Interfacial characteristics and adhesion behaviour of ytterbium silicate environmental barrier coatings exposed to steam oxidation

Regardless of the processing technique and resulting microstructure, when Environmental Barrier Coatings (EBCs) are exposed to high temperature in an air or steam environments, oxidation of the silicon bond coat forms a Thermally Grown Oxide (TGO). This study investigates the effect of steam oxidation on failure of air plasma sprayed (APS) EBCs consisting of a Yb2Si2O7 based topcoat and silicon bond coat, primarily focusing on changes at the topcoat and bond coat interface such as TGO thickness, interface roughness, pore size and pore morphology. Furthermore, it also explores the interfacial bonding behaviour at different length scales with scratch testing and in-situ cantilever beam bending. The findings reveal that the topcoat's microstructure, including the crack network and grain size, influence the inhomogeneity in TGO thickness, while interfacial pore formation and non-uniform stress distribution weaken the TGO/topcoat interface.