Superior tensile properties and formability synergy of high-entropy alloys through inverse-gradient structures via laser surface treatment

Heterostructuring is an emerging method for achieving an excellent combination of strength and ductility; however, its usage is often limited in the industry because of poor formability. The high mechanical incompatibility between domains in heterostructured materials facilitates crack initiation and propagation during forming. To broaden the industrial applicability of heterostructured materials, it is necessary to balance their tensile properties and formability. Herein, we propose a new strategy for designing heterostructures that are optimized for non-uniform deformation during forming. Cold-rolled CoCrFeMnNi high-entropy alloy sheets were laser treated on both sides to fabricate an inverse-gradient structure (soft outer and hard inner regions) with superior strength-ductility synergy. Furthermore, the inverse-gradient samples exhibited excellent bendability because the outer coarse-grained region prevented the generation of external cracks, and the decrease in the strength difference between neighboring domains reduced the damage evolution. Consequently, the present heterostructured high-entropy alloys exhibit superior tensile properties and formability.