2ZrO2·Y2O3 Thermal Barrier Coatings Resistant to Degradation by Molten CMAS: Part II, Interactions with Sand and Fly Ash

Abstract

Based on the application of OB considerations (Part I) to various major thermal barrier coating (TBC) compositions and two types of important calcium–magnesium–alumino–silicates (CMAS)—desert sand and fly ash—the 2ZrO2·Y2O3 solid solution (ss) TBC composition, with high CMAS‐resistance potential, is chosen for studying molten‐CMAS/TBC interactions. It is demonstrated that 2ZrO2·Y2O3(ss) air plasma sprayed (APS) TBCs are highly resistant to high‐temperature attack by both sand‐CMAS and fly‐ash‐CMAS. Despite the differences in the compositions of the two CMASs, the overall CMAS‐attack mitigation mechanisms in both cases appear to be similar, viz reaction between 2ZrO2·Y2O3(ss) APS TBC and the CMAS, and the formation of main reaction products of Y‐depleted c‐ZrO2 and nonstoichiometric Ca–Y apatite. Large differences in the OBs (ΔΛ) between the 2ZrO2·Y2O3(ss) and the CMASs are good predictors of ready reaction between this TBC and these CMASs. While the details of the CMAS‐mitigation mechanisms can depend critically on various other aspects, the OB difference (ΔΛ) calculations could be used for the initial screening of CMAS‐resistant TBC compositions.