Compositional effect on microstructure and mechanical properties of AlNbTiZr-based refractory high entropy alloys

This study aims to investigate the phase composition, microstructure, and mechanical properties of three refractory high-entropy alloys (RHEAs): Al7(NbTiZr)93, Al7(NbTiZrMo)93, and Al7(NbTiZrTa)93. The as-cast Al7(NbTiZr)93 alloy exhibits a single-phase BCC structure, with a yield strength (YS) of 1050 MPa at room temperature. The addition of Mo and Ta leads to the formation of Al7(NbTiZrMo)93 and Al7(NbTiZrTa)93 alloys with BCC-B2 and B2-FCC dual-phase structures, whose YS values reach 1741 MPa and 2350 MPa, respectively. At 800 °C, trace amounts of ordered B2 phase are generated in the Al7(NbTiZr)93 matrix, and the YS decreases from 1050 MPa at room temperature to 219 MPa at 800 °C. In the Al7(NbTiZrMo)93 alloy, the 10 nm B2 precipitates grow to several hundred nanometers, and the YS decreases to 431 MPa after compression at 800 °C. In the Al7(NbTiZrTa)93 alloy, the grid B2-FCC structure at room temperature transforms into a disordered BCC structure at 800 °C, yet possessing the YS of 908 MPa and demonstrating acceptable ductility. Moreover, Ta exhibits the better structural and performance matching than Mo in AlNbTiZr-based RHEAs. Therefore, it opens up new prospects for regulating the structure and high-temperature performance of AlNbTiZr-based RHEAs.