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3941 |
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Wednesday, May 21, 2014, Hall H3 2:20 PM Power Generation - Industrial Gas Turbines 1 |
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Thermal sprayed Y2O3-Al2O3-SiO2 (YAS) coatings for environmental protection of SiC ceramics |
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Eugenio Garcia* / Instituto de Ceramica y Vidrio (CSIC), Spain Andres Nistal / Institute for Ceramics and Glass (ICV-CSIC), Spain M.Antonia Sainz/ Institute for Ceramics and Glass (ICV-CSIC), Spain M.Isabel Osendi/ Institute for Ceramics and Glass (ICV-CSIC), Spain Pilar Miranzo/ Institute for Ceramics and Glass (ICV-CSIC), Spain Federico Martín de la Escalera/ Aernnova Engineering Solutions Ibérica, Spain Amal Khalifa/ Aernnova Engineering Solutions Ibérica, Spain |
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Due to their good thermo-mechanical properties at high temperature, SiC-based composites are relevant for applications in the nuclear and aerospace industries, where high thermo-mechanical loads are common. However, the oxidation of these materials at temperatures above 500 °C confines their use to inert or vacuum environments. The loss of inherent properties caused by oxidation can be reduced or even eliminated by applying protective coatings. These coatings must fulfill several requirements, such as chemical and mechanical compatibility with the substrate, low oxygen permeability and thermal expansion coefficient close to that of SiC for reducing the level of residual thermal stresses. As a result, an environmental protection coating using some glass-forming compositions are envisioned as advantageous candidates for this application and most likely with the benefit of acting as crack healing agents at service temperature. In this work one composition located within the glass-forming region of the Y2O3-Al2O3-SiO2 (YAS) system is proposed and tested as compatible coatings for SiC. Glass samples of the selected composition were produced and granules -round shaped and uniform in composition- were prepared by spray drying of homogeneous powder mixtures of the selected YAS compositions. Coatings were fabricated by oxyacetylene flame spraying technique of the as-prepared granules on SiC substrates previously coated with a Si bond layer. The bulk glass samples and as-sprayed specimens were subjected to different thermal treatments to verify the nucleation of crystalline phases and the crack healing ability. The microstructural characteristics, mechanical and thermal properties of these materials were also investigated. |