TGO Growth Behavior in Environmental Barrier Coatings with Modified Silicon Bond Coat

Yb2Si2O7/Si bilayer environmental barrier coatings (EBCs) are widely studied for the protection of SiC-based ceramic matrix composites (CMCs). One life-limiting factor for EBCs exposed to high-temperature steam environments is the formation and growth of cracked thermally grown oxide (TGO), which is caused by the volume contraction during beta-cristobalite to alpha-cristobalite phase transformation upon cooling to similar to 220 degrees C. The cracked TGO provides a short diffusion path for oxidants and results in accelerated TGO growth and a short EBC life. Therefore, EBCs need a new bond coat that can prevent the thermally grown SiO2 from cracking as well as the resultant fast growth. In this study, a Si bond coat modified with Al2O3 was developed, and the oxidation behavior of EBCs using the modified Si bond coat was evaluated in flowing 90% H2O (g) + 10% air at 1316 degrees C. It was observed that no TGO cracking occurred when a certain amount of Al3+ and Yb3+ were dissolved in the TGO. The TGO growth rate in the EBCs with modified Si bond coat was similar to 28% slower than that of baseline EBCs with Si bond coat.