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MELD Aluminum Test Coupons and Neutron Interferometry Imaging

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Conference Abstract: Cross sections of MELD test coupons are, a priori, expected to show layering. However, conventional X-ray imaging does not show layering and conventional neutron transmission imaging only weakly shows layering. In contrast, neutron interferometry, particularly the modality called dark-field imaging or scattering imaging, shows a rich layered structure.

The Multimodal Advanced Radiography Station at Oak Ridge National Laboratory, High-Flux Isotope Reactor, CG-1D, has been used for two experimental neutron interferometry campaigns. The first campaign detected the layering and the second explored the layering as a function of MELD test coupons with normal and low graphite lubrication during the MELD fabrication. In addition, the MELD samples were post-processed with three different heat treatment procedures.

The neutron interferometry work inspired three follow-up experiments: 1) a preliminary residual stress analysis with the ORNL HIDRA beamline, 2) neutron Bragg-edge spectroscopy imaging, and 3) PFIB-SEM. These experiments are in progress and have the goal of testing the current hypothesis. The current hypothesis accounting for the neutron interferometry imaging structure also has the potential for increasing strength in the MELD structures.