Microstructural features induced by the Gaussian laser beam shape on 316L stainless steel thin-walled samples fabricated by directed energy deposition

Abstract The microstructure and mechanical properties of metallic parts produced by additive manufacturing are significantly influenced by processing parameters. For laser-based technologies, the laser beam shape introduces an additional variable, which can profoundly affect the crystallography orientation, microstructure, and phase composition of the final part. This study investigates the effects of a Gaussian laser beam profile on the microstructure and phase distribution in thin-walled 316L stainless steel samples fabricated by directed energy deposition (DED). Hollow cylinders fabricated with a single-bead deposition were cut in one position along the growth direction (YZ sample). Furthermore, additional cuts were performed in positions perpendicular to the building direction in order to extract two XY samples, one comprising the first deposited layers and the second one the final layers of the build job. Detailed characterization revealed that the Gaussian beam shape profile drives localized variations in phase composition, with a marked disparity in δ-ferrite content between the outer regions and the core of the walls. Furthermore, microhardness measurements along the printing direction indicate that lattice microstrain, rather than primary cellular arm spacing (PCAS), predominantly governs hardness levels.