Directed energy deposition on porous metal substrates: interfacial characteristics and process strategies for joining porous and dense structures

Porous metals combine low density with high energy absorption and thermal insulation, which makes them suitable for demanding structural applications such as crash-absorbing inserts in automotive components. However, to fully exploit their potential, reliable methods are needed to join these porous materials with dense structures to form hybrid porous components. Additive manufacturing technologies, like laser-based Directed Energy Deposition (DED-LB) offer the ability to manufacture various geometries and materials onto porous metals. In this study, DED-LB is used to deposit dense material layers on porous metallic substrates. The porosity was mimicked by drilling holes with defined geometry into 316L stainless steel substrates. To study the influence of different pore arrangements, the center-to-center distance between the holes was varied while keeping the pore geometry constant. Three process strategies were evaluated: laser remelting (LR) for smoothing the surface, direct DED-LB, and combinations thereof, with and without pre-filling the pores with loose powder prior to LR. Surface quality was quantified using the Pa profile parameter, while optical micrographs provided insight into process-material interaction and bonding of the deposited material to the porous substrate. The results show that LR significantly smooths the porous surface, with higher laser power yielding the lowest Pa values. DED-LB on porous surfaces leads to uneven material deposition and inconsistent bonding, particularly in regions with steep pore flanks. The combination of LR and DED-LB, especially with pre-filled pores, produced the smoothest surfaces and the most consistent material distribution. Despite thermal influence, no collapse of bridges to underlying pores was observed, which would deteriorate the surface quality. The optimized manufacturing strategy therefore shows great potential to realize hybrid porous components.