Effect of energy density on the interface evolution of stainless steel 316L deposited upon INC 625 via directed energy deposition

Directed energy deposition (DED) is an additive manufacturing technique that permits the manufacturing of complex multi-material components. In the present study, DED was used for the fabrication of Inconel 625 and stainless steel 316L couples. The effect of input energy density on the evolution of the dissimilar metal interface and its mechanical properties was explored by varying the laser power for each build. Columns that transitioned directly from Inconel 625 to stainless steel 316L were deposited onto mild steel substrates. The columns were cross-sectioned and characterised by coupling physical characterisation with microhardness. Scanning electron microscopy and compositional mapping were used to correlate the relationship between energy density and the produced functional gradient. It was seen that high energy deposition resulted in a measurable, remelted layer solute (RLS) fraction that comprised each deposited layer, creating a stepwise-graded interface. The RLS fraction was consistent across each layer of the interface and was influenced by the energy density of the build. Changes in the RLS affected the length of the graded interface but did not have a significant influence the mechanical properties. The yield strength and ultimate tensile strength of the through-interface compared well with the traditional wrought stainless steel 316L but suffered in ductility. Mix-mode fracture tended to occur in the near stainless steel composition regions.