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

Kurzfassung

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 (Y2O3) 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 YO1.5 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 Y2O3 doping can enhance oxidation resistance in Si based bond coat for CMC applications, with low Y2O3 content showing superior performance.