Use of isotopic tracers and SIMS analysis for evaluating the oxidation behaviour of protective coatings on nickel based superalloys

In this investigation, the oxide growth mechanisms of a Pt-alummide type coating were investigated using a two-stage oxidation treatment. The samples are first oxidised in unlabelled O-16(2), followed by a second oxidation in O-18(2) enriched tracer gas. Oxygen diffusion characteristics through the oxide scale were determined by SIMS depth profiling. Focused ion beam analysis was also conducted using a Ga+ ion beam to mill cross-sections and then perform elemental mapping. Encouraging results have been obtained from this series of experiments and have clearly shown the two different oxidation mechanisms that occur at temperatures above and below approximately 1000 degreesC which are associated with the formation of theta and alpha alumina scales. (C) 2002 Elsevier Science B.V. All rights reserved.