Comprehensive Analysis of Microstructure Evolution and Temperature Profiles in SS 316L during Laser-Based Directed Energy Deposition

The study investigated the multilayer laser-based direct energy deposition (L-DED) of SS 316L with an energy density of 72 J/mm. Laser power and scan velocity were fixed at 350 W and 4 mm/s, respectively. Study on the thermal behavior of SS 316L multilayer deposition, particularly the correlation between thermal cycles and microstructural properties, is limited. A 3D finite element thermal simulation reproduced thermal phenomena, including recurrent heating and cooling cycles, and provided temperature data correlated with microstructural morphology. Columnar grains and ferrite (δ) transition were observed, while XRD results indicated reduced carbide formation in the fusion zone with additional layers. The high-angle grain boundary (HAGB) fraction increased with layer deposition, aligning grains along <101> / < 001> in the second and third layers. Higher HAGB fractions improve strength by hindering dislocation motion. Texture analysis showed cube, rotated cube, and copper structures emerging with additional layers, favoring specific crystallographic orientations and influencing anisotropic mechanical properties.