Mechanical properties of refractory high-entropy alloys: Experiments and modeling

Abstract

Refractory high-entropy alloys hold the potential for high-temperature applications beyond the capability of the state-of-the-art Ni-based superalloys, and thus, it is important to study their solid solution formation characteristics and mechanical properties. In this study, designed by CALPHAD method, formation of as-cast arc-melted body-centered cubic MoNbTaTiV was experimentally verified using X-ray diffraction and scanning electron microscopy. The measured density and lattice parameter for MoNbTaTiV are 9.29g/cm3 and 3.224 Å, which obey the rule of mixtures (ROM). The alloy exhibits high hardness at 443 Hv, high yield strength at 1.4 GPa, and good compressive fracture strength at 2.45 GPa with a fracture strain of ∼30% at room temperature. The yield strength and hardness values of this alloy, and other single-phase refractory high-entropy alloys, are estimated using a simple model of solid solution strengthening. Reasonable agreement between modeling prediction and experiments is obtained. In addition, first-principles density functional theory calculations predict an enthalpy of formation of −0.865 kJ/mol for the MoNbTaTiV alloy, with calculated atomic volume and elastic properties (e.g., bulk and elastic moduli) obeying the ROM.