Characterization Of Coating Failures Using Ion Beam Milling And High Resolution Energy Dispersive X-Ray Spectroscopy (C2026-00242)

Ville saarimaa, Markus Virtanen, Kaisa Laurila

Organic coatings are susceptible to degradation due to humidity, UV light or other variations in the atmosphere. The performance of color coated (or prepainted) steel in corrosive environments is conventionally assessed visually (degree of blistering, delamination) or by color and gloss measurements. However, the root cause of product failures is seldom revealed with these techniques. Recently, major leaps have been taken in cross-section preparation and sample characterization, facilitating coating failure root cause determination. Broad ion beam milling in vacuum has emerged as an alternative to conventional epoxy mounting, carbon coating and SEM imaging procedures, offering facile preparation of high-quality cross-sections without smearing or dissolution of delicate corrosion products. Combined with element mapping using a novel annular EDS detector, the “hidden” interfaces within coatings and early-stage degradation phenomena can be successfully observed. The annular EDS detector is capable of mapping < <100 nm features, including pigments, inclusion and small cavities within coatings. In this paper, the power of these tools is demonstrated through industry samples from various exposures.