Chemical Degradation of the Ternary Al2O3–YAG–ZrO2 Eutectic Ceramic by Molten CMAS

Regarding potential high temperature applications of materials based on the ternary Al₂O₃-YAG-ZrO₂ (AYZ) eutectic system for turbine blades, their environmental behaviour has to be evaluated in near-service conditions. CMAS attack is one of the phenomena limiting lifetime of ceramic E/TBC coatings for aircraft engines. The present study reports an assessment of the reactivity of AYZ eutectic material facing with two molten CMAS. The effect of test duration (up to 500 h), CMAS composition (with or without Fe₂O₃), microstructure (interlamellar distance), temperature (1250 and 1350 °C) as well as thermal cycling resistance were investigated. Results evidenced that the interaction of CMAS with AYZ eutectic ceramic was limited regardless of the microstructure. No infiltration of molten CMAS within the eutectic ceramic nor mechanical rupture between CMAS and AYZ was observed. The dissolution of AYZ leads to the rapid formation of anorthite with the CMAS components that hinders further reactions. The inward growth of MgAl₂O₄ spinel in place of the Al₂O₃ network occurs in accordance with the thermodynamic available data and without any effect on AYZ integrity.