Superb strength-ductility synergy in a medium-entropy CoCrNi alloy via reinforced TRIP effect

In this study, a thermodynamically metastable medium-entropy Co37Cr34Ni29 (at.%) alloy exhibiting superior strength-elongation synergy at ambient temperature was fabricated successfully via tailoring the processing route. It was discovered that after homogenizing and hot-rolling processes, the microstructure of the alloy was composed of two-type face-centered-cubic (FCC)-structure phases: Co-type FCC structure (metastable) phase and Ni-type FCC structure (stable) phase. During the tension process, the metastable Co-type FCC-structure phase has transformed gradually into Co-type hexagonal close-packed (HCP)-structure phase in a restrained environment characterized by the formation of networks of nano-spacing HCP phase bundle. This kind of transformation could provide intensified transformation-induced plasticity (TRIP) effect during the plastic straining process, thus, the alloy presented superior strength-elongation synergy (UTS × TE > 88 GPa%) compared with other ductile FCC-structure alloys with TRIP effect.