Degradation of Thermal Barrier Coatings by Fuel Impurities and CMAS: Thermochemical Interactions and Mitigation Approach
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JTTEE5 19:156–167 DOI: 10.1007/s11666-009-9424-0 1059-9630/$19.00 ASM International
Degradation of Thermal Barrier Coatings by Fuel Impurities and CMAS: Thermochemical Interactions and Mitigation Approaches Prabhakar Mohan, Travis Patterson, Bo Yao, and Yongho Sohn (Submitted July 20, 2009; in revised form September 1, 2009) Degradation of free-standing yttria-stabilized zirconia (YSZ) and CoNiCrAlY coatings (300 lm) due to V2O5 and a laboratory-synthesized CMAS was investigated at temperatures up to 1400 °C. Reactions, phase transformations, and microstructural development in coatings were examined by using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The molten deposits destabilized the YSZ and reacted with the thermally grown oxide with various phase transformations and reaction product formation. A dense, continuous environmental barrier overlay, based on oxides, applied by electrophoretic deposition was effective in mitigating the molten deposit attack. Enriching CMAS composition with Al promoted the crystallization of anorthite platelets and MgAl2O4 spinel, and mitigated CMAS ingression. EPD MgO overlay was also effective in protection against V2O5 melt by formation of magnesium vanadates. EPD alumina overlay deposited on thermal barrier coatings with APS 8YSZ and bond-coated IN939 superalloy retained its adhesion and structural integrity after prolonged furnace thermal cycle test at 1100 °C.
Keywords
air plasma spray, barrier overlay coatings, CMAS sand, environmental degradation, thermal barrier coatings, vanadium pentoxide
1. Introduction Advanced gas turbine engines employ thermal barrier coatings (TBCs) to insulate hot-section metallic components. TBCs have become a critical technology for improving efficiency and performance of advanced gas turbines (Ref 1-4). TBCs are multilayered systems consisting of a ceramic topcoat, typically YSZ (ZrO2 stabilized with 7-8 wt.% Y2O3) for thermal insulation, a thermally grown oxide (TGO) scale, a metallic bond coat that also provides oxidation/corrosion resistance, and a superalloy substrate. The YSZ coatings are generally deposited either by air plasma spray (APS) or electron This article is an invited paper selected from presentations at the 2009 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Expanding Thermal Spray Performance to New Markets and Applications: Proceedings of the 2009 International Thermal Spray Conference, Las Vegas, Nevada, USA, May 4-7, 2009, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2009. Prabhakar Mohan, Travis Patterson, Bo Yao, and Yongho Sohn, Advanced Materials Processing and Analysis Center (AMPAC) and Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, FL 32816. Contact e-mail: [email protected].
156—Volume 19(1-2) January 2010
beam physical vapor deposi
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