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| Abstract No.: |
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Scheduled at:
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Friday, June 09, 2017, Hall 27 2:20 PM
Plasma Spraying II
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| Title: |
Influence of porosity of 8YSZ thermal barrier coatings produced by atmospheric plasma spraying on CMAS and volcanic ash infiltration behavior
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| Authors: |
Marco Antonio Rivera-Gil* / Centro de Investigación y de Estudios Avanzados del Instituto Politecnico National, Mexico
Ravisankar Naraparaju / Deutsches Zentrum für Luft- und Raumfahrt, Germany
Uwe Schulz / Deutsches Zentrum für Luft- und Raumfahrt, Germany
Juan Muñoz Saldaña/ Centro de Investigación y de Estudios Avanzados del IPN, Mexico
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| Abstract: |
It is well known that the microstructure and particularly porosity of 8YSZ (7-8 wt.%Y2O3 stabilized ZrO2) thermal barrier coatings (TBC) plays a fundamental roll for their performance. It reduces the thermal conductivity and helps to withstand mechanical loads and strains caused by differences in the thermal expansion and by volume changes during heating-cooling cycles. Furthermore, the TBC-lifetime is reduced by the presence of calcium-magnesium aluminosilicates (CMAS) or volcanic ashes, which melt around the operation temperature of TBCs and fill open porosity, thereby penetrating through the whole TBC thickness. CMAS infiltration is driven by the amount, shape, and distribution of pores within these TBCs. Hence, the degree of porosity of the 8YSZ coating must be controlled. This work addresses the effect of porosity variation in the range between 5 11 % porosity on CMAS infiltration resistance of 8YSZ coatings produced by atmospheric plasma spraying. The effect of spray distance, plasma current and powder feed rate on in-flight particle characteristics (temperature and velocity) as well as on microstructure (thickness, porosity) of coatings on heated Al2O3 substrates was investigated. Aluminum oxide is used as substrate material in order to reach a better understanding of CMAS-8YSZ chemical interaction and to allow controlled infiltration experiments at very high temperatures. The infiltration behavior by CMAS and volcanic ash and their influence on TBC performance was studied through isothermal infiltration experiments. 8YSZ coatings with more than 90% tetragonal phase were successfully deposited. As expected, the porosity level was mostly influenced by the stand-off distance and the powder feed rate during the APS deposition as observed from the 3D surface plots showing the potential relationship between the APS deposition parameters. A substantial influence of the porosity of the APS TBC on the infiltration behavior was found, which clearly demonstrates the importance of microstructure tailoring in TBCs.
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