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This project seeks to develop the use of computed tomography (CT) for inspection of metallic AM parts by investigating the current state-of-the-art to scan deliberately flawed parts.
Additive manufacturing (AM) has many advantages when compared to traditional subtractive manufacturing processes for fabrication of low-volume, high-value, complex shaped parts. Capitalizing on the advantages of AM can allow performance enhancements, weight reduction, cost reduction, and decrease production time of the parent product. However, quality control issues must be adequately addressed prior to widespread utilization. One of the key challenges is nondestructive inspection of AM fabricated components. Non-destructive evaluation (NDE) techniques are needed to validate the AM process performance. Flaws and cavities containing unused powder are unique to the powder-bed fusion AM processes and can make flaw detection more difficult. The lack of adequate NDE techniques for inspection of AM-produced parts was identified as one of the main current challenges to the use of AM. Recent AM roadmaps have identified and assigned high priority to: (1) surveying, selecting, and adapting current NDE technologies; (2) searching for new modalities; and (3) validating and transitioning of NDE to AM component inspection.
The goal of this project is to assess x-ray computed tomography (CT) performance in detection and sizing of typical AM flaws and nonconformances in titanium- and nickel-based alloys produced using AM. The project objectives include: (1) identify and select complex aerospace components for NDE analysis; (2) determine the size and shape of embedded, fabricated flaws that can be created in the AM build process; (3) build the selected components using Direct Metal Laser Melting (DMLM) and Electron Beam Melting (EBM) AM processes; (4) conduct x-ray CT of these AM-built components; and (5) assess the x-ray CT performance in detection and sizing of the embedded flaws and typical AM nonconformities. Information gathered during the project will expand available data about x-ray CT quantitative limits for detection of discontinuities in complex geometries.
Aerospace components with desired complexity suitable for AM fabrication and of interest to the AFRL will be selected. A study will be done to incorporate designed flaws into Inconel 718 and Titanium 6Al-4V coupons to determine achievable flaw shapes and sizes using various techniques, creating both surface and subsurface flaws. CT modeling and simulations will be done to estimate flaw detection capabilities using the geometries and materials of the selected components. The selected parts will then be fabricated with the identified, designed flaws of various shapes and sizes using DMLM and EBM processes. Components will be post-processed using typical part and material-based thermal treatment plans. Following fabrication, NDE will be performed on the components using x-ray CT testing several CT parameter sets followed by metallographic destructive characterization to determine how actual flaw dimensions compare to the generated CT data. Results will be analyzed to assess the x-ray CT performance in detection and sizing of implanted flaws, as well as other fabrication nonconformities.