Grain boundary corrosion mechanism of YSZ thermal barrier oxides under CMAS attack

Grain boundary (GB) corrosion of yttria-stabilized zirconia (YSZ) under calcium-magnesium-alumino-silicates (CMAS) attack was investigated. Dense YSZ ceramics with YO1.5 contents varying from 8 to 57 mol.% were prepared, and exposed to CMAS at 1300 degrees C. The results show preferential GB corrosion occurs for all YSZ ce-ramics, and the extent of corrosion significantly depends on the YO1.5 concentration. For low YO1.5 YSZ (e.g. 8YSZ and 20YSZ), GB is rapidly dissolved and infiltrated by CMAS melt. In contrast, for YSZ with high YO1.5 contents (e.g. Y2Zr2O7 and Y4Zr3O12), a uniform corrosion through the GB and grains is observed. The reason of the preferential GB corrosion is attributed to segregation of Y element in YSZ, which promotes the CMAS reactivity with the GBs. Furthermore, the mechanism of extent difference of GB corrosion in YSZ materials is discussed. It is proposed that the GB corrosion of YSZ can be mitigated by decreasing the Y segregation, increasing the relative volume of reaction products, and/or promoting the precipitation kinetic of products.