Influence of blue laser-wire directed energy deposition parameters on the microstructure of SS316L

This Master’s Degree thesis investigates the optimization of printing parameters, specifically laser power and scanning speed, for the 316L stainless steel alloy processed by Laser Wire Directed Energy Deposition (LW-DED) using a blue laser source on a Meltio M600 system. LW-DED enables the fabrication of large-scale metallic parts, but a clear understanding of the relationship between processing conditions and microstructural evolution is still required. The study focuses on the influence of printing parameters on cooling rate, melt pool size, ferrite content, texture, porosity, and hardness. Microstructural characterization has been performed through optical microscopy and electron backscatter diffraction (EBSD), supported by quantitative porosity analysis. Results show that increasing laser power leads to higher porosity, with pore morphology shifting from elongated pores at low power to more equiaxed pores at higher power. Scanning speed was found to play a crucial role in defect formation, strongly influencing both the amount and distribution of porosity. Melt pool dimensions were strongly dependent on the power, directly affecting local thermal gradients and cooling rates. EBSD analysis revealed a deviation from the commonly reported <001>//BD texture, suggesting altered heat flow compared to powder-based processes. The microstructure was characterized by skeletal and lathy δ-ferrite, consistent with FA-type solidification. Ferrite quantification by EBSD aligned more closely with literature values than image analysis, highlighting EBSD’s superior accuracy for phase assessment. Overall, the findings show that laser power and scanning speed strongly influence defects, solidification, and texture in LW-DED 316L, providing valuable insights for process optimization and improved material performance.