Bimodal Microstructure Design of CrMnFeCoNi High-Entropy Alloy Using Powder Metallurgy

Abstract

Single-phase equiatomic high-entropy alloy (HEA); CrMnFeCoNi, exhibits high strength and ductility at room temperature and low temperature due to the effect of twinning. In this study, a concept of a bimodal microstructure design for HEA using powder metallurgy was proposed. Microstructures of the sintered compact fabricated from HEA powder mechanically-milled using SUJ2 balls were analyzed by EBSD. A network structure of fine grains (Shell), which surrounded the coarse-grained structure (Core), was formed in the HEA compact. The hardness of the HEA with bimodal microstructure were higher than the compact fabricated from as-received HEA powder, and the network structure showed high hardness than Core phase. Furthermore, W-rich surface layer was formed on the HEA powder mechanically-milled using WC-Co balls owing to the transfer of WC-Co balls to the surface of HEA powder during mechanical milling. A network structure of the W-rich phase, which surrounded the HEA phase, was formed in the compact fabricated from the mechanically-milled HEA powder. In particular, the hardness of compact fabricated from HEA powder mechanically-milled using WC-Co balls was high due to the high concentration of tungsten and formation of Shell phase. These results indicate that developed method can control the microstructure of HEA; grain size and elementary diffusion distributions.