Microstructure, corrosion resistance and wear properties of laser directed energy deposited CrCoNi medium-entropy alloy after cyclic deep cryogenic treatment

Subjected to repeated heating and cooling, laser directed energy deposited (LDED) parts always possess considerable residual stress, which severely limits their industrial applications. In this work, cyclic deep cryogenic treatment (CDCT) was performed to finely tune the residual stress and microstructure of LDED-fabricated CrCoNi medium-entropy alloy (MEA). With increasing number of CDCT cycles, crystalline defects within the sample became denser due to the repeated visco-plastic deformation. The compressive residual stress (CRS) of the sample was estimated to be 361.9 ± 16.8 MPa after 30 cycles of CDCT, 64.2% higher than that in the as-built condition. Due to the existence of dense crystalline defects and high CRS, the corrosion and wear rates of CDCT-treated CrCoNi MEA were significantly decreased compared with the as-built condition. This work demonstrated CDCT as an effective means for regulating the residual stress, microstructure, and surface performance of LDED-fabricated MEA.