Thermal Shock Resistance of Yb2SiO5/Si and Yb2Si2O7/Si Coatings Deposited on C/SiC Composites

Rare-earth silicates, especially ytterbium silicate (Yb2SiO5and Yb2Si2O7), have been developed for promising environmental barrier coatings (EBCs) for SiC-matrix composites. In this study, double-layer Yb2SiO5/Si and Yb2Si2O7/Si EBC systems were deposited on C/SiC composites by air plasma spray (APS) technique, respectively. Both systems were subjected to thermal shock tests at 1400 °C. The evolution of phase composition and microstructure of those samples before and after thermal shock test were characterized. Results showed that there were penetrating microcracks in the top Yb2SiO5layer and horizontal microcracks at the Yb2SiO5-Si interface after thermal shock test. While extremely few microcracks and no horizontal microcracks were presented in the Yb2Si2O7/Si sample. The EDS analysis also showed that the Si bond layer of the Yb2SiO5/Si sample was oxidized more serious than that of the Yb2Si2O7/Si sample. The different thermal shock behaviors of both systems were clarified based on the thermal expansion behavior, phase composition and microstructure analysis.