Synergistic hardening and rotational mechanism of the multiscale heterogeneous structure in the (CoCrNi)90Al10 medium-entropy alloy

Designing heterogeneous structures is a proven strategy to overcome the strength–ductility trade-off in metallic materials by introducing additional hetero-deformation-induced (HDI) hardening. However, the quantitative differences in HDI hardening arising from various types of heterogeneity, as well as their respective dominant roles during deformation, remain poorly understood. In this work, a multiscale heterogeneous structure was engineered in a (CoCrNi)90Al10 medium-entropy alloy to reveal the distinct HDI hardening contributions of lamellar and hierarchical grain structure. The resulting alloy exhibits significantly enhanced tensile properties, attributed to the synergy of two rotation-mediated hardening mechanisms. Specifically, the lamellar architecture, composed of deformed grains and recrystallized micrometer-sized grains, provides pronounced HDI hardening at the early stage of deformation due to a higher density of hetero-interfaces. As deformation progresses, hierarchical grains, formed via dynamic grain refinement within the recrystallized regions, gradually dominate the heterogeneous deformation behavior. This is driven by the increasing fraction of fine micrometer grain interfaces and the higher accumulation of geometrically necessary dislocations at these boundaries. This study not only elucidates the distinct hardening mechanisms of lamellar and hierarchical hetero-structures but also offers some guidance for the rational design of high-performance structural alloys.