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Surface Finishing of Additive Manufactured Nickel-Based Superalloys Liquid Rocket Channel Nozzles

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  • location_onMcCormick Place
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  • schoolIntermediate

The extreme surface roughness characteristic of AM components is a common topic of discussion. AM-built components typically present many surface/near-surface defects that affect their mechanical properties and performance. Nevertheless, if planned accordingly, a suitable surface finishing operation can eliminate these surface-related defects (SRDs), significantly improving their mechanical properties. However, since most of these SRDs are located within 0.02" (0.5mm) from the surface, the components need to be built with extra amounts of sacrificial material to allow for the surface finishing operation. Moreover, the surface finishing technique must be capable of removing this amount of metal in a fast and uniform way. This presentation will showcase the three surface finishing processes known to date, capable of efficiently removing 0.02" from the surface of AM components built out of nickel-based superalloys (NBS). Dog-bone test specimens made from NBS, built by powder bed fusion and direct energy deposition, were surface finished by different processes: chemical milling, electropolishing, chemically-accelerated vibratory finishing and a combination of these processes in different orders. A full characterization of the specimens before and after the finishing operation will be presented, including micro X-ray CT-scans, and surface texture profiles. Additionally, mechanical testing of tensile and fatigue stress (high and low-cycle) will be presented for each of the surface finishing operations, in order to establish the impact of each one of these surface finishing technologies on the mechanical performance of the specimens. Finally, remarkable results from the processing of an NBS-AM rocket nozzle in collaboration with NASA will be shown.

Learning Objectives:

  • Understand the benefits of surface finishing (post-processing) and the impact that it has on mechanical performance
  • Understand the mechanism of the most widely used mass-finishing operations specifically designed for AM produced parts
  • Determine which surface finishing technology will be suitable for different applications and how to plan for it before building