N101-036 TITLE: Impact/Erosion Resistant Environmental Barrier Coatings (EBCs) for Ceramic Matrix Composites (CMCs)

TECHNOLOGY AREAS: Air Platform, Materials/Processes

ACQUISITION PROGRAM: Joint Strike Fighter, Propulsion

OBJECTIVE: Develop and demonstrate innovative, impact/erosion resistant EBCs for Silicon Carbon (SiC) fiber-based CMCs.

DESCRIPTION: The JSF and other military platforms are targeting the use of CMCs for propulsion applications with a goal of increases in specific power. Concerns still exist regarding the degradation of CMCs at elevated temperature due to life limiting phenomena associated with thermal, chemical, and environmental instability of those material systems. EBCs or some other specifically purposed coatings in CMCs have been used at temperatures below 2,400 degrees Fahrenheit (1,316 degrees Celcius) in order to mitigate such deleterious environmental effects encountered in harsh engine operating conditions [1,2]. EBCs, however, have been shown to be highly susceptible to foreign object damage (FOD) [3] when subjected to particle impact or erosion by foreign objects ingested into hot sections of engines, as often observed in thermal barrier coatings (TBC) [4]. Impact/erosion, that exceeds certain limits, would result in spallation/delamination of EBCs, thus leading to premature failure of related CMC components. Furthermore, re-coating of EBCs is not economically feasible in many cases involving procedures that would be significantly cost-ineffective. It is, therefore, from a perspective of cost and performance, highly desirable to develop pertinent, prime-reliant EBCs that could withstand or alleviate impact/erosion damage at elevated temperatures to enhance overall durability and reliability of CMC components. The approaches should not degrade the important properties of EBCs such as thermal, chemical, and water-vapor stability with temperature capability below 2,400 degress Fahrenheit. Particular emphasis is in SiC fiber-based CMCs.

PHASE I: Develop innovative approaches to enhance impact/erosion resistance of EBCs in SiC fiber-based CMCs. Demonstrate the technical feasibility by fabricating and testing preliminary material systems.

PHASE II: Develop, demonstrate, and validate the pertinent EBC systems developed in Phase I. Evaluate the EBCs in terms of impact/erosion durability through appropriate tests using a reasonable number of test coupons.

PHASE III: Transition the approach to the Joint Strike Fighter (JSF) and other propulsion applications.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: CMC propulsion components have a great potential to transition to civilian aero engine applications. The resulting material development, albeit risky, could allow a significant life-cycle cost saving while the developed material could outperform the conventional coating systems.

REFERENCES:
1. Lee, K.N., Fox, D.S., Bansal, N.P.; "Rare Earth Silicate Environmental Barrier Coatings for SiC/SiC Composites and Si3N4 Ceramics", J. Eur. Ceram. Soc., 25 1705-1715 (2005)

2. Bhatia, T., Eaton, H., Sun, E., Lawton, T., Vedula, V.; "Advanced Environmental Coatings for SiC/SiC Composites", ASME Paper No. GT2005-68241 (2005), ASME Turbo Expo 2005

3. Bhatt, R.T., Choi, S.R., Cosgriff, L.M., Fox, D.S., Lee, K.N.; "Impact Resistance of Environmental Barrier Coated SiC/SiC Composites", Mater Sci. Eng., A 476 8-19 (2008)

4. Hazel, B., Fu, M., Schaedler, T., Darolia, R.; "Hard Particle Impact of Modulated TBC", presented at the 33rd International Conference & Exposition on Advanced Ceramics & Composites, January 18-23, 2009, Daytona Beach, FL; Paper No.ICACC-S2-012 5. Chen, X., Wang, R., Yao, N., Evans, A.G., Hutchinson, J.W., Bruce, R.W.; "Foreign Object Damage in Thermal Barrier System: Mechanism and Simulations," Mater. Sci. Eng., A 352 221-231 (2003)

KEYWORDS: Environmental Barrier Coatings (EBC); Ceramic Matrix Composites (CMC); Impact; Erosion; Foreign Object Damage (FOD); Silicon Carbon (SiC) Fiber-Reinforced CMCs

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