Improving the strength and ductility of laser directed energy deposited CrMnFeCoNi high-entropy alloy by laser shock peening

Abstract

In this study, laser shock peening (LSP) was employed to change the stress state and microstructure of the surface layer of CrMnFeCoNi HEA fabricated by laser directed energy deposition (LDED) and improve its mechanical properties. The surface morphology, residual stress, and tensile properties of the CrMnFeCoNi HEA with and without LSP were investigated. Furthermore, we characterized the microstructure evolution of the specimen treated by LSP along the depth direction before and after conducting a tensile test. Results indicated that LSP transformed the surface-stress state from tensile to compressive stress, and the pores in the surface layer were closed after undergoing severe plastic deformation. Additionally, LSP resulted in the development of a gradient microstructure along the depth direction. The formation of a sandwich structure with a hardened surface layer and soft core improved the strength and ductility of the specimens treated by LSP. The underlying mechanisms that improved the strength and ductility were proposed.