Silicon Carbide/Boron Nitride Dual In-Line Coating of Silicon Carbide Fiber Tows

This SBIR Phase I project will demonstrate monolayer and dual layer coating of SiC fiber by leveraging Laser Chemical Vapor Deposition techniques developed by Free Form Fibers for direct fiber production. Ceramic fibers, particularly SiC, must be coated in order to protect the fibers from oxidizing environments, and to allow their use in SiC CMC's. FFF's LCVD techniques can be modified for fast, high purity coating. The Phase I effort includes creating a custom reactor that leverages FFF's existing gas precursor delivery infrastructure, and passing existing monofilament SiC fiber through the reactor to coat with BN in real time. Reversing direction and coating the coated fiber with SiC will be done for dual layer coating. Phase II would scale the process to serially dualcoat a unidirectional moving parallel array of hundreds or thousands of moving fibers. If successful, industry would finally have a reliable in-line approach to fiber coating prior to tow production, because spreading and coating already-sized tows is nearly impossible. Based on prior coating experience and other related proposals, Phase I work would take us from TRL3 to TRL4. Phase II could take us to TRL4 or TRL5, either on a FFF or other commercial fiber production facility.

In-situ coating of disparate fibers affects a wide variety of composites applications. In the case of SiC fiber with dual Boron Nitride/Silicon Carbide coatings, the most important applications include commercial jet engines and turbo-machinery-based power generation equipment. Both require higher operating temperatures in order to reach ever higher fuel efficiencies, and the consensus is that SiC/SiC ceramic matrix composites are the path to that future; the BN/SiC coating system is a highly desired element of this particular CMC. Other non-NASA applications of the proposed generic fiber coating process may well include advanced structural composites, where new high performance fibers are used in next-gen materials systems. The process may also have value in CMC tooling applications, where fracture toughness and wear resistance are achieved through a tungsten carbide composite, for example. The ability to apply fiber coatings during, or just after fiber production, improves the cost/benefit ratio for composites production.

Over the last quarter century NASA and DoD have demanded high temperature materials capable of operating in oxidizing environments. Government and industry alike have invested large amounts in SiC-based technology for this purpose. Yet, for all that has been invested, fiber purity and protection still remains insufficient to address the needs of 2700 F and above applications. Beyond this temperature, not only are there benefits reaped from higher efficiency engines, but the weight penalty of cooling equipment is lifted. NASA's most immediate benefit from this proposed and other related research relates to advanced propulsion and power generation, for example the Ultra-Efficient Engine Technology Program. In addition, as composites become more ubiquitous in ever more demanding NASA applications such as high performance structures, the demand for coated fibers is likely to increase. A generic, material-agnostic platform for fast fiber coating is of considerable value to future NASA composite development efforts.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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