Tailoring microstructures and mechanical properties of lightweight refractory Ti 22 Sc 22 Zr 22 Nb 17 V 17 multi-phase high-entropy alloys by hot extrusion and annealing

Lightweight refractory high-entropy alloys (LW-RHEAs) are promising candidates for high-temperature applications, which have become a research hotspot in materials community. In this work, the phase formation, microstructures, and mechanical properties of a lightweight Ti 22 Sc 22 Zr 22 Nb 17 V 17 multi-phase high-entropy alloy (HEA) fabricated by hot extrusion and annealing are investigated. Experimental observations show that the homogenized sample exhibits a relatively uniform microstructure containing body-centered-cubic (BCC), hexagonal closed-packed (HCP) and a few face-centered cubic (FCC) phases, while the HCP structures display two chemical compositions. The subsequent hot extrusion promotes the formation of hierarchical heterostructure which is composed of elongated coarse dendrites and extremely fine dynamically recrystallized mixtures. The BCC and FCC phases exhibit different morphologies and chemical compositions. Upon annealing, equiaxed BCC and HCP grains, slender BCC dendrites, and two types of FCC particles dominate the microstructures. Compared to reported refractory HEAs, the present alloys exhibit an good balance between elongation and specific strength. Compared with the homogenized sample, the strength of the hot-extruded sample is significantly improved, while annealing after hot extrusion induces larger ductility. The improved mechanical properties are attributed to grain boundary strengthening, precipitation strengthening, and the hierarchical heterostructure. The present studies are expected to open ever-bright prospects for fabricating high-performance lightweight HEAs.