Novel Environmental Barrier Coatings for Ceramic Matrix Composites in Aero Engines

NASA has a significant interest in technologies that can increase the fuel efficiency and power density of gas turbines in aero engines, which dominates purchase decisions. The path for efficiency improvement is through increasing the turbine inlet temperature. Increased use of ceramic matrix composites (CMCs), specifically those based on silicon carbide (SiC), can increase inlet temperatures in excess of 2,700 F (1482 C) and reduce weight. However, SiC-based CMCs are susceptible to significant corrosion in water vapor present in combustion streams at such high temperatures. Therefore, gas turbine components made of these materials require an environmental barrier coating (EBC) to protect them from water vapor. The current state-of-the art EBCs have an operating temperature limit of about 1300 C, above which they themselves experience significant corrosion in water vapor. They are also significantly corroded by calcium magnesium aluminosilicates (CMAS) resulting from dust and volcanic debris. With NASA SBIR funding, a new EBC composition will be developed and demonstrated that is suitable for use at temperatures up to 1482oC. This composition will be selected from a new class of candidate EBC materials that have the potential for excellent matching of the thermal expansion coefficient to the SiC-based composites by altering the chemistry, resulting in improved durability. We will down-select the best candidate from a few thermal expansion matched compositions from this materials family that has sufficient water vapor corrosion resistance and chemical stability against CMAS at 1482 C. A coating of the down-selected composition will be made through a novel plasma spray process. The coating will then be tested in a highly realistic high velocity rig up to the target temperature of 1482 C, to demonstrate improved performance over state-of-the-art EBCs. This novel EBC technology is targeted at aero engines, as well as stationary gas turbines for utility-scale power.

NASA Aeronautics has a focused interest in next generation aero engines that can have increased fuel efficiency and power density relative to current technologies, and as such has an interest in the adoption of CMCs in aircraft. Thus, the development of new EBCs that can allow higher temperature operation of CMCs will help NASA achieve its long-term aeronautics goals, including the development of Advanced Propulsion systems for subsonic transport vehicles with high levels of thermal, transmission, and propulsive efficiency. The broader market is thermal energy, and the specific market segments are aircraft engines and natural gas turbines for stationary power generation. Thermal energy is the most dominant source of energy used around the world for both aircraft propulsion and electricity generation. Hence, it also has a greater installed capacity when compared with any other source of energy. EBC coating application services can be for blades, combustors, stator vanes, diffusers, and after-burner liners for new turbines or for component replacement or repair as part of maintenance, repair or overhaul (MRO) operations. Therefore, the demand for EBC coating services will scale with the demand for new aircraft engines and gas turbines and with the MRO market in both these segments (which in turn scales with cumulative installed capacity of these segments). If past history is any guide, new technology that can increase operating temperatures significantly such as the EBC-coated CMC engines/turbines will be adopted rapidly throughout the aircraft and power generation industries. There are a number of examples of new materials systems that have seen nearly universal adoption (single crystal nickel-based superalloys, thermal barrier coatings, etc). Thus, the total gas turbine market is a reasonable proxy for the served available market for EBC-coated CMCs.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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