Unravelling phase evolutions in gas atomized CoCrFeNiTi high-entropy alloy powders

In the CoCrFeMnNi ‘Cantor’ high-entropy alloy (HEA), the substitution of Mn with the larger atomic radius element Ti, together with the rapid cooling rates achieved through gas atomization, results in intriguing phase transformations. This study presents a comprehensive microstructural analysis of gas atomized CoCrFeNiTi HEA powders, along with an evaluation of their nano-hardness properties. The predominantly spherical and homogeneous powders feature dendritic/interdendritic solidification, with Cr and Fe concentrating in the dendrites, while Ni and Ti segregate into the interdendrites. In contrast, Co shows more uniform distribution throughout the powders. Within the dendrites, two distinct phases—tetragonal σ and rhombohedral R—are identified, as their lattice structures undergo symmetry modifications due to elemental distributions and lattice distortions. In addition, the interdendritic region contains B2, B19' (or a variant), and R phases, displaying martensitic transformations. Exhibiting remarkable nano-hardness performance, this HEA feedstock holds significant potential for manufacturing technologies such as thermal spray. • Intriguing phase transformations occur in gas atomized CoCrFeNiTi powders. • Symmetry variations are observed in the lattice structures of σ and R phases. • B2, B19' (or a related variant), and R phases lead to martensitic transformations. • Gas atomized CoCrFeNiTi powders show excellent nano-hardness properties.