Title

Degradation Of Yttria Stabilized Zirconia Thermal Barrier Coatings By Molten Cmas (Cao-Mgo-Al2O3-Sio2) Deposits

Keywords

CMAS; Degradation; Thermal barrier coatings (TBC); YSZ (yttria stabilized Zirconia)

Abstract

In advanced gas turbine engines that operate in a dust-laden environment causing ingestion of siliceous debris into engines, thermal barrier coatings (TBCs) are highly susceptible to degradation by molten CMAS (calcium-magnesium alumino silicate) deposits. In this study, the degradation mechanisms other than the commonly reported thermomechanical damage are investigated with an emphasis on the thermochemical aspects of molten CMAS induced degradation of TBCs. Free-standing yttria stabilized zirconia (8YSZ) TBC specimens in contact with a model CMAS composition 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, the molten CMAS 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. Significant amount of Y2O3 depleted monoclinic ZrO2 phase evolved from CMAS melt that dissolved t'-ZrO2 was evident. Thus the mechanism of dissolution and reprecipitation due to molten CMAS damage resulted in destabilization of the YSZ with disruptive phase transformation (t' → f + m).

Publication Date

1-1-2008

Publication Title

Materials Science Forum

Volume

595-598 PART 1

Number of Pages

207-212

Document Type

Article; Proceedings Paper

Personal Identifier

scopus

Socpus ID

58149116406 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/58149116406

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