Achieving ultrahigh cryogenic yield strength and sufficient ductility in a medium-entropy alloy via bimodal grain design

This work proposes an efficient strengthening and toughening method. A CrCoNi medium-entropy alloy (MEA) with a bimodal grained structure can be designed by controlling intermediate-temperature-annealing after cold rolling. The bimodal grained MEA consists of ultrafine-grained domain and fine-grained domain (volume fractioñ37%), showing an ultrahigh yield strength (YS) of 1600 MPa and a remarkable uniform elongation of 19% at cryogenic temperature, whose cryogenic YS improves by ∼2.5 times compared to that of coarse-grained counterpart. The inhomogeneity of the bimodal grained structure can significantly improve the YS while maintaining stable strain hardening ability, and activate multiple deformation mechanisms including significant dislocation activities, massive stacking faults, deformation nanotwins, and Lomer-Cottrell locks. Our results demonstrate that tailoring bimodal grained structures can enrich the applications of MEAs in cryogenic engineering.