Mechanical properties and oxidation behavior of NbMoTaWx refractory high entropy alloys

NbMoTaW refractory high-entropy alloys (RHEAs) possess superior high-temperature mechanical strength. However, their practical applications are limited by low room-temperature plastic strain. In the present study, NbMoTaWx (x = 0.2, 0.4, 0.6, 0.8, 1.0) RHEAs were prepared. The microstructural characteristics, mechanical properties and oxidation resistance of these RHEAs were investigated. The NbMoTaWx RHEAs were all single-phase solid solutions. With the addition of W content, the yield strength, density and hardness of the alloy gradually increased, and the grain size decreased. Notably, a significant improvement in the compressive ductility of the investigated NbMoTaWx RHEAs was observed. The highest mechanical strength (1712 MPa) and ductility (10.6%) were exhibited by NbMoTaW0.4. Fracture surfaces indicate the alloy fractured along the grain. The W can be solidly dissolved in the Nb and Ta oxides, altering the structure of the oxide to impede the entry of oxygen and slow down the rate of oxidation. The increase of W enhanced the oxidation resistance of the alloys.