Modulated Structure Formation in Dislocation Cells in 316L Stainless Steel Fabricated by Laser Powder Bed Fusion

Metal additive manufacturing enables producing complex geometric structures with high accuracy and breaks the design constraints of traditional manufacturing methods. Laser powder bed fusion, a typical additive manufacturing process, presents a challenge in experimentally understanding the nano-scaled microstructure-process relationship regarding the wide range of process parameters. In this study, we aim to reveal the novel nanoscale structural features by advanced scanning transmission electron microscopy to clarify the formation mechanisms in 316L stainless steel by laser powder bed fusion. Here we show that the slender columnar grains were confined to the centreline of the melt pool along the build direction, and the columnar cell structure at the side branching of the melt pool grew along orthogonal directions to follow drastic changes in thermal gradient across adjacent melt pools. Novel nano-scaled modulated structures have been observed in the dislocation cells parallel to the laser scan direction, which were mainly caused by the elastic strain involving the thermal gradient inside the melt pool and across adjacent melt pools as well as the effective strain field in the dislocation cell interiors. An in-depth understanding of microstructure developments is worthy of fabricating high-performance materials by controlling the additive manufacturing process. [doi:10.2320/matertrans.MT-ME2022004]

Automated summary

Metal additive manufacturing allows for the production of complex geometric structures with high accuracy, overcoming the limitations of traditional manufacturing methods. Laser powder bed fusion, a common additive manufacturing process, poses challenges in understanding the nano-scale microstructure-process relationship. In this study, advanced scanning transmission electron microscopy was used to reveal novel nanoscale structural features in 316L stainless steel produced by laser powder bed fusion. The findings demonstrate the confinement of slender columnar grains to the centerline of the melt pool, and the growth of columnar cell structures along orthogonal directions at the side branching of the melt pool. Novel nano-scaled modulated structures were observed in dislocation cells parallel to the laser scan direction, resulting from elastic and effective strain fields. This study provides important insights for fabricating high-performance materials through controlled additive manufacturing.