Microstructure and mechanical properties of MoNbVTa0.5Alx refractory high entropy alloys

The specific strength of refractory high entropy alloys (RHEAs) is usually impaired due to the high density of constituent elements. In order to develop a low-density RHEA, the microstructure and mechanical property of MoNbVTa0.5-based RHEAs with various Al additions have been investigated in this study. All samples exhibited a monolithic BCC solid solution structure. The addition of Al resulted in improved yield strength but a degraded plasticity at ambient temperature. In contrast, the yield strength consistently decreased with increasing Al content at elevated temperatures, and the softening occurred at ∼1000 °C. MoNbVTa0.5Al0.3 exhibited high specific strengths of 119.2 MPa cm3/g, 108.6 MPa cm3/g and 97.3 MPa cm3/g at 600 °C, 800 °C, and 1000 °C, respectively. •MoNbVTa0.5Alx RHEAs were designed with lower density and compositional segregation.•Doped Al improves yield strength at ambient temperature due to solid solution strengthening.•Doped Al degrades the thermal stability with more pronounced thermally activated flow.•Doped Al improves the specific strength at elevated temperatures with obvious lightening effect.