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2077 |
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Mechanical behavior of air plasma sprayed functionally graded YSZ-mullite environmental barrier coatings: a study via instrumented indentation |
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Cristian Victor Cojocaru / National Research Council Canada / Industrial Materials Institute, Canada Youliang Wang / National Research Council of Canada, Industrial Materials Institute, Canada Christian Moreau/ National Research Council of Canada, Industrial Materials Institute, Canada Rogerio Soares Lima/ National Research Council of Canada, Industrial Materials Institute, Canada Joana Mesquita-Guimarães/ Institute of Ceramics and Glass (CSIC), Spain Eugenio Garcia/ Institute of Ceramics and Glass (CSIC), Spain Pillar Miranzo/ Institute of Ceramics and Glass (CSIC), Spain Maria Isabel Osendi/ Institute of Ceramics and Glass (CSIC), Spain |
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Mullite (Al6Si2O13) is the basis of efficient environmental barrier coatings (EBCs) for protecting Si-based ceramic matrix composites (CMCs) selected to replace specific hot-section metallic components in advanced gas turbines. Furthermore, YSZ-mullite multilayer architectures with compositional grading between the bond coat and top YSZ coat were envisioned as solutions to ease their coefficient of thermal expansion (CTE) mismatch induced stress. Consequently a proper understanding of the mechanical properties such as the elastic modulus, hardness or plastic/elastic recovery work serve for an efficient design of such refractory oxide multilayers. In this work, three different mullite powder morphologies (fused and crushed, spray-dried and freeze-granulated) were employed. Using depth-sensing indentation with loads in the range 100 ? 500 mN, the role of the microstructure and morphology of the powder feedstock on the mechanical behaviour of air plasma sprayed mullite bond coats deposited on SiC Hexaloy substrates was investigated. Fully crystalline as-sprayed mullite coatings were engineered under controlled deposition conditions. Mechanical properties were measured for the as-sprayed coatings as well as for coatings heat-treated at 1300oC, in water vapours environment, for periods up to 500 h. Comparable values for the elastic modulus and hardness of the mullite coatings obtained with fused and crushed with the other powders were correlated with their crack-free microstructure. |