Resistance of APS Y2O3 EBC against two artificial volcanic ash variants

Abstract

Ceramic matrix composites (CMC) are being developed for next generation aero-engines to substitute conventional superalloy components. However, the synergistic attack of increasing operation temperatures and water-rich exhaust gases demands for environmental barrier coatings (EBC) for protecting CMC components against thermochemical degradation. At DLR, a model CMC combustor liner with air-plasma-sprayed (APS) Y2O3 EBC has been demonstrated recently. Beyond heat and water-rich exhaust gases, ingestion and subsequent deposition of inorganic aerosols such volcanic ash (VA) is considered a major issue for EBC lifetime. In particular infiltration of open porosity by molten VA deposits is considered a major reason for “cold shock” fracture and subsequent EBC spallation. The behavior of APS Y2O3 EBC attacked by two test dusts similar to recent volcanic eruptions in Iceland, (Ejafjalla, 2010 and Grimsvotn, 2011), is presented in the light of phase formation, solid solubility, and microstructural evolution. APS Y2O3 EBC exhibit excellent resistance versus both VA-types at temperatures up to 1500°C at minimum. Melt infiltration is effectively mitigated by a low-permeable microstructure and rapid crystallization of Y-rich phases such as oxyapatites and silicates. Therfore, the thermochemical attack is occurring only close to the EBC surface.