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2001 |
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Wednesday, May 05, 2010, Hullet Room 11:20 AM Corrosion Protection |
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Phase composition and microstructural responses of crystalline mullite/YSZ coating under water vapor environments |
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Eugenio Garcia / Instituto de Ceramica y Vidrio (CSIC), Spain Joana Mesquita-Guimaraes / Institute of Ceramics and Glas (CSIC), Spain Pilar Miranzo/ Institute of Ceramics and Glas (CSIC), Spain Maria Isabel Osendi*/ Institute of Ceramics and Glas (CSIC), Spain Cristian Cojocaru/ National Research Council of Canada, Canada Youliang Wang/ National Research Council of Canada, Canada Christian Moreau/ National Research Council of Canada, Canada Rogerio Lima/ National Research Council of Canada, Canada |
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Some early works have shown that mullite and mullite /ZrO2 systems can be considered as environment barrier coatings (EBCs) for protection of Si-based (Si3N4, SiC) substrates against water vapor corrosion for application in forthcoming turbine engines. In addition, composite mullite/Y-ZrO2 intermediate layers can be tailored to reduce the coefficient of thermal expansion mismatch between both layers on top of the expected strengthening effect of the t-ZrO2 phase in the composite. In this study, single mullite coatings and a bi-layer system composed by a layer of mullite and a top layer of mullite/ Y-ZrO2 (75/25 wt%.) were plasma sprayed over Hexoloy SiC substrates. The feedstock materials were porous granulates processed by two different routes to examine the influence of the powder characteristics on the coatings performance. To reduce cracking associated to crystallization issues, highly crystalline as-sprayed coatings were engineered. The single and bi-layer coatings were furnace heat-treated at 1300 ºC in a controlled water vapor environment during 100 h. The effect of these corrosion tests on the coatings was comparatively investigated, putting special emphasis in determining crystalline phases changes by using X- ray diffraction (XRD) and differential thermal analysis (DTA) tools. The microstructures of as-sprayed and exposed coatings were intensively studied by scanning electron microscopy (SEM) and correlated with the results obtained by XRD and DYA analysis. |