High temperature oxidation of magnetron sputtered Y2O3 doped silicon bond coats for SiC/SiC CMCs

Silicon carbide (SiC) ceramic matrix composites (CMCs) are increasingly used in the high-temperature sections of turbine engines, requiring robust environmental barrier coating (EBC) systems to withstand extreme conditions. A silicon-based bond coat typically serves as the interface between the CMC and the EBC, although limitations remain for its long-term oxidation resistance and mechanical stability. In this study, yttria (Y 2 O 3 ) doped silicon bond coats deposited by magnetron sputtering on monolithic SiC were investigated to improve these properties. Two compositions, 13 mol% and 25 mol% of YO 1.5 in silicon, were synthesized, yielding X-ray amorphous, homogeneous, and columnar structures. Furnace cycling tests were performed up to 1000 cycles at 1250 °C to evaluate the high temperature oxidation behavior of the coatings. Microstructural evolution and phase transformations were analyzed using scanning electron microscopy (SEM), focused ion beam (FIB), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Upon thermal exposure, the films crystallized and during oxidation they form a thermally grown oxide (TGO) layer. The low-doped Y₂O₃ bond coat exhibited improved oxidation resistance, while the high-doped Y₂O₃ bond coat exhibited rapid pathways for oxygen due to the formation of yttrium disilicate (Y₂Si₂O₇), which induced pores and promoted inhomogeneous distribution of the Y₂O₃ phases. The study concludes that optimized Y 2 O 3 doping can enhance oxidation resistance in Si based bond coat for CMC applications, with low Y 2 O 3 content showing superior performance.