In-situ observation and directional growth of Ca2Lu8(SiO4)6O2 in Lu2SiO5 attacked by CMAS at 1500 °C

Excellent resistance to CMAS is one of the key parameters for environmental barrier coating (EBC) operated in gas turbine engines. The interaction between CMAS and EBC was usually investigated by the characterization of reaction products after corrosion. The lack of direct observation of the high-temperature CMAS corrosion processes hinders the understanding of CMAS-induced degradation of EBC. In this work, the interaction between CMAS and an EBC candidate (Lu2SiO5) was investigated by an in-situ observation method, where the melting of CMAS and the growth of reaction products were first observed. It was found that the reaction product Ca2Lu8(SiO4)6O2 tends to precipitate vertically to form a textured structure. In addition, Lu2SiO5 tends to decompose into Lu2Si2O7 and Lu2O3 at 1500 °C, which induces an intergranular infiltration of CMAS and leads to the formation of Ca2Lu8(SiO4)6O2 fringes. Compared with the corrosion behavior at 1300 °C, Lu2SiO5 exhibits fast interaction with CMAS and poor CMAS resistance at 1500 °C. The results provide important guidelines on the design of rare earth silicate EBC.