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

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.