Support Thickness, Pitch, and Applied Bias Effects on the Carbide Formation, Surface Roughness, and Material Removal of
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https://doi.org/10.1007/s11837-020-04422-y 2020 The Minerals, Metals & Materials Society
ADDITIVE MANUFACTURING FOR ENERGY APPLICATIONS
Support Thickness, Pitch, and Applied Bias Effects on the Carbide Formation, Surface Roughness, and Material Removal of Additively Manufactured 316 L Stainless Steel ROBERT HOFFMAN ,1 SHAWN HINNEBUSCH,2 SUBBARAO RAIKAR,1 ALBERT C. TO,2 and OWEN J. HILDRETH 1,3 1.—Department of Mechanical Engineering, Colorado School of Mines, 1500 Illinois St, Golden, CO 80401, USA. 2.—Department of Mechanical Engineering and Materials Science, University of Pittsburgh, 4200 Fifth Ave, Pittsburgh, PA 15260, USA. 3.—e-mail: [email protected]
Advances in self-terminating etching processes have brought dissolvable supports to selective laser-melted stainless-steel alloys. Preliminary data showed that the amount of support material removed could be larger than the amount of material removed from the bulk material. This article details a small study aimed at understanding this phenomenon. First, the material removed and roughness as a function of applied bias is studied. From this, two different potentials were selected, 400 mVSHE, which removes 120 lm through intergranular corrosion, and 550 mVSHE, which removes material 39 lm through uniform corrosion. Next, a simulated set of support structures with wall thicknesses varying from 82 lm to 544 lm was etched under these two different potentials to report the range of thicknesses that can be reasonably removed.
INTRODUCTION Post-processing metal components fabricated using laser powder bed fusion (L-PBF) additive manufacturing (AM) technologies present a significant challenge that both restricts design freedom and increases costs.1 This is especially true for components with internal supports or internal features that are difficult to access using mechanical grinding methods traditionally used for AM component post-processing. To address this issue, the Hildreth group recently introduced a self-terminating etching technique that brings dissolvable supports to L-PBF metals.2 This process, schematically illustrated in Fig. 1, begins by printing the components using existing equipment and printing parameters. Next, the component with attached supports and any trapped powder is immersed in an aqueous solution of saturated sodium hexacyanoferrate [Na4Fe(CN)6Æ10H2O] and allowed to dry, coating all surfaces with a layer of sodium hexacyanoferrate. The component is then put through (Received July 9, 2020; accepted September 26, 2020)
the standard post-print heat treatment commonly used to remove residual stresses and refine the microstructure. The sodium hexacyanoferrate decomposes during this process to form a layer of surface carbon that then diffuses into the component’s surface, where it captures the passivating chromium in chromium carbide precipitates. This reduction in free chromium ‘‘sensitizes’’ this region and reduces the corrosion potential, Ecorr, below that of the stainless steel.3 The sensitized component is then etched under conditions th
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