Title

Degradation Of Thermal Barrier Coatings By Fuel Impurities And Cmas

Abstract

Critical durability issues for thermal barrier coatings (TBCs) include their resistance against degradation by molten deposits arising from fuel impurities and air ingested CMAS (calciummagnesium alumino silicate) sand deposits. In this study, degradation of free-standing yttria stabilized zirconia (YSZ) and CoNiCrAlY coatings (300 μm) due to V2O5, P2O5, and a laboratory synthesized CMAS sand was investigated at temperatures up to 1400°C. Reactions, phase transformations and microstructural development in each coating were examined by using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. V2O5 melt was found to degrade the YSZ and CoNiCrAlY coatings through acidic dissolution of oxides resulting in preferential Y2O3 and ZrO2 depletion in YSZ, and a significant consumption of CoNiCrAlY through different reactions depending on reaction temperature. Similarly, P2O5 was found to degrade the coatings through acidic dissolution of coating constituents. CMAS melt degraded the YSZ coatings by ingression followed by gradual dissolution of YSZ that subsequently resulted in reprecipitation of ZrO2 grains with a structure and composition based on local melt chemistry. Density-functional theory calculations were also used to understand fundamental aspects of structure and reactions at the surface of fluorite-structured oxides. It was found that oxygen-vacancy clustering is critical for surface reactivity. An approach to mitigate such melt-induced attack is also introduced. An attempt to mitigate the melt-infiltration attack by dense, continuous environmental barrier overlay, applied by electropherotic deposition (EPD) is introduced. Copyright © 2009 ASM International® All rights reserved.

Publication Date

12-1-2009

Publication Title

Proceedings of the International Thermal Spray Conference

Number of Pages

89-96

Document Type

Article; Proceedings Paper

Personal Identifier

scopus

DOI Link

https://doi.org/10.1361/cp2009itsc0089

Socpus ID

76749137681 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/76749137681

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