Fabrication and Process Monitoring of 316L Stainless Steel by Laser Powder Bed Fusion with µ-Helix Scanning Strategy and Narrow Scanning Line Intervals
Yuheng Liu, Kazufumi Nose, Masayuki Okugawa, Yuichiro Koizumi, Takayoshi Nakano
Abstract
We first fabricated the single crystal of 316L stainless steel by laser powder bed fusion (L-PBF), focusing on the applicability of the µ-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 µ-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.