2ZrO2·Y2O3Thermal Barrier Coatings Resistant to Degradation by MoltenCMAS: Part I, Optical Basicity Considerations and Processing

Abstract

The higher operating temperatures in gas‐turbine engines enabled by thermal barrier coatings (TBCs) engender new materials issues,vizsilicate particles (sand, volcanic ash, fly ash) ingested by the engine melt on the hotTBCsurfaces and form calcium–magnesium–alumino–silicate (CMAS) glass deposits. The moltenCMASglass degradesTBCs, 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 ofCMAS‐resistantTBCcompositions, which could also be extended to environmental barrier coatings (EBCs). By applyingOBdifference considerations to various majorTBCcompositions and two types of importantCMASs—desert sand and fly ash—the 2ZrO2·Y2O3solid solution (ss)TBCcomposition, with the potential for highCMAS‐resistance, is chosen for this study. Here, we also demonstrate the feasibility of processing of 2ZrO2·Y2O3(ss) air‐plasma sprayed (APS)TBCusing commercially developed powders. The resultingTBCs with typicalAPSmicrostructures are found to be single‐phase cubic fluorite, having a thermal conductivity <0.9 W·(m·K)−1at elevated temperatures. The accompanying PartIIpaper presents results from experiments and analyses of high‐temperature interactions between 2ZrO2·Y2O3(ss)APS TBCand the two types ofCMASs.