Ultrahigh cryogenic strength and exceptional ductility in ultrafine-grained CoCrFeMnNi high-entropy alloy with fully recrystallized structure

Abstract

Similar to the conventional alloys, attaining excellent combination of high strength and ductility is still challenging in the high-entropy alloys (HEAs). In this work, a fully recrystallized ultrafine-grained (UFG) microstructure was introduced into the single-phase CoCrFeMnNi HEA via cold rolling and annealing process. The UFG HEA displays ultrahigh yield and ultimate tensile strengths of 1.24 GPa and 1.46 GPa, respectively, and excellent ductility with a uniform elongation of 41% at 77 K. The exceptional strength-ductility combination in the UFG CoCrFeMnNi HEA surpasses those of all existing HEAs and other advanced engineering alloys. Such unparalleled mechanical properties stem from the fully recrystallized ultrafine grains that significantly strengthen the material and simultaneously provide high strain-hardening capability and the activations of multiple deformation mechanisms consisting of prominent dislocation activities, profuse stacking faults, and deformation twins. The fully recrystallized UFG microstructures do not only shed light on the design and development of HEAs with superior mechanical properties, but also enrich the potential applications of HEAs at the cryogenic environment.