On the Role of Spraying Process on Microstructural, Mechanical, and Thermal Response of Alumina Coatings
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. Costil, C. Verdy, R. Bolot, and C. Coddet (Submitted February 27, 2007; in revised form June 7, 2007) Thermal spraying is a widely used technology for industrial applications to provide coatings that improve the surface characteristics. According to the specificities of processes (APS, VPS, flame, electric arc), any kind of material can be sprayed. Among materials, ceramic coatings present several interesting aspects such as wear resistance, corrosion protection as well as thermal or electrical insulation; particularly alumina coatings which appear as the most commonly used. From all spraying processes, atmospheric plasma spraying (APS) is a rather well-established process but some others can also be used with a lower economical impact such as the flame technology. The aim of this study was to analyze the alumina coating properties according to the technology employed such as APS or wire flame spraying using the RokideÔ and the Master JetÒ guns. After micrographic analyses by SEM, physical and mechanical properties were measured considering the thermal conductivity and the hardness.
Keywords
alumina coating, APS, coating characteristics, flame spraying, microstructure, SEM
1. Introduction Thermal spraying is a widely used technology in a large range of industrial applications to provide coatings that improve the surface characteristics. Whatever the technology used, the principle is always similar consisting in injecting the selected material (powder, wire, rods) into an area of high temperature where it is melted, accelerated, and directed onto the substrate surface (Ref 1, 2). According to the thermal and kinetic specificities of all processes (APS, VPS, flame, electric arc), all material types can be sprayed provided their melting temperature is at least 300 K lower than their vaporization or decomposition temperature. Among materials, ceramic coatings present several interesting aspects such as wear resistance, corrosion protection as well as thermal or electrical insulation and particularly alumina coatings which appear as the most commonly used. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 1416, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007. S. Costil, C. Verdy, R. Bolot, and C. Coddet, LERMPS-UTBM, 90 010 Belfort cedex, France. Contact e-mail: sophie.costil@ utbm.fr.
Journal of Thermal Spray Technology
Many techniques can also be used to spray such kind of materials. Among them, Atmospheric Plasma Spraying (APS) is rather well-established as a commercial process for the deposition of alumina coatings. However, despite the coating microstructures which present typical aspects like inter lamellar micro cracks, unmolten particles, por
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