Microstructure, mechanical properties and incipient plasticity of (Ti42.5Zr42.5Nb10Ta5)100-xMox refractory high-entropy alloys

Abstract

A series of (Ti42.5Zr42.5Nb10Ta5)100-xMox (x = 0, 3, 5 and 7 at.%) refractory high-entropy alloys (RHEAs) were prepared, and the influence of Mo content on microstructure and mechanical properties of the RHEAs were systematically studied. All the RHEAs consist of a single body-centered cubic (BCC) phase. As the Mo content increases from 0 at.% to 7 at.%, the yield strength of RHEAs increases from 670 MPa to 975 MPa at room temperature. The high strength of the BCC RHEAs mainly depends on solid-solution strengthening caused by the Mo addition. The RHEAs with low Mo content (0–5 at.%) can possess high tensile plasticity of ∼20 %, while it reflects brittle after the 7 at.% Mo addition. The high tensile plasticity of the RHEAs was attributed to the combined effects of lattice rotation to promote and refine crystalline strengthening. The RHEAs with 5 at.% Mo addition have high specific yield strength (∼32 MPa g−1cm3) and excellent fracture strains (＞60 %) at 1173 K. Moreover, the incipient plasticity of the RHEAs was analyzed by nanoindentation. It is shown that the maximum shear stress (τmax) of the RHEAs from 1.80–2.34 GPa to 2.67–4.83 GPa. The activation volumes (v∗) of the RHEAs from 0.7 Ω to 1.1 Ω. The nanomechanical properties of the RHEAs are related to the Mo content. The purpose of this work is to design RHEAs with excellent mechanical properties and to offer a theoretical foundation to assist new RHEA design.