Achieving ultra-high strength in a precipitation-hardened CoCrNi-based medium-entropy alloy with partially recrystallized microstructure and heterogeneous grains

A η*-Ni₆(Al,Ti)Nb strengthened CoCrNi-based medium-entropy alloy with partially recrystallized and heterogeneous grain microstructure was prepared. Block and lamellar η*-Ni₆(Al,Ti)Nb phases were present in different regions. Excellent tensile properties were achieved with yield strength of 1.34 GPa, ultimate tensile strength of 1.55 GPa and ductility of 9.2%. The deformation mode was dominated by stacking faults in all grains at the beginning of deformation and then relied on dislocation slip in the recrystallized grains. The high strain hardening rate is due to the intense obstruction effect of the η*-Ni₆(Al,Ti)Nb phase for dislocation movement and the hard-deformed non-recrystallized grains. Our findings provide a wider range of options for the selection of the precipitation phase.