Fabrication of spherical Ti-V-Zr-Nb-Mo-Hf-Ta-W refractory high-entropy alloy by a combination of spark plasma sintering, cryogenic grinding, and plasma centrifugal atomization

In this study, plasma-assisted centrifugal atomization was used to produce spherical powders of a refractory high-entropy alloy (R-HEA) with particle sizes within 50–250 µm, a median particle size by weight of 163 µm, and average chemical composition of Ti 12 V 15 Zr 5 Nb 15 Mo 17 Hf 5 Ta 16 W 15 . The powdered feedstock material for the atomization process was produced by a combination of partial solid-state consolidation of elemental powders by spark plasma sintering and cryogenic grinding, thereby eliminating the need for complex hydrogenation-dehydrogenation pulverization operations. The resulting spherical powder with particle sizes within 150–180 µm consisted of a main BCC-structured solid solution incorporating all principal elements, and trace amounts of FCC-structured Hf x Zr 1-x N precipitates. The microindentation hardness of the centrifugally atomized spherical powder was as high as 7.0 ± 0.3 GPa, approximately 30 % higher than that of previously reported R-HEAs with similar compositions and larger atomic size mismatch. The enhanced mechanical performance was attributed to the refined dendritic microstructure, with primary dendrite arms and interdendritic spacing of around 2 µm and 0.3 µm in thickness, respectively. These results suggested that high configurational entropy alone was not the cause for the superior mechanical properties of HEAs, and demonstrated that the grain boundary strengthening through microstructure refinement was a powerful tool to achieve outstandingly high hardness for such single-phased metallic alloys. The reported processing route showed promising potential for the pilot- and large-scale fabrication of spherical powders of R-HEAs for additive manufacturing purposes such as electron beam melting (EBM), laser metal deposition (LMD), and laser cladding (LC). • Pre-alloying by spark plasma sintering as an alternative to arc-melting of ingots. • Hydrogenation-dehydrogenation pulverization is replaced by cryogenic grinding. • Spherical powders of TiVZrNbMoHfTaW are prepared by plasma centrifugal atomization. • The spherical powder is 30 % harder than previous R-HEAs with similar compositions. • Structure refinement plays a greater role than high entropy on the microhardness.