Achieving ultrahigh strength in CoCrNi-based medium-entropy alloys with synergistic strengthening effect

Here, we report a novel CoCrNiAl0.1MO0.1 medium entropy alloy, which possessed a complex structure comprising with the non-recrystallized structure, recrystallized structure, fine grains and precipitate phase. The alloy displayed exceptional tensile properties after cold-rolled and annealing at various temperatures in a range of 725-900 degrees C. As annealed at 725 degrees C, the alloy exhibit a tensile strength of 1304 MPa, and uniform elongation of 22% due to the synergistic strengthening of the high density of dislocation in the non-recrystallized regions, ultrafine grains and precipitates in the recrystallized structure. As annealing increasing, further growth of recrystallization region and grain size, resulting in high ductility but low strength. The alloy achieves excellent strength-ductility combination by adjusting microstructure (degree of recrystallization, sizes of grain and precipitate phase, etc.) at different annealing temperature. These results offer an extremely effective design strategy to enhance strength-ductility trade-off by simple thermal treatment.