Affordable Low Dielectric Ceramic Composites with Improved Interlaminar Strength

Hot structures fabricated from ceramic composite materials are an attractive design option for certain components of future aerospace vehicles and propulsion systems to reduce weight and increase survivability. Certain fabric-laminated ceramic composite components suffer from low interlaminar strength properties and are thus vulnerable to delamination when subjected to high thru-thickness thermal gradients and/or normal loads. This problem is of particular concern for pre-ceramic polymer-derived ceramic composite laminates that typically exhibit very low matrix dominated properties as compared to that produced by the chemical vapor infiltration (CVI) method. The objective of this proposed effort is to demonstrate the feasibility of producing an affordable fiber-reinforced ceramic-matrix composite material having low dielectric constant and significantly improved interlaminar properties. Low-cost 3D preforms using several commercially available low dielectric ceramic fiber types will be coated with a high-stability silicon-doped boron nitride (Si-BN) interphase and densified with high-strength/high-purity silicon nitride (Si3N4) produced by Hyper-Therm HTC's exclusive CVI process. Coupon specimens from the various composite systems produced will be evaluated to determine their respective in-plane and interlaminar mechanical properties, and electrical properties as a function of frequency. These results will be compared to a "baseline" fabric-laminated Si3N4 composite system to establish the overall viability of the proposed approach.