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2731 |
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Thursday, September 29, 2011, Saal A 2:50 PM Aviation Industry 4 |
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Rare earth silicate coatings by sol precursor plasma spraying for environmental barrier applications |
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Aurelie Quet / CEA, DAM, Le Ripault, France Luc Bianchi*/ CEA, DAM, Le Ripault, France François Gitzhofer/ Université de Sherbrooke, Canada Jean-Luc Leluan/ Safran, Snecma Propulsion Solide, France Francis Rebillat/ Université Bordeaux 1, LCTS, France |
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Rare earth silicates are among the candidates for protection of silicon-based ceramics in high temperature and moist environments due to chemical and mechanical compatibility with substrate, low volatility and moisture resistance. Here we reported on the development of yttrium and ytterbium silicate coatings by sol precursor plasma spraying. The use of a sol feedstock allowed easy composition flexibility. The microstructure and the structure of as-sprayed and heat-treated coatings were investigated. Finer microstructure was obtained compared to micrometric powder plasma spraying traditionally used to produce environmental barrier coatings (EBC). XRD analysis on as-sprayed coatings revealed amorphous or crystalline layers depending on plasma parameters. In EBC application, a volume change from crystallization or phase transformation was envisaged to be damaging due to induced stresses and fully crystalline phases are a key durability requirement for EBC from conventional plasma spraying. Yttrium disilicate is characterized by an important polymorphism whereas ytterbium disilicate does not show anyone. Thermal shock tests were carried out on as-sprayed and heat-treated coatings in order to assess the suitability of liquid plasma spraying to produce EBC. |