Feedstock powder preheating effects on the mechanical and microstructural characteristics of single-track laser powder-directed energy-deposited thin-wall AISI 316L structure morphology

Laser powder-directed energy deposition enables near-net-shape fabrication of components using focused laser energy. In this study, a feedstock powder preheating technique was implemented to evaluate the mechanical and morphological characteristics. Initially, preheating temperatures of 55, 65, and 75 °C were applied for single-track investigation. Optimal performance was observed at 65 °C, resulting in improved geometry and a microhardness value of 204 HV (clad), indicating enhanced bonding and consolidation. A thin-wall structure fabricated using the optimized parameters was characterized in the bottom, middle, and top regions. The bottom region of the fabricated thin-wall structure exhibited peak ultimate tensile strength and yield strength of 664.99 and 461.47 MPa, respectively, which decreased by about 3% and 13% toward the top region, while elongation increased from 29.7% to 34.2%. The maximum Vickers hardness of 455.8 HV and Rockwell hardness of 45.08 HRC were observed in the top region. Optical microscopy identified epitaxial growth with columnar dendrites in the bottom zone, whereas the middle and top zones mainly exhibited columnar dendrites. Scanning electron microscopy fractography confirmed ductile fracture with dimple morphology, and energy-dispersive X-ray analysis provided microstructural insights. X-ray diffraction analysis confirmed a dominant γ-Fe austenitic phase, and atomic force microscopy revealed increased surface roughness from the bottom to the top region.