Thermally Stable Heterogeneous-Grained Refractory High-Entropy Alloy Offering Superior Strength from 77 to 973 K

Achieving a robust strength-ductility balance across a wide temperature range remains a major challenge for refractory high-entropy alloys (RHEAs). In this study, we design a cold-workable NbTaTiHf-based RHEA with a thermally stable heterogeneous grain structure created through thermomechanical processing. This tailored microstructure enables exceptional mechanical performance, from cryogenic (77 K) to elevated temperatures (973 K), achieving tensile strengths exceeding 1.8 GPa at 77 K and maintaining over 900 MPa at 973 K. The primary mechanism responsible for this performance is a highly refined heterogeneous microstructure, which is rendered thermally stable even after extended annealing at high temperatures by the concentrated refractory elements that entail sluggish kinetics. As such, the hetero-deformation-induced (HDI) strengthening mechanisms can be maintained effectively even in high-temperature regimes. Our work offers a practical design approach for next-generation RHEAs with superior mechanical properties across a wide range of temperatures.