Copper alloying to enhance the mechanical properties and oxidation resistance of ductile refractory high-entropy alloys

Refractory high-entropy alloys (RHEAs) are highly valued for their excellent high-temperature properties, and the enhancement of their room-temperature strength-plasticity matching and oxidation resistance is crucial for their processing and applications. In this study, the focus was on investigating the changes in the room-temperature mechanical properties and oxidation resistance of RHEAs when Cu was added to Ti₄₀Nb₄₀Ta₁₀Zr₁₀ RHEA with good strength-plasticity matching. The results show that the addition of Cu can form dispersed granular (Cu, Zr)-rich precipitation phases in RHEAs. These dispersed precipitated phases increase the tensile yield strength from ∼686 MPa to ∼870 MPa through a precipitation strengthening mechanism, and their interaction with dislocations during plastic deformation increases the uniform elongation from ∼1.9 % to ∼8 %, which in turn maintains the elongation at fracture at ∼16 %. In addition, the addition of Cu element also refines the dendrite size of RHEAs and increases the area of the interdendritic region that can easily react with oxygen, which in turn reduces the area of the oxide layer, and significantly enhances the oxidation resistance of RHEAs at 800 °C. These findings provide valuable insights for optimizing the strength-plasticity matching of RHEAs at room temperature and enhancing their oxidation resistance.