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Chemical and Mechanical Consequences of Environmental Barrier Coating Exposure to Calcium-Magnesium-Aluminosilicate

Harder, Bryan J. and Ramírez-Rico, Joaquin and Almer, Jonathan D. and Lee, Kang N. and Faber, Katherine T. (2011) Chemical and Mechanical Consequences of Environmental Barrier Coating Exposure to Calcium-Magnesium-Aluminosilicate. Journal of the American Ceramic Society, 94 (S1). S178-S185. ISSN 0002-7820.

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The success of Si-based ceramics as high-temperature structural materials for gas turbine applications relies on the use of environmental barrier coatings (EBCs) with low silica activity, such as Ba_(1−x)Sr_xAl_2Si_2O_8 (BSAS), which protect the underlying components from oxidation and corrosion in combustion environments containing water vapor. One of the current challenges concerning EBC lifetime is the effect of sandy deposits of calcium–magnesium–aluminosilicate (CMAS) glass that melt during engine operation and react with the EBC, changing both its composition and stress state. In this work, we study the effect of CMAS exposure at 1300°C on the residual stress state and composition in BSAS–mullite–Si–SiC multilayers. Residual stresses were measured in BSAS multilayers exposed to CMAS for different times using high-energy X-ray diffraction. Their microstructure was studied using a combination of scanning electron microscopy and transmission electron microscopy techniques. Our results show that CMAS dissolves the BSAS topcoat preferentially through the grain boundaries, dislodging the grains and changing the residual stress state in the topcoat to a nonuniform and increasingly compressive stress state with increasing exposure time. The presence of CMAS accelerates the hexacelsian-to-celsian phase transformation kinetics in BSAS, which reacts with the glass by a solution–reprecipitation mechanism. Precipitates have crystallographic structures consistent with Ca-doped celsian and Ba-doped anorthite.

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Additional Information:© 2011 The American Ceramic Society. Manuscript No. 28705. Received September 30, 2010; approved January 14, 2011. This work was supported by the Department of Energy, Office of Basic Energy Science, under contract number DE-AC02-06CH11357. Microscopy images were collected at the NUANCE Center at Northwestern University, which is supported by the MRSEC program of the National Science Foundation (DMR-0520513). J. Ramirez-Rico was partially funded by the Spanish Ministry of Science and Technology under grant MAT2007-30141-E.
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-06CH11357
Spanish Ministry of Science and Technology MAT2007-30141-E
Issue or Number:S1
Record Number:CaltechAUTHORS:20140908-181320055
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Official Citation:Harder, B. J., Ramìrez-Rico, J., Almer, J. D., Lee, K. N. and Faber, K. T. (2011), Chemical and Mechanical Consequences of Environmental Barrier Coating Exposure to Calcium–Magnesium–Aluminosilicate. Journal of the American Ceramic Society, 94: s178–s185. doi: 10.1111/j.1551-2916.2011.04448.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49370
Deposited By: George Porter
Deposited On:09 Sep 2014 15:53
Last Modified:03 Oct 2019 07:13

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