Low Cost Si-BN interface Coatings for SiC/SiNC CMCs.

MATECH GSM proposes to develop a low cost, uniform, reproducible Si-doped BN interface coating process for 3-D and 2-D woven ceramic fiber preforms. Using MATECH's new Reactive Transformation Process (RTP), Si-doped BN interface coatings will be demonstrated on woven SiC ceramic fiber performs without fiber-to-fiber bonding. Key parameters to be investigated will include: 1) Control of interface coating thickness, chemistry, and crystallinity, 2) Uniformity of interface coating thickness and composition, 3) Batch-to-batch reproducibility, 4) Retention of as-received ceramic fiber strength, and 5) Mechanical properties of fully densified SiNC-CMC coupons with RTP-derived Si-doped BN interface coatings. The current "state-of-the-art" process for producing BN inter-phase is chemical vapor infiltration (CVI). One drawback of the CVI BN process is that when a tow (500 to 800 fibers) is formed into a woven fiber preform prior to BN coating, many of the fibers are in contact with each other and therefore do not become completely coated. On subsequent fracture of the composite, those fibers that are in contact with no BN between them tend to fail in a brittle manner, little or no fiber pullout. The RTP coating mitigates these issues.