Environmental Barrier Coating Systems for SiC/SiC CMCs with Enhanced High Temperature Capability - EBCeTeC

• Applicants: Professor Dr.-Ing. Dietmar Koch; Professor Dr. Robert Vaßen, since 8/2024
• Subject Area: Glass, Ceramics and Derived Composites
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 532752369

SiC fiber-reinforced SiC matrix ceramic matrix composites (CMC) are advanced structural materials for hot sections of gas turbine engines. They are already in-service commercially, both for aircraft propulsion and electricity generation. In comparison to their Ni-based counterparts, SiC offers very high-temperature capability, low density, good mechanical properties at high temperature as well as oxidation resistance in air. In a water vapor-rich combustion atmosphere however, SiC is susceptible to rapid oxidation and subsequently to recession via volatilization of the formed SiO2 scale. For that reason, Environmental Barrier Coatings (EBCs) are used to shield SiC/SiC CMCs from the combustion atmosphere. The state of the EBC is a two-layer system consisting of a Si bond coat and Yb-disilicate (Yb2Si2O7) topcoat. Si bond coat protects the CMC from oxidation by forming a SiO2 scale while the topcoat serves as a volatilization barrier. The maximum temperature limit of this EBC system is ~1350°C. EBCs have been developed since mid of the 1990s yet no alternative system with higher temperature capability could have been established. Furthermore, although the EBCs are developed for protecting CMCs, degradation mechanisms of EBCs were only reported on sintered SiC substrates thus far in the literature by omitting the complex CMC-coating interface. In this project, a new and higher temperature resistant composite bond coat consisting of a rare earth aluminosilicate and SiC particles will be developed where SiC particles will act as oxygen getters within the glass-ceramic matrix. To that end, SiC/SiC CMCs will be manufactured by polymer infiltration and pyrolysis (PIP) and reactive melt infiltration (RMI) processes. After surface adaption of the CMCs the coating will be applied by a deposition method known from SiC joining technology. Rare earth aluminosilicate glass particles and SiC particles will be mixed with alcohol to obtain a slurry and then will be applied to CMC surfaces. Subsequently, the coated CMCs will be heated to the melting temperature of the glass under a protective atmosphere and the coating will be crystallized. The goal is to achieve a bond coat system that prevents effectively the oxidant diffusion, which has a coefficient of thermal expansion close to that of SiC/SiC, and which shows a comparably good bonding to the established Si bond coat. After the bond coat layer is realized, a Yb-silicate topcoat layer will be applied using the atmospheric plasma spraying technique. The cyclic oxidation and steam corrosion resistance of the newly developed layers will be investigated using furnace and burner rig testing up to 1500 °C. Through these tests, material interactions, structural changes, and degradation mechanisms of EBCs will be identified and evaluated under engine-like operation conditions. The knowledge gained from this project will be used to propose strategies for advanced coating systems for gas turbine engine components.

• DFG Programme: Research Grants
• Ehemalige Antragstellerin: Dr.-Ing. Emine Bakan, Ph.D., until 7/2024