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.