Thermal behavior and mechanical properties of Y₂SiO₅ environmental barrier coatings after isothermal heat treatment

Y₂SiO₅ coatings are deposited by a flame-spray technique as protection layer on SiC substrates to prevent oxidation and steam corrosion. In this research, Y₂SiO₅ coatings were isothermally heat treated at different temperatures and different exposure times in a laboratory environment. The thermal behaviors such as phase transformation, microstructural change and thermally grown oxide (TGO) formation have been examined by XRD, SEM, and EDS analysis. Different modes of TGO growth behavior were found at different temperatures. In addition, the mechanical properties were evaluated by a Martens hardness tester. The results show that the change of microstructure and composition is not too critical, but higher temperatures and longer heating times do lead to the formation of Y₂SiO₅ crystalline phases and a β-Y₂O₃ phase. Thus, the isothermal heat treatment improves the hardness and elastic modulus of Y₂SiO₅ coatings.