Mechanical and microstructural properties of 316LSi stainless steel manufactured via laser-directed energy deposition with rear lateral wire material feeding

Abstract

Abstract Directed energy deposition with wire feeding (L-DED-wire) provides manufacturers with higher production rates and lower initial costs compared to powder bed fusion techniques. However, direct deposition exposes the material to relatively more extreme thermal gradients and a less protective atmosphere. Subsequently, the microstructure and mechanical properties of the processed metal can be more sensitive to manufacturing parameters. Accordingly, this study investigates 316LSi stainless steel processed via L-DED-wire to evaluate the parametric window and properties of the L-DED-wire and the processed metal, respectively. Two wall structures were manufactured using an industrial robotic setup with a continuous wave fiber laser and wire feedstock. Test samples were prepared and analyzed via quasi-static tensile testing (in both parallel and perpendicular orientations), scanning electron microscopy, Vickers hardness measurements, and surface roughness evaluation. The results indicate that due to irregular material accumulations, there is a higher possibility of defects such as lack of fusions, e.g., at the very end of deposited tracks. Also, parallel-oriented tensile specimens exhibited higher yield and ultimate tensile strengths than perpendicular ones, indicating the interlayer boundaries as the main weak points in the L-DED-wire component. The resultant microstructure was austenitic with hierarchical subgrain features and localized ferrite. The diversity in subgrain morphology and size, potentially driven by complex thermal gradients during deposition, was linked to local variations in Vickers hardness across sample cross-sections. The average surface roughness (Ra) of the as-built parts was 25 µm, which was in the range of other components made via direct deposition techniques per the literature.