2ZrO 2 ·Y 2 O 3 Thermal Barrier Coatings Resistant to Degradation by Molten CMAS : Part II , Interactions with Sand and Fly Ash

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 2 ZrO 2 · Y 2 O 3 solid solution (ss) TBC composition, with high CMAS ‐resistance potential, is chosen for studying molten‐ CMAS / TBC interactions. It is demonstrated that 2ZrO 2 ·Y 2 O 3 (ss) air plasma sprayed ( APS ) TBC s are highly resistant to high‐temperature attack by both sand‐ CMAS and fly‐ash‐ CMAS . Despite the differences in the compositions of the two CMAS s, the overall CMAS ‐attack mitigation mechanisms in both cases appear to be similar, viz reaction between 2ZrO 2 ·Y 2 O 3 (ss) APS TBC and the CMAS , and the formation of main reaction products of Y‐depleted c ‐ ZrO 2 and nonstoichiometric Ca – Y apatite. Large differences in the OB s (ΔΛ) between the 2ZrO 2 ·Y 2 O 3 (ss) and the CMAS s are good predictors of ready reaction between this TBC and these CMAS s. 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.