Optimizing Al content to eliminate the brittle phase in lightweight TiZrNbTa_0.1Al_x refractory high-entropy alloys Available to Purchase

Body-centered cubic (BCC) lightweight refractory high-entropy alloys (LWRHEAs) with Al contents have attracted much attention due to their low density and excellent mechanical properties. However, these typical lightweight alloys often suffer from poor room temperature plasticity. In this study, we prepared TiZrNbTa_0.1Al_x LWRHEAs by using a high-vacuum arc-melting technique and investigated the influence of Al content on the phase structures and mechanical properties. It was found that the TiZrNbTa_0.1Al₁ alloy showed a BCC solid solution matrix with some micrometer-sized Al₃Zr₅ precipitates and exhibited a density of 6.110 ± 0.003 g/cm³. The TiZrNbTa_0.1Al₁ alloy had a low mixed enthalpy of −20.831 kJ/mol, a compressive yield strength of 1037 ± 178 MPa, and a fracture plasticity of ∼6%. As a result of reducing the Al content, the TiZrNbTa_0.1Al_0.2 alloy showed a simple BCC phase structure without any precipitates and maintained a low density of 6.743 ± 0.008 g/cm³. The TiZrNbTa_0.1Al_0.2 alloy had a relatively high mixed enthalpy of −4.5577 kJ/mol, a high yield strength of 1022 ± 51 MPa, and a plasticity of >70%. The TEM analysis results demonstrated that the excellent mechanical properties of this LWRHEA were mainly attributed to the reducing Al content, which could elevate the mixed enthalpy of the alloy to eliminate the brittle Al₃Zr₅ phase and induce the formation of dense network dislocations at the grain boundaries.