N141-074 TITLE: Robust Matrices for 27000F Ceramic Matrix Composites

TECHNOLOGY AREAS: Air Platform, Materials/Processes

OBJECTIVE: Develop mature physics and thermo-chemical-based foundation needed to underlay the development of advanced matrices with improved environmental robustness that can mitigate the effects of coating loss (viz. CMC exposure to moisture-induced volatilization or corrosive deposits), or matrix cracking (leading to oxidative embrittlement of the CMC) in high temperature gas turbine hot section components.

DESCRIPTION: Implementation of SiC-based ceramic matrix composites (CMCs), in propulsion engines of interest to the US Navy, is now a tangible reality, representing the most fundamental change in design and manufacturing practices for gas turbines since the introduction of single crystal super-alloys. However, application of SiC-based CMCs in combustion environments requires the use of protective environmental barrier coatings (EBCs) to prevent volatilization of the protective silica scale from water vapor present in propulsion gases, as well as attack from ingested ash, sand etc. (calcium-magnesium-alumino-silicate (CMAS) attack). The EBC only provides protection while present on the surface. Cracking and spallation of the coating leaves the underlying SiC vulnerable to oxidation/volatilization as well as other forms of damage. There is need for robust matrices, chemically tailored to re-grow protective scales and to heal cracks extending into the CMC itself. To date, CMC matrices and EBCs have been developed heuristically. While both the thermo-mechanical performance of CMCs and the thermo-chemical behavior of EBCs have been addressed, the latter arguably to a lesser degree, an integrated, science-based perspective that can underpin the development of such systems approach has yet to emerge. The Integrated Computational Materials Engineering (ICME) strategy must include modeling approaches that can describe the relevant thermo-mechanical and thermo-chemical behavior of ceramic matrices, as well as the overall system and its constituents, combined with experimental approaches to generate requisite information for model validation. The capability to design and manufacture robust, self-healing matrices would be invaluable for extending the durability of critical gas turbine engine hot section components. This will lead to improved life management of these high value components and a concomitant reduction in their sustainment costs.

PHASE I: Using ICME functionalities, establish models to predict the effect of composition on phase stability and key properties in ceramic matrices such as thermomechanical and thermochemical behavior, as well as thermodynamics and kinetic to predict system evolution due to inter-diffusion between constituents, phase transformations or interactions with the environment. The models should lead to application of self-healing environmental barrier coatings that can withstand the rigors of aggressive environments (such as 2400 deg F). The ICME effort needs to be combined with experimental approaches to generate requisite information for model validation.

PHASE II: Apply validated models, developed in Phase I, to the synthesis of advanced matrices and coatings, initially as monolithic materials and later in sub-systems and complete EBC/CMC systems. In coordination with an appropriate original equipment manufacturer, establish and execute a test plan that will provide sufficient data for preliminary assessment of design allowables for critical and relevant design requirements.

PHASE III: Adoption of models/optimized matrix by an original equipment manufacturer (OEM) for further maturation to manufacture robust self-healing matrix CMC components that can operate in complex environments with less maintenance, lower overall life cycle cost, and improved operational capabilities. The small business and the engine OEM would work towards further maturation of the knowledge and/or process to fabricate CMC engine components for military and commercial platforms.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: There is increasing need for commercial airlines to reduce fuel consumption for better profitability and reduced emissions, as well as establish technology that will allow the design and manufacture of more robust commercial engines.

REFERENCES:
1. G. Evans, F. W. Zok, R. M. McMeeking, and Z. Z. Du, "Models of high temperature, environmentally assisted embrittlement in ceramic-matrix composites," J. American Ceramic Society, 79 (1996) 2345-2352.

2. F.S. Lauten and M.T. Schulberg, "Composite Materials for Leading Edges of Enhanced Common Aero Vehicles and Hypersonic Cruise Vehicles", Physical Sciences Inc., 2006.

KEYWORDS: Ceramic matrix composites, environmental barrier coatings, oxidation, thermo-chemical model, mechanical property model, gas turbine engine

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