Assessment of Paint Layers by FE-SEM and EDS Examination

Report No. ARL-TR-3232
Authors: Donovan Harris
Date/Pages: June 2004; 38 pages
Abstract: Three painted aluminum panels were examined to verify total coating thickness and to determine the thickness of each coating layer. The approach was to remove free-film samples from each panel, fracture the films, and then examine at high magnification the cross sections using a field emission-scanning electron microscope (FE-SEM). The initial film removal method was not successful. It was decided to back-score a section of each panel and then freeze-fracture a whole segment. The FE-SEM micrographs confirmed the thickness measurements made earlier using an Elcometer. The observed morphology of each coating film was consistent across the entire thickness, and no layering could be determined. Energy dispersive spectroscopy was used to analyze each film and then map the elemental distributions across each film thickness. The use of quantitative elemental mapping showed the actual chemical distributions and indicated the presence of two distinct layers. On each panel, one layer accounted for a minimum of about two-thirds of the total thickness of the paint film, but both layers were the epoxy primer. No discrete chromate layer was detectable.
Distribution: Approved for public release
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Last Update / Reviewed: June 1, 2004