Environmental Barrier Coatings for All-Oxide Ceramic Matrix Composite Gas Combustor Liners

Abstract

Gas turbine combustor liners made of all-oxide ceramic matrix composites (CMC) offer the potential of higher operation temperatures and increased efficiency compared to conventional superalloys with thermal barrier coatings. The harsh thermochemical environment of aero-engine combustors, however, impedes the application of state of the art Al2O3-based CMC, in particular at temperatures beyond 1200°C. The high water-vapor content of the combustion atmosphere can lead to volatilization and recession of Al2O3 whereas ingested inorganic aerosols such as desert dust or volcanic ash can trigger massive hot-corrosion. The latter mechanism is commonly referred to as CMAS degradation (CaO-MgO-Al2O3-SiO2) and is a major issue for aircraft operation in dust-laden environment such as middle-east airports. Environmental barrier coatings (EBC) are considered a key to the application of CMC. For long-term successful operation of EBC-protected CMC low thermal mismatch, good adherence, microstructural stability and resistance against water vapor recession and hot corrosion are mandatory material properties. Moreover, low thermal conductivity allows for additional thermal protection of CMC and thus increased lifetime of components.