Accelerated oxidation during 1350°C cycling of ytterbium silicate environmental barrier coatings

Environmental barrier coatings (EBCs) will be needed to protect SiC-based ceramic matrix composite components for the next generation of high-efficiency industrial gas turbines (IGTs). The IGT application will require >= 25 kh lifetimes, and little data are available on EBC failure mechanisms, particularly at >= 1300 degrees C. Initial 1-h furnace cycle testing at 1350 degrees C in 90 vol% H2O/10 vol% air was conducted >= 1000 cycles on thermally sprayed ytterbium disilicate (YbDS) coatings with and without an Si bond coating. By >= 1000 h, both EBCs formed thick, highly cracked, and fully crystalline cristobalite scales. Comparison of thermally grown oxide (TGO) microstructure and kinetics to isothermal rates of Si and SiC steam oxidation indicated a departure from slow-growing parabolic growth to more rapid rates of silica formation. Possible mechanisms and implications for this acceleration are discussed.

Automated summary

Environmental barrier coatings (EBCs) are crucial for protecting SiC-based ceramic matrix composite components in next-generation high-efficiency industrial gas turbines (IGTs). However, limited data on EBC failure mechanisms exist, particularly at high temperatures. Experimental results showed that at elevated temperatures, EBCs formed thick, highly cracked, and fully crystalline cristobalite scales.