Heterogeneous-Structured Refractory High-Entropy Alloys: A Review of State-of-the-Art Developments and Trends

Refractory high-entropy alloys (RHEAs) inspire the development of novel high-temperature structural materials due to their outstanding resistance to softening and phase stability at elevated temperatures. However, they struggle to simultaneously achieve high-temperature strength and room-temperature ductility, while exhibiting insufficient room-temperature strain hardening capability. Heterogeneous structure strengthening possesses a unique plastic self-coordinated ability, which can effectively maintain strain hardening rate to achieve an excellent combination of strength and ductility. Benefiting from slow atomic diffusion, severe lattice distortion, and broad compositional design space, RHEAs with heterogeneous structures can be prepared from both chemical composition and interface structure perspectives. Chemical composition heterogeneity primarily focuses on fluctuations of alloying elements at the nanoscale, along with the formation of heterogeneous precipitates and unique lamellar eutectic structures. While, interface structure heterogeneity manifests in the activation of phase transformation and twin boundaries within grains, along with the formation of grains of vastly different sizes. The trend in RHEAs development is toward structural-functional integration. Heterogeneous structures can also optimize functional properties, such as irradiation resistance, biomedical properties, and high-temperature softening resistance of RHEAs. Finally, a brief outlook is provided on the future development direction of heterogeneous structure RHEAs. This review summarizes the latest advances in optimizing the mechanical properties and functional characteristics of refractory high-entropy alloys through heterogeneous structure strategies. It provides a comprehensive overview of compositional and structural heterogeneity at different scales, offering valuable insights for the design of advanced refractory high-entropy alloys with integrated structural and functional properties. image