Calcia-magnesia-alumino-silicate (CMAS)-induced degradation and failure of air plasma sprayed yttria-stabilized zirconia thermal barrier coatings

• Published in: Acta materialia Vol. 105; no. C; pp. 355 - 366
• Main Authors: Krause, Amanda R., Garces, Hector F., Dwivedi, Gopal, Ortiz, Angel L., Sampath, Sanjay, Padture, Nitin P.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 15.02.2016; Elsevier
• Subjects: CMAS; Degradation; Failure; Formations; Gas turbine engines; Glass; Mechanics; Thermal barrier coatings; Yttria stabilized zirconia; Zirconia; Zirconium dioxide; Zirconia; Thermal barrier coatings; Mechanics; CMAS; Glass
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2015.12.044

Thermal barrier coatings (TBCs) used in gas-turbine engines experience severe degradation by calcia-magnesia-alumino-silicate (CMAS) deposits during high-temperature operation. The present study identified and evaluated the chemical and microstructural changes in air plasma-sprayed (APS) 7 wt.% Y2O3 stabilized ZrO2 (7YSZ) TBCs caused by CMAS attack under isothermal conditions at 1340 °C. Additionally, a ‘model’ experimental study was conducted by characterizing 7YSZ ceramic powders immersed in molten CMAS glass at 1300 °C for different exposure times. The combined results from both studies highlight the importance of local CMAS glass composition on the 7YSZ/CMAS interaction. Specifically, low Y-content in the glass, caused by a relatively large glass 'sink,' produces Y-depleted ZrO2 grains that undergo tetragonal (t) → monoclinic (m) phase transformation upon cooling. Alternatively, small pockets of Y-enriched glass induce the formation of t″-ZrO2, a phase characterized by its high stabilizer content. After prolonged high-temperature exposure, solution-reprecipitation induces the formation of both m-ZrO2 and t″-ZrO2 throughout the APS 7YSZ TBC in accordance with the phase diagram. Using a thermomechanical model it is shown that the strain associated with the martensitic t→m phase transformation plays an important role in the delamination failure of TBCs attacked by CMAS. [Display omitted]