Achieving superior combined cryogenic strength and ductility in a high-entropy alloy via the synergy of low stacking fault energy and multiscale heterostructure

A Co30Cr20Fe18Mn18Ni11Si3 high-entropy alloy (HEA) with low stacking fault energy and high strengthen was designed based on the principle of heterostructure strengthening. The alloy was processed into a multiscale heterogeneous microstructure containing hierarchical twins. The alloy achieved an ultrahigh yield strength of 1500 MPa, ultimate tensile strength of 1750 MPa and a large ductility of 20 % at 77 K. These mechanical properties were superior to those of most FCC HEAs reported in the literature, breaking the strength-ductility trade-off of conventional metal alloys. Such extraordinary mechanical properties were attributed to a suitable strain hardening capability, stemming from the synergistic effect of hetero-deformation-induced hardening, twinning-induced plasticity, and deformation-induced phase transformation during tensile deformation.