Effect of alloying elements on the structure and mechanical properties of NbMoTaWX (X = Cr, V, Ti, Zr, and Hf) refractory high-entropy alloys

Numerous alloying elements can improve the mechanical properties of NbMoTaW refractory high-entropy alloys (RHEAs), but the relationship between the alloying of different elements and the changes in the microstructure and mechanical properties of RHEAs is ambiguous. The first principles based on density functional theory are used to calculate the lattice parameters, electronic properties, and elastic properties of NbMoTaW-based RHEAs to reveal the microstructure and mechanical properties of NbMoTaW RHEAs with alloying elements of the same period or subgroup. The melting point, lattice constant, and mass density of NbMoTaW-based RHEAs are controlled by the alloying elements such as Cr, V, Ti, Zr, and Hf. Valence electron concentration (VEC) is a key factor affecting the electronic structure and mechanical properties of NbMoTaW-based RHEAs. High VEC can improve the mechanical properties of RHEAs but reduce the ductility. Cr-alloying has a significant effect on mechanical properties of NbMoTaW RHEAs, and Ti has a significant effect on ductility. The orbital electronic interactions between the alloying elements and Nb, Mo, Ta, and W atoms shown by the density of states and electron density difference may explain the relationship between VEC and the mechanical properties of RHEAs. Our results provide the underlying insights needed to guide the design of NbMoTaW RHEAs with excellent mechanical properties.