Comparative Study of Micro- and Nano-structured Coatings for High-Temperature Oxidation in Steam Atmospheres
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For many high-temperature applications, coatings are applied in order to protect structural materials against a wide range of different environments: oxidation, metal dusting, sulphidation, molten salts, steam, etc. The resistance achieved by the use of different kind of coatings, such as functionally graded material coatings, has been optimized with the latest designs. In the case of supercritical steam turbines, many attempts have been made in terms of micro-structural coatings design, mainly based on aluminides, and other diffusion coating systems in order to consider alternatives, nano-structured coatings based on Cr and Al compositions and deposited by a physical vapor deposition technique, were assessed to high-temperature oxidation resistance in steam environments. The oxidation kinetics where analyzed for up to 2,000 h at 650 °C by means of gravimetric measurements. The evaporation behavior was also analyzed by thermogravimetric-mass spectrometry. Excellent results where observed for some of the nano-structured coatings tested. Those results where compared to results obtained for micro-structured coatings. Based on that comparison, it was deduced that the nano-structured coatings have a potential application as protective systems in high-temperature steam environments.
KeywordsSteam oxidation Nano-structured coatings CrAlN coatings FeAl coatings
The present work was supported by the Spanish Ministry of Science and Technology, projects ENE2008-06755-C02-02 and CONSOLIDER CSD2008-00023. Dr. R. Escobar Galindo acknowledges financial support through Ramon y Cajal Spanish programme (RyC2007-0026). The authors would like to thank to TEKNIKER and Inasmet research centers at the Basque Country in Spain to provide the nano-structured coated samples.
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