High-temperature interaction of yttria stabilized zirconia coatings with CaO–MgO–Al2O3–SiO2 (CMAS) deposits

Yttria stabilized zirconia (YSZ) thermal barrier coatings (TBC) can be destabilized by combustions products, formed due to either dirty fuel or dust ingested through the air intake. The origin of this destabilization is high-temperature interaction of YSZ with molten calcium-magnesium-alumino-silicate (CMAS) deposits. The destabilization of the YSZ changes the behavior of the TBC, finally leading to failure. As a part of this investigation, X-ray powder diffraction, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) studies of ex-service combustor tiles subjected to CMAS attack have been performed. Rietveld refinement of powder diffraction patterns is allowed for the quantitative analysis of phase transformations, chemical composition change of YSZ and reconstruction of the scheme of element migration during the interaction of YSZ with the CMAS deposit. The composition of the deposit that infiltrated the open pores of the YSZ was found to be different from the average deposit composition. Based on the results, some solutions to protect YSZ against CMAS attack are discussed.