Superior high-temperature strength in a dual-BCC-phase NbMoTaWHf refractory high-entropy alloy

High-temperature structural alloys are urgently desired for refractory applications. In this work, we conceived a facile route to achieve an excellent combination of high-temperature strength and room-temperature ductility in a NbMoTaWHf refractory high-entropy alloy (RHEA). The idea is to break up the stable single body-centered cubic (BCC) phase in NbMoTaW RHEA to introduce the tiny secondary phase by alloying appropriate hafnium (Hf) that can stall and accumulate dislocations. The dual-BCC-phase structure and the dislocations for the NbMoTaWHf RHEA were characterized. The compressive yield strengths of the NbMoTaWHf RHEA at room temperature, 1200, 1600, and 1800 °C were 1730, 1088, 390, and 312 MPa, respectively. The alloy displayed plastic deformation behaviors and dual-BCC-phase structure stability after compressing at 1600 and 1800 °C. The superb high-temperature strength was mainly ascribed to the high softening temperature, second-phase strengthening, and solid-solution strengthening. This work provides a promising high-temperature structural material with improved room-temperature ductility and high strength at elevated temperatures and enriches the database of the NbMoTaW-based RHEAs.