Electropolishing to Surface Finish of Hastelloy X Manufactured By Laser Powder Bed Fusion

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Laser Powder Bed Fusion (LPBF) is a metal additive manufacturing technology (AM) that uses high power laser to melt powder layer by layer to create mechanical parts. LPBF several advantages, including short manufacturing time, freedom to design complex geometries and user-friendly customization. It is widely used in the manufacture of high-value parts in aerospace, automotive and biomedical industries. Due to the nature of the layer-by-layer process, partially melted powder is attached to the as-built part surface during LPBF, resulting in a significant increase in surface roughness. Furthermore, initial surface roughness of final part is different with locations since quantity of powder adhesion varies depending on building angle. Increase of surface roughness due to attached metal powder can cause out of dimensional tolerance that designed. Such dimensional inaccuracy can lead to failure or breakage of the mechanical parts. Therefore, surface post-treatment is essential to reduce surface roughness with minimizing dimensional change. Conventional mechanical and chemical treatments for surface finishing have limitations such as limited tooling range and surface damage due to the use of strong acids and long-time of processing. Electropolishing, based on electrochemical reactions, is suitable for improving the roughness of LPBF manufactured parts with complex geometries. Thickness reduction can be predicted by controlling the applied voltage and processing time. Also, surfaces in contact with the electrolyte is polished without geometric restrictions. Studies have been reported that analyze the change in surface roughness after electropolishing to improve the roughness of alloys manufactured with LPBF. However, for application to real parts, it is necessary to conduct basic research to optimize the electropolishing conditions to obtain satisfactory surface roughness with minimal thickness reduction by considering the effect of dimensional changes during electropolishing. In this study, we electropolished Hastelloy X fabricated by LPBF. Four types of electrolytes were selected for electropolishing. We measured surface roughness and thickness reduction with respect to applied voltage and processing time. With such results, optimized condition to reduce the surface roughness with minimal thickness changes are discussed. Then, these conditions were applied to LPBF specimen with different building angles. Surface roughness and weight changes were measured to compare polishing efficiency to each electrolyte.