A new approach to online thickness measurement of thermal spray coatings

In the past 10 years, significant progress has been made in the field of advanced sensors for particle and spray plume characterization. However, there are very few commercially available technologies for the online characterization of the as-deposited coatings. In particular, coating thickness is one of the most important parameters to monitor and control. Current methods such as destructive tests or direct mechanical measurements can cause significant production downtime. This article presents a novel approach that enables online, real-time, and noncontact measurement of individual spray pass thickness during deposition. Micron-level resolution was achieved on various coatings and substrate materials. The precision has been shown to be independent of surface roughness or thermal expansion. Results obtained on typical high-velocity oxyfuel and plasma-sprayed coatings are presented. Finally, current fields of application, technical limitations, and future developments are discussed. This article was originally published inBuilding on 100 Years of Success: Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.