Oxygen-assisted spinodal structure achieves 1.5 GPa yield strength in a ductile refractory high-entropy alloy

Refractory high-entropy alloys (RHEAs) with room-temperature ductility are drawing growing attention for potential high-temperature applications. However, the most widely used metallurgical mechanisms appear weak in optimizing their strength and ductility. Here, we report that the nanoscale spinodal structure in Ti₄₁V₂₇Hf₁₅Nb₁₅O₂ leads to the highest tensile yield strength (∼1.5 GPa) among the existing RHEAs and good elongation of ∼12%. With the aid of thermodynamic calculations, we show that oxygen plays a dominant role in controlling the formation of the spinodal structure by influencing the spinodal gap of the Ti-V-Hf-Nb system. Exploring the atomic structure of the spinodal structure (β + β*), we showed that the large lattice misfit of the spinodal phases is mainly responsible for the excellent strengthening effect while the planar to wavy dislocation glide mode transition accounts for the retained ductility. This work provides a novel strategy to improve the mechanical properties of the RHEAs and deepens the understanding of their phase stabilities.