Abstract

Thermally-sprayed coatings are applied to various materials to provide protection for beat-loaded parts as well as corrosion and wear. They also serve as a thermal barrier to reduce metal substrate temperatures. Microstructural analysis is used to characterize the substrate, the coating, and the adherence of the coating to the substrate. Accurate evaluation or these coatings depends heavily upon the quality of the polished surface produced by metallographic preparation. A well-prepared surface must first be free of plucked material and have minimal relief between the hard and soft constituents. The entire surface must be flat to allow a clear view of the interface and any reaction products that might be present in the coating or the substrate. Furthermore, the finished polished specimen must be scratch-free and have no resolution destroying films or stains. Various metal and oxide coatings on ferrous substrate material are used to demonstrate the excellent microstructural detail that is revealed when correct polishing procedures are used. These special techniques successfully address the problems normally encountered when preparing hard, brittle coatings or softer metallic coatings and substrates. As a result, clear microstructures are revealed across the specimen surface and valuable information is obtained.

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