TBC corrosion by volcanic ash – properties and behavior of natural and artificial test dusts

The ingestion and subsequent deposition of volcanic ash (VA) is considered a major threat to performance and lifetime of aero-engines. Degradation of ceramic thermal barrier coatings (TBCs) of combustor walls, turbine blades and vanes is associated with chemical interaction between the TBC material and molten VA. Infiltration of molten VA also may affect the strain tolerance of TBCs, making them susceptible to “cold shock” fracture and subsequent spallation. Today there is still a major lack in the definition of standardized VA test dusts suited for ground testing and laboratory experiments. Chemical compositions and morphologies of natural volcanic ashes (NVA) are highly complex and variable. Artificial volcanic ash (AVA) is considered a promising alternative to NVA, providing tailored chemical composition and particle morphology. Key properties such as wetting and infiltration behavior of genuine volcanic ash (Ejafjalla, Iceland) and similar AVA test dusts are compared on the example of standard EB-PVD 7-YSZ TBC. Furthermore, a variety of properties of VA relevant to aero-engine operation are investigated