Revisiting the role of prestrain history in the mechanical properties of ultrafine-grained CoCrFeMnNi high-entropy alloy

The yield strength of face-centered cubic (FCC) alloy is always insufficient for applications. In this work, different prestrain histories were imposed to improve the yield strength and strain-hardening capability of an ultrafine-grained (UFG) CoCrFeMnNi high-entropy alloy (HEA). In contrast to the specimens prestrained at 293 K, the specimens prestrained at 77 K possess higher yield strength, elongation, and strain-hardening capability, which were intensely related to the formation of deformation twins. The cryogenic strengthening magnitude is found to be strongly associated with the grain size, but slightly affected by dislocations. By modulating the prestrain history, an ultrahigh yield strength of 1.84 GPa and a considerable uniform elongation of 13% were achieved at 77 K in the CoCrFeMnNi HEA. Hence, imposing prestrain on HEAs at 77 K could be an efficient strategy to harmonize the mechanical properties of the FCC HEAs, which would enrich the application of HEAs in cryogenic fields.