High-temperature creep-oxidation interaction of (VNb)₈₀(TaTi)₂₀ refractory high-entropy alloy

The tensile creep behavior of the refractory high-entropy alloy (VNb)₈₀(TaTi)₂₀ is investigated at elevated temperatures (1023–1123 K) under the applied stresses ranging from 200 to 400 MPa and a relatively low vacuum condition of 1 × 10⁻² Pa. The creep behavior at 1073 K follows a power law, with a stress exponent of 3.0 ± 0.4 and an activation energy of 283 ± 13 kJ mol⁻¹, indicating a solute drag mechanism, which is also evidenced by the dispersed dislocations without entanglements. The fracture surfaces of the post-creep specimens display brittle intergranular cracking, resulting from the significant oxidation during the creep test. A surface oxide layer forms rapidly and continues to thicken, accompanied by grain boundary oxidation and internal oxidation. These processes induce surface degradation, stress concentration, and weakening of grain boundaries, thereby accelerating localized creep deformation. Conversely, creep deformation disrupts the oxide layer, generates fresh surfaces that enhance oxygen diffusion, and promotes further localized oxidation. This synergistic interaction between creep and oxidation results in premature intergranular fracture and material failure, which eventually leads to reduced creep life and lower creep strain in the (VNb)₈₀(TaTi)₂₀ alloy. Nevertheless, this alloy still outperforms major reported RHEAs with its low steady-state creep rates under the present testing conditions, demonstrating a superior creep resistance. These findings provide a valuable insight into the creep mechanisms and oxidation-coupled deformation behavior of (VNb)₈₀(TaTi)₂₀, offering important guidance for the design of advanced refractory high-entropy alloys with improved creep resistance and oxidation stability.