Microstructure evolution of CMAS glass below melting temperature and its potential influence on thermal barrier coatings

CaO–MgO–Al₂O₃–SiO₂ (CMAS) deposition significantly degrades the performance of thermal barrier coatings (TBCs). In this study, the microstructure evolution of CMAS glass at temperatures below its melting point was investigated in order to study the potential influence of temperature on the applicability of CMAS glass in TBCs. The CMAS glass fabricated in this study had a melting point of 1240 °C, became opaque, and underwent self-crystallization when the temperature reached 1000 °C. After heat treatment at 1050 °C, diopside and anorthite phases precipitated from the glass; at a higher temperature (1150 °C), diopside, anorthite, and wollastonite were formed as the self-crystallization products. An increase in the dwelling time resulted in the transformation of diopside to wollastonite and anorthite. At 1250 °C, all products formed a eutectic microstructure and melted. The results indicate that even at low temperatures, CMAS glass underwent microstructure evolution, which could influence the coating surface and stress distribution when deposited on TBCs.