Fabrication and Process Monitoring of 316L Stainless Steel by Laser Powder Bed Fusion with ?-Helix Scanning Strategy and Narrow Scanning Line Intervals

We first fabricated the single crystal of 316L stainless steel by laser powder bed fusion (L-PBF), focusing on the applicability of the mu-Helix scanning strategy with narrow pitch as a method for obtaining a single crystal. Various combinations of laser power and laser scanning speed were examined. The cubic block samples were orientated to <100> in the X-laser scanning direction, to <110> in the Y-laser scanning direction, and to <110> in the building direction, which is contrary to that obtained by the mu-Helix scanning strategy in electron beam melting (EBM), in which the X-and Y-laser scanning directions are orientated to <110>, and Z-direction is oriented to <100> direction. Also, it has been demonstrated that melt pool monitoring by on-axis and off-axis dual photodiodes can detect the nonequivalence of +/- X-scanning and +/- Y-scanning, which is responsible for the unexpected crystal orientation.