Cryoforged nanotwinned CoCrNi medium-entropy alloy with exceptional fatigue property at cryogenic temperature

The extraordinary work hardening ability and fracture toughness of the face-centered cubic medium-entropy alloy (MEA) at cryogenic temperature make them good candidates for harsh applications. In this work, we developed a hierarchical twin architecture in coarse grained CoCrNi MEA using multidirectional cryoforging (MDCF) technique and low-temperature annealing. The unique substructure brought a notable enhancement in the cryogenic tensile strength-ductility balance, as well as an impressive 106-cycle fatigue strength of up to 1100 MPa at cryogenic temperature, which is superior to other cryogenic alloys. The exceptional fatigue property of MDCF-MEA is ascribed to the synergistic effect of high-density dislocations and a dense nanotwin/microband network, providing high strength and the ability to suppress local surface roughening and crack initiation. Our work demonstrates a practical route to further extend CoCrNi MEA for the cryogenic application.