2ZrO 2 ·Y 2 O 3 Thermal Barrier Coatings Resistant to Degradation by Molten CMAS : Part I, Optical Basicity Considerations and Processing

The higher operating temperatures in gas‐turbine engines enabled by thermal barrier coatings ( TBC s) engender new materials issues, viz silicate particles (sand, volcanic ash, fly ash) ingested by the engine melt on the hot TBC surfaces and form calcium–magnesium–alumino–silicate ( CMAS ) glass deposits. The molten CMAS glass degrades TBC s, leading to their premature failure. In this context, we have used the concept of optical basicity ( OB ) to provide a quantitative chemical basis for the screening of CMAS ‐resistant TBC compositions, which could also be extended to environmental barrier coatings ( EBC s). By applying OB difference considerations to various major TBC compositions and two types of important CMAS s—desert sand and fly ash—the 2 ZrO 2 · Y 2 O 3 solid solution (ss) TBC composition, with the potential for high CMAS ‐resistance, is chosen for this study. Here, we also demonstrate the feasibility of processing of 2ZrO 2 ·Y 2 O 3 (ss) air‐plasma sprayed ( APS ) TBC using commercially developed powders. The resulting TBC s with typical APS microstructures are found to be single‐phase cubic fluorite, having a thermal conductivity <0.9 W·(m·K) −1 at elevated temperatures. The accompanying Part II paper presents results from experiments and analyses of high‐temperature interactions between 2ZrO 2 ·Y 2 O 3 (ss) APS TBC and the two types of CMAS s.