SBIR Phase I: Designing an Immune System Response Into High-Temperature Ceramic Matrix Composite Materials (CMC)

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This Small Business Innovation Research Phase I project is designed to evaluate a novel interphase nanocoating designed for Silicon Carbide (SiC) fibers, which is intended to behave as a biomimetic immune system for high-temperature Ceramic Matrix Composites (CMCs) exposed to an oxidizing environment. High-temperature CMCs must survive oxidative and thermomechanical requirements that even the most advanced superalloys cannot withstand. Interphase coatings play a critical role in achieving these objectives. Interphase coatings represent a tiny fraction of the mass of a CMC, but are responsible for most of their outstanding properties. The coatings isolate fibers from the matrix and from each other, control failure mechanisms by regulating load transfer between fiber and matrix, and serve as an Environmental Barrier Coating (EBC) to protect the load-bearing fibers. In essence, an interphase coating is first and foremost a micromechanical system engineered for failure mitigation, oxidation prevention, and a slight self-healing. This Phase I effort aims to enhance these functions and add to them a material "immune response" capable of local detection of oxygen intrusion, followed by automatic compositional changes which resist further oxygen ingress, and finally the creation of "scar tissue" that leaves the area more resistant to future oxidation. The broader impact/commercial potential of this project will first be felt in terms of enhanced safety and reliability of high-temperature Ceramic Matrix Composite components used, for example, in jet engines, gas turbines, or nuclear power plants. The proposed nanocoating technology is made possible by a new fiber manufacturing platform technology, which allows a single process to accomplish what currently requires two separate, very expensive, processes. The cost of Silicon Carbide (SiC) fiber-reinforced CMCs can therefore be reduced while delivering drastically improved quality. Indeed, the proposed technology finally makes possible the introduction of affordable high-quality SiC fibers to our target markets. These markets include military and aerospace (turbo machinery, rockets, advanced structures), automobile, energy and other industries that require advanced materials with exceptional strength, stiffness, heat resistance, and/ or chemical resistance. SiC fibers alone, even without considering this coating, represent a fast-growing market with great potential, the collective size of which exceeds $2 billion. The technology enabling the proposed interphase coating has an energy footprint that is 1/1000th that of competing methods and which produces a fraction of the associated waste and emissions as well. This provides a huge cost advantage as well as a dramatic improvement in quality and performance.