Several crucial issues remain unanswered despite extensive attempts to establish relationships between process parameters, microstructure, and properties of materials produced via additive manufacturing. In particular, many studies have shown that microstructure features, such as cell structure, that are typical of laser powder bed fusion (L-PBF), result in the high strength. Yet, it remains unclear where these features originate from and how they correlate with crystallography. 

The term “cell structure” originates from the studies of conventional materials: during plastic deformation, a three-dimensional dislocation cell structure forms, and its pattern is orientation dependent. During the solidification stage of the L-PBF process, the solidified material also undergoes plastic deformation as a result of thermal shrinkage. Therefore, in the present work, we investigate the cell structure in single track L-PBF samples. By using single track, the complexity involved with repeated heat and melt cycles can be avoided, making it easier to understand the cell structure formation mechanisms and the possible effects of crystallographic orientation. 

Detailed material characterisation of single track L-PBF 316L samples is conducted in this work. Scanning Electron Microscope is used to visualize the morphology of grains and cell structure, and Electron Backscatter Diffraction is used to correlate crystallographic orientations with the dislocation cell structure. In addition, multilayer single track samples are also investigated to evaluate possible effects of constraints on cell structure observed in the single track study. To gain a better knowledge of the microstructure in three dimensions of L-PBF 316L stainless steel, both transverse and longitudinal cross-sections are analysed. Based on the experimental results of single and multiple track samples, the origin and pattern of cell structure in bulk L-PBF samples are discussed.