Microstructure evolution of IN718 wire with SS316L powder co-deposited using laser directed energy deposition

This study investigates the evolution of bead geometry, microstructure, and elemental segregation during the co-deposition of Inconel 718 (IN718) wire and 316 L stainless steel (SS316L) powder using coaxial wire-powder laser-directed energy deposition. A systematic experimental approach is employed, progressing from single-layer single-track to single-layer multi-track, and subsequently multi-layer multi-track configurations to evaluate process scalability and stability. The influence of laser power, scan speed, powder feed rate, hatch spacing, and layer height on deposition geometry, chemical mixing, and defect formation is analyzed using optical and electron microscopy techniques. The results demonstrate that appropriate laser power – scan speed parameter selection is essential to achieve homogeneous mixing between IN718 wire and SS316L powder. Solidification cracking mechanisms associated with Nb-rich microsegregation are demonstrated to follow a consistent interdendritic path through Electron Dispersive X-Ray Spectroscopy elemental maps. While powder addition locally refines dendritic structures and promotes columnar grain partitioning, unfused particles act as nucleation sites that exacerbate defect formation under unstable processing conditions. These findings highlight the critical role of geometric and material input parameters in controlling lack-of-fusion (LoF) defects through improved track overlap. Moreover, the results reveal that as the process transitions to multi-layer configurations, thermal accumulation and repeated remelting dominate defect formation, leading to a shift from LoF to crack-driven mechanisms.