Effect of Al on microstructure and mechanical properties of lightweight AlxNb0.5TiV2Zr0.5 refractory high entropy alloys

AlxNb0.5TiV2Zr0.5 (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) refractory high entropy alloys were prepared by vacuum arc melting to obtain a lightweight REHA with excellent microstructure and mechanical properties. The microstructure, density, hardness, and compressive properties at room and elevated temperatures of AlxNb0.5TiV2Zr0.5 alloys were investigated. All AlxNb0.5TiV2Zr0.5 alloys are composed of the BCC phase and the C14-Laves phase, and the volume fraction of the Laves phase raises from 12.03% to 22.83% and then decreases slightly to 20.31% with the increase of Al content. The density of AlxNb0.5TiV2Zr0.5 alloys decreases with the increase of Al content from 6.12 g/cm3 to 5.43 g/cm3, and the microhardness increases from 397.2 HV to 641.9 HV. At room temperature, the yield strength of AlxNb0.5TiV2Zr0.5 alloys increases obviously at first and then decreases slightly with the range of 843 MPa–1727 MPa. The compressive strain of the alloys obviously decreases from 33.4% to 13.7% at first and then increases to 16.6%. Upon increasing the temperature to 873 and 1073 K, the strength of all alloys decreases, and the yield strength of the Al0.8 alloy remains 1569 and 1108 MPa, respectively. The compression ratios of all AlxNb0.5TiV2Zr0.5 alloys reach 50% without fracture at this temperature. The specific yield strength of Al0.8 alloy acheives 312 × 103, 284 × 103, and 199 × 103 MPa·cm3g-1 at 298, 873, and 1073 K, which is superior to that of other alloys. A strong correlation between the mechanical properties and the Al content of AlxNb0.5TiV2Zr0.5 alloys is observed. Al is one of the elements that can promote the formation of the Laves phase, and the volume fraction of the Laves phase increases with the increasing Al content. As a hard intermetallic compound phase, the mechanical properties of the alloys are improved with the increasing volume fraction of the Laves phase.