The intrinsic mechanical properties of NbTaTiZr and the influence of alloying elements Mo and W: A first-principles study

Abstract

The intrinsic mechanical properties of NbTaTiZr and NbTaTiZrX (X Mo, W) are studied by using a first-principles calculation in combination with special quasi-random structure. For NbTaTiZr RHEA, the ideal tensile strength (ITS) and compressive strength (ICS) along [001] direction is respectively calculated to be 5.64 GPa and −18.4Gpa at the strain 11% and −20%. For shear loading along (211)[111] slip system, the ideal shear strength (ISS) is 3.03 GPa as the strain is about 20%. With addition of Mo into NbTaTiZr, the ITS, ICS and ISS respectively increase up to 9.7, −19.3 and 4.73 GPa, and the addition of W enhances the ITS, ICS and ISS up to 10.5, −21.1 and 5.12 GPa, respectively. Hence addition of Mo or W can significantly improve the ideal strength, especially stronger impact of W element. The calculated elastic moduli E [001] and G [111] are in reasonable agreement with the initial slope of the stress-strain relationship. The derived dimensionless ITS and ISS from first-principle calculations is underestimated the ideal strength in comparison with the prediction by the universal empirical model. Then the microcosmic mechanism is further studied by examination of the detailed bond length variation of three HEAs during the corresponding deformation. Near the critical strain under of tension and shear, the slower descend of stress originates from the gradual breakage of atomic bonds, while the compressive stress decreases rapidly owing to all bond fracturing almost simultaneously. Finally, the ideal strength of three HEAs is further analyzed from electronic structure. • The ideal strength is studied using ab initio calculations based on special quasi-random model. • The ideal strength and critical strain show NbTaTiZr has good strength and ductility. • The dimensionless ideal strength is overestimated in the empirical model. • The slow descend of tensile/shear stress results from the gradual breakage of atomic bonds. • The rapid decrease of compressive stress is due to the almost simultaneous fracture of all bonds.