RHEAs through tailoring the VEC.