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Residual stress and microstructural evolution in tantalum oxide coatings on silicon nitride

Weyant, C. M. and Faber, K. T. and Almer, J. D. and Guiheen, J. V. (2005) Residual stress and microstructural evolution in tantalum oxide coatings on silicon nitride. Journal of the American Ceramic Society, 88 (8). pp. 2169-2176. ISSN 0002-7820. doi:10.1111/j.1551-2916.2005.00396.x.

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Due to its coefficient of thermal expansion (CTE) and phase stability up to 1360°C, tantalum oxide (Ta_2O_5) was identified and investigated as a candidate environmental barrier coating for silicon nitride-based ceramics. Ta_2O_5 coatings were plasma sprayed onto AS800, a silicon nitride ceramic from Honeywell International, and subjected to static and cyclic heat treatments up to 1200°C in air. Cross-sections from coated and uncoated substrates were polished and etched to reveal the effect of heat treatments on microstructure and grain size. As-sprayed coatings contained vertical cracks that healed after thermal exposure. Significant grain growth that was observed in the coatings led to microcracking due to the anisotropic CTE of Ta_2O_5. High-energy X-ray diffraction was used to determine the effect of heat treatment on residual stress and phases. The uncoated substrates were found to have a surface compressive layer before and after thermal cycling. Coating stresses in the as-sprayed state were found to be tensile, but became compressive after heat treatment. The microcracking and buckling that occurred in the heat-treated coatings led to stress relaxation after long heat treatments, but ultimately would be detrimental to the function of the coating as an environmental barrier by affording open pathways for volatile species to reach the underlying ceramic.

Item Type:Article
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Faber, K. T.0000-0001-6585-2536
Additional Information:© 2005 The American Ceramic Society. Manuscript No. 20199. Received October 21, 2004; approved February 22, 2005. This material is based upon work supported by U.S. Department of Energy Cooperative Agreement No. DE-FC02-01CH11086 awarded to Northwestern University. Any opinions, finding, conclusions, or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the United States Department of Energy or Northwestern University. Use of the APS was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Science, under contract number W-31-109-Eng-38. The authors would like to thank H. Chan of Lehigh University, who provided bulk Ta_2O_5 samples.
Funding AgencyGrant Number
Department of Energy (DOE)DE-FC02-01CH11086
Department of Energy (DOE)W-31-109-ENG-38
Issue or Number:8
Record Number:CaltechAUTHORS:20140908-181320843
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Official Citation:Weyant, C. M., Faber, K. T., Almer, J. D. and Guiheen, J. V. (2005), Residual Stress and Microstructural Evolution in Tantalum Oxide Coatings on Silicon Nitride. Journal of the American Ceramic Society, 88: 2169–2176. doi: 10.1111/j.1551-2916.2005.00396.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:49377
Deposited By: George Porter
Deposited On:09 Sep 2014 15:03
Last Modified:10 Nov 2021 18:43

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