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| Abstract No.: |
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Scheduled at:
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Wednesday, May 05, 2010, Sophia Room 10:40 AM
Aerospace Industry
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| Title: |
Mechanical properties and behavior of BSAS/mullite-based environmental barrier coatings exposed to high temperature in water vapor environment
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| Authors: |
Cristian Victor Cojocaru* / National Research Council Canada / Industrial Materials Institute, Canada
Christian Moreau / National Research Council Canada / Industrial Materials Institute, Canada
Rogerio Soares Lima/ National Research Council Canada / Industrial Materials Institute, Canada
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| Abstract: |
Si-based ceramics are known as promising high-temperature structural materials in various components where metals/alloys reached their ultimate performances (e.g., advanced gas turbine engines). To alleviate the thickness recess that Si-based ceramics undergo in a high-temperature environmental attack (e.g., H2O vapour) appropriate refractory oxides are engineered as environmental barrier coatings (EBCs). Presently, the state-of-the art EBCs comprise multilayers of mullite (Al6Si2O13) and BaO-SrO-Al2O3-SiO2 (BSAS). Evaluating and understanding their mechanical properties such as the elastic modulus, hardness and the strain-stress relationship is essential for their practical application and reliable employment. It was investigated via depth-sensing indentation and laser-ultrasonics the role of high-temperature treatment (1300 oC), performed in H2O vapour environment (for time intervals up to 500 h), on the mechanical behaviour of air plasma sprayed BSAS/mullite bilayers deposited on SiC Hexoloy substrates. The fully crystalline, crack-free or near crack-free as-sprayed EBCs were engineered under controlled deposition conditions. The stability of the low elastic modulus values (e.g., ~77 GPa) retained by the BSAS top layers even after harsh environmental exposures provides a plausible explanation for the almost crack-free coatings observed. The measured mechanical properties of the BSAS/mullite bilayers and their microstructural behaviour during the high-temperature exposure are discussed and correlated.
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