Evaluating deposits of SS316L powder and wire consolidated using co-axial laser directed energy deposition

Abstract

The direction in which wire and powder feedstock are fed influences deposit quality of as-built parts produced using laser-direct energy deposition (L-DED). While lateral wire feed has been explored in existing L-DED investigations, limitations like process instability persist, especially in achieving the required connection between the wire and the melt pool. Co-axial feedstock deposition offers a potential solution, enabling higher manufacturing flexibility and efficiency by co-axially feeding wire or powder. However, the full potential of L-DED using co-axial feeding for metal components remains underexplored due to equipment limitations. This study systematically evaluates the printability of stainless steel (SS) 316L and compares the microstructures and microhardness properties between co-axial powder-fed and wire-fed L-DED specimens. Utilizing the MELTIO M450 L-DED system in an argon environment, single-layer three-track specimens are produced with different combinations of process parameters. Comprehensive characterization, employing optical and scanning electron microscopy alongside microhardness testing, reveals powder-fed specimens exhibit greater melt pool depth and cooling rates, while wire-fed counterparts display fewer oxide inclusions and smoother surfaces. Microstructural differences include higher δ-ferrite content in wire-fed specimens. Microhardness values between powder-fed and wire-fed specimens are comparable. These findings hold implications for sequential powder and wire deposition, enabling the production of diverse mechanical structures with distinct characteristics. Overall, this paper provides an insight into feedstock selection for efficient metallic part production via co-axial feedstock deposition and recommends a range of process parameters suitable for fabricating SS316L parts using co-axial deposition in L-DED.