Title

Degradation Of Thermal Barrier Coatings By Molten Cmas (Cao-Mgo-Al 2O3-Sio2) Deposits

Abstract

Thermal barrier coatings (TBCs) are susceptible to degradation by molten CMAS (calcium-magnesium alumino silicate) deposits, when employed in gas turbine engines operating in a dust-laden environment. In this study, thermochemical aspects of CMAS induced degradation of TBCs are thoroughly investigated. Free-standing yttria stabilized zirconia (8YSZ) coatings and CoNiCrAlY metallic coatings in contact with a model CMAS deposit were subjected to isothermal heat treatment in air at temperatures ranging from 1200°C to 1350°C. Phase transformations and microstructural development were examined by using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Starting at 1250°C, CMAS melt readily infiltrated and dissolved the YSZ coating followed by reprecipitation of zirconia with a different morphology and composition that depends on the local melt chemistry. The mechanism of dissolution and reprecipitation due to molten CMAS damage resulted in destabilization of the YSZ with disruptive phase transformation (t' → f + m). TGO scale of CoNiCrAlY coating was completely consumed by CMAS melt that was also accompanied by significant spinel oxide formation. Attempts to mitigate CMAS attack by employing an environmental barrier overlay composed of α-Al2O3 are also introduced. Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

Publication Date

1-1-2009

Publication Title

47th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition

Number of Pages

-

Document Type

Article; Proceedings Paper

Personal Identifier

scopus

DOI Link

https://doi.org/10.2514/6.2009-1433

Socpus ID

78549264102 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/78549264102

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