Dissolvable Supports in Powder Bed Fusion-Printed Stainless Steel

This work demonstrates, for the first time, two approaches for dissolvable supports in powder bed fusion-printed metal parts. Expanding on our recent innovations with dissolvable supports in multimaterial direct energy deposition printing, this work brings dissolvable support capabilities to additive manufacturing systems that are limited to single-material builds. First, a direct dissolution approach is demonstrated with the supports electrochemically dissolved. While this process works, it is not self-terminating and maintaining dimensional accuracy for complex geometries is thus difficult. The second approach incorporates a sensitizing agent during the normal stress, relieving thermal annealing step to decrease the chemical stability of the top 100–200 μm of the component surface. The component is then etched under etching conditions 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. These two processes are first demonstrated using 17-4 PH stainless steel. Direct dissolution was conducted under anodic bias in a solution of HNO3/KCl/HCl; 120 μm of material were removed from the component's surface. For the self-terminating dissolution process, surface sensitization was done by exposing the sample to sodium hexacyanoferrate at 800°C for 6 h to carburize the top 100–200 μm of the sample. This carburization process captures the protective chromium in chromium carbide precipitates and renders the surface sensitive to chemical and electrochemical dissolution. The self-terminating etching reaction was demonstrated under anodic bias in a solution of HNO3/KCl. Open circuit potentials were measured at 10 s and 1 h, and polarization curves were used to identify the corrosion potential. Self-termination was verified by monitoring component diameter over time, and 120 μm of material were removed from the sensitized surface of the component. To further test the self-terminating sensitized approach, a set of 316 stainless steel interlocking rings were fabricated to demonstrate that this approach scales to large components with complex geometry. For these parts, this approach replaced 4–5 days of machining operations with a 32.5 h electrochemical bath.