Additive manufacturing (AM) describes an array of methods used to create a 3D object layer by layer. The increasing popularity of AM in the past decade has been due to its demonstrated potential to increase design flexibility, produce rapid prototypes, and decrease material waste. Temporary supports are an inconvenient necessity in many metal AM parts. These sacrificial structures are used to fabricate large overhangs, anchor the part to the build substrate, and provide a heat pathway to avoid warping. Polymers AM has addressed this issue by using support material that is soluble in an electrolyte that the base material is not. In contrast, metals AM has traditionally approached support removal using time consuming, costly methods such as electrical discharge machining or a dremel.

This work introduces dissolvable supports to single- and multi-material metals AM. The multi-material approach uses material choice to design a functionally graded material where corrosion is the functionality being varied. The single-material approach is the primary focus of this thesis, leveraging already common post-print heat treatments to locally alter the microstructure near the surface. By including a sensitizing agent in the ageing heat treatment, carbon is diffused into the part decreasing the corrosion resistance to a depth equal to at least half the support thickness. In a properly chosen electrolyte, this layer is easily chemically, or electrochemically removed. Stainless steel 316 (SS316) and Inconel 718 are both investigated to study this process using two popular alloys. The microstructure evolution and corrosion properties are investigated for both. For SS316, the effect of applied electrochemical potential is investigated to describe the varying corrosion phenomena induced, and the effect of potential choice on resultant roughness. In summary, a new approach to remove supports from metal AM parts is introduced to decrease costs and further the field of metals AM by expanding the design space.

Additive Manufacturing and 3D printing are becoming important technologies in the manufacturing sector. The benefits of this technology include complex part geometry, short lead-times, low waste, and simple user interface. However, the technology does not come without its drawbacks: mainly the removal of support structures from the component. Traditional techniques that involve sawing and cutting can be expensive and take a long time, increasing the overall price of 3D printed metal components. This paper discusses two approaches taken for dissolvable support structures in 3D printed stainless steel (17-4 PH). For the first time in powder bed fusion components, with the help of Christopher Lefky and Dr. Owen Hildreth, dissolvable support capabilities are achieved in metal prints. The first approach, direct dissolution, involves direct corrosion of the entire part, leading to support removal. This approach is not self-terminating, and leads to changes in final component geometry. The second approach involves a post-build sensitization step, which physically alters the microstructure and chemical stability of the first 100-200 microns of the metal. The component is then etched at an electric potential that will readily corrode this sensitized surface, but not the underlying base metal. An electrolytic solution of HNO3/KCl/HCl paired with an anodic bias was used for the direct dissolution approach, resulting in a loss of about 120 microns of material from the components surface. For the self-limiting approach, surface sensitization was achieve through a post build annealing step (800 C for 6 hours, air cooled) with exposure to a sodium hexacynoferrate slurry. When the slurry decomposes in the furnace, carbon atoms diffuse into the surface and precipitate a chromium-carbide, which reduces the chemical stability of the stainless steel. Etching is demonstrated in an anodic bias of HNO3/KCl. To determine proper etching potentials, open circuit potential and cyclic voltammetry experiments were run to create Potentiodynamic Polarization Curves. Further testing of the self-terminating approach was performed on a 316 stainless steel interlocking ring structure with a complex geometry. In this case, 32.5 hours of etching at anodic potentials replaced days of mechanical sawing and cutting.