Melt-infiltration of 7 YSZ TBC on the example of two artificial volcanic ash variants

Abstract

The ingestion and subsequent deposition of volcanic ash (VA) is considered a major threat to performance and lifetime of aero-engines. Infiltration of ceramic thermal barrier coatings (TBCs) of combustor walls, turbine blades and vanes by molten VA deposits is associated with loss of strain tolerance, making them susceptible to “cold shock” fracture and subsequent spallation. An estimation of possible TBC damages by VA requires knowledge on dose, thermal history, and melt infiltration kinetics. Due to the high chemical and mineralogical variability of natural volcanic ashes, the selection of a test standard suitable for TBC infiltration experiments is still a major issue. Artificial volcanic ashes (AVA) providing tailored chemical composition and particle morphology are considered promising for standardized laboratory testing. The infiltration behavior of standard 7-YSZ TBC by two AVA test dusts similar to recent eruptions in Iceland, (Ejafjalla, 2010 and Grimsvotn, 2011), is discussed in the light of physical melt properties such as viscosity. It turns out that only small variations of the chemical composition may have major influence on melt infiltration onset and progress.