Fabrication of multi-gradient heterostructured CoCrFeMnNi high-entropy alloy using laser metal deposition

Abstract

Heterostructured materials have superior strength–ductility behavior than conventional homogenous materials. In this study, a multi-gradient heterostructured CoCrFeMnNi high-entropy alloy (HEA) was fabricated through laser metal deposition (LMD) on highly deformed (∼84% cold-rolled) equiatomic CoCrFeMnNi HEA sheets. The microstructure of the prepared CoCrFeMnNi HEA comprises four regions—a coarse-grained region, transition region, fine-grained region, and partially recrystallized region—that have different mechanical properties owing to different heat inputs. This new class of heterostructured material shows a significantly enhanced strength–ductility performance at both 298 K and 77 K compared to conventional additively-manufactured CoCrFeMnNi HEA. The combination of the partially recrystallized region, which has a high yield strength, and the fully recrystallized regions, which have high strain hardenability and elongation, provides superior mechanical performance through additional back stress strengthening. This study proposes a new method to manufacture multi-gradient materials by direct LMD on rolled plates, unlike conventional gradient structuring methods that require a post-process on annealed plates.