High-temperature interactions between Yttria-stabilized zirconia thermal barrier coatings and Na-Rich calcia-magnesia-aluminosilicate deposits

Abstract

We have evaluated the effectiveness of optical basicity, a chemical model, to predict and categorize the reaction behavior between calcia-magnesia-aluminosilicate (CMAS) deposits and ZrO2-based thermal barrier coatings (TBCs), which are used to insulate and protect metallic components in gas-turbine engines. The attack behavior of two CMAS compositions (Na-lean and Na-rich) with 7 wt% Y2O3-partially-stabilized ZrO2 (7YSZ) and 2ZrO2·Y2O3(ss) free-standing TBCs at 1340 °C were evaluated and compared to previous studies. The behavior of Y3+ in the reaction is correlated with the optical basicity of the CMAS; more basic Na-rich CMAS melt resulted in lower Y-solubility and higher Y-content in the reprecipitated ZrO2 grains than observed in the highly acidic CMAS attack for both tested TBCs. This behavior is consistent with previous studies of basic and acidic melts, and suggests that less acidic CMASs pose a unique danger to ZrO2-based TBCs that rely on Y-rich secondary phases for CMAS mitigation.