Thermochemical interaction of (Yb_0.7Gd_0.3)₄Hf₃O₁₂ ceramic with CMAS melts

The molten calcium-magnesium alumino-silicate (CMAS) deposits degradation of thermal barrier coatings (TBCs) is increasingly severe in advanced turbine engines. In this study, the thermochemical interaction of a promising TBC candidate material, (Yb_0.7Gd_0.3)₄Hf₃O₁₂, with CMAS melts at 1300 ℃ and 1500 ℃ was systematically investigated. The apatite and reprecipitated fluorite with high melting points were crystallized rapidly when the ceramic reacted with CMAS melts, resulting in the formation of a dense crystalline layer to suppress further infiltration of CMAS melts. Moreover, as the reaction proceeded, the formation of garnet and cuspidine occurred at 1300 ℃ and 1500 ℃, respectively. The CMAS resistance of (Yb_0.7Gd_0.3)₄Hf₃O₁₂ was significantly higher compared to that of Yb₄Hf₃O₁₂, which could be attributed to the greater volume fraction of apatite and reprecipitated fluorite in the reaction products. The (Yb_0.7Gd_0.3)₄Hf₃O₁₂ exhibited high effectiveness in mitigating CMAS infiltration, making it a potential candidate material for thermal barrier coatings.