Composition-dependent synergistic effects of elements on elastic properties in the MoNbTaVW-series refractory...

MoNbTaW-based refractory high-entropy alloys exhibit excellent high-temperature mechanical properties, but their poor room-temperature ductility severely restricts engineering applications. Compositional optimization is an effective strategy for enhancing the mechanical properties of these alloys. However, the composition-dependent synergistic effects of group VB/VIB elements on elastic properties, along with the coupled regulatory mechanisms between the valence electron concentration (VEC) and the degree of atomic size mismatch (δ), remain unclear. These unresolved issues represent critical bottlenecks that hinder the compositional design of MoNbTaVW RHEAs with balanced strength and toughness.

First-principle calculations based on density functional theory (DFT) were performed with the CASTEP code to investigate the MoNbTaVW RHEA system. A BCC solid-solution model was established via a virtual crystal approximation (VCA) and fully relaxed via the BFGS algorithm. The PBE generalized gradient approximation and norm-conserving pseudopotentials are employed for total energy and elastic constant calculations. Lattice constants, elastic constants, VEC, and δ are computed for 21 alloy compositions spanning variations in Mo, Nb, Ta, V, and W. Polycrystalline bulk, shear, and Young's moduli are derived via the Voigt-Reuss-Hill averaging scheme, and mechanical stability is verified against the Born criteria for cubic crystals. The calculated properties are further correlated with VEC and δ to establish quantitative composition-property relationships.