Synergistic Optimization of Strength and Plasticity for Low-Activation (TiVZrTaWx)100‒yNy Refractory High-Entropy Alloys

Abstract:

Refractory high-entropy alloys (RHEAs) usually exhibit high strength but limited plasticity at room temperature. Their strength enhancement depends on the mechanisms such as lattice distortion and solid-solution strengthening, which restrict dislocation motions and thus reduce their plasticity. In contrast, the strengthening mechanisms that improve plasticity often weaken strengthening effect. Therefore, enhancing both strength and plasticity simultaneously remains a significant challenge for RHEAs. To address this issue, TiVZrTaW_x (x=5, 10, 15, 20) low-activation RHEAs were designed and prepared, and the effects of W content on the phase structure, microstructure, and compressive mechanical properties were investigated. The results show that increasing the W content to 10% can enhance both the strength and plasticity simultaneously, and the TiVZrTaW₁₀ RHEA shows a hardness of 535.7 HV, a yield strength of 1808.85 MPa and a plasticity of 7.22%. Such improvement is mainly attributed to the solid-solution strengthening and secondary-phase strengthening effects. To further enhance the mechanical properties, a minor amount of N was added to the TiVZrTaW₁₀ RHEA. The results show that the strength and plasticity of the (TiVZrTaW₁₀)_100?yN_y RHEAs are further improved. The typical (TiVZrTaW₁₀)_98.5N_1.5 RHEA exhibits a hardness of 605.8 HV, a yield strength of 2008.66 MPa, and a plasticity of 11.25%. Through TEM and other analyses, the enhanced mechanical properties are found to mainly result from the secondary-phase strengthening, synergistic deformation of the matrix and secondary phases during compression, and interstitial strengthening effects induced by N addition.