Additive Manufacturing just published our article Microstructure and corrosion properties of sensitized laser powder bed fusion printed Inconel 718 to dissolve support structures in a self-terminating manner. This shows that the original etching process we developed for stainless steel translates well to nickel alloys.
Abstract: This manuscript expands the existing framework for single-material laser powder bed fusion printed dissolvable supports to Inconel 718 (IN718). Prior work with stainless steel leveraged a sensitization heat treatment using sodium hexacyanoferrate to precipitate chromium carbides over the top 100 μm to 200 μm of material, decreasing the corrosion resistance within this top layer relative to the bulk material. The component is then etched at an anodic potential with a high selectivity toward the “sensitized” surface over the base component material. This creates an etching process that self-terminates once the sensitized layer is removed. Since supports are typically less than 200 μm thick, they are completely sensitized and dissolved. Additionally, the surface roughness of the component is often improved once the sensitized region is removed. In this work, two different sensitization heat schedules were investigated: 750 °C for 24 h to understand the impact of preferential chromium carbide precipitation and 1050 °C for 8 h to understand the impact of primary carbide precipitations. At 1050 °C, the formation of a protective oxide scale inhibits material removal in an electrolyte of 0.48 M HNO3. At 750 °C, 70 μm of material is removed after quenching to avoid the precipitation of corrosion resistant oxides. This manuscript investigates the effect of targeting different carbide precipitation regimes and oxides to produce an ideal microstructure for dissolvable supports post-sensitization. To demonstrate the utility of the process, the supports from a mock IN718 turbine blade were removed using this process.