Finishing Process to Improve Interfacial Bonding in SiC/BMI Composites

High-temperature polymer matrix composites (PMCs) are desired for the aggressive environments encountered in many aerospace and military applications. These have required new blends of materials properties in the composite fiber and matrix. As polyimide resins have been improved, the thermo-oxidative stability (TOS) of the carbon fibers typically used as reinforcements have become a limiting factor for applications ranging from propulsion systems to structures for the orbiting space plane. Silicon carbide fibers provide a potentially attractive replacement for carbon fibers because of their higher thermal stability. Sizings for SiC fibers are not compatible with the new high-temperature matrix resins, which compromises composite properties. A need exists for a SiC fiber adhesion promoting finish that is compatible with high-temperature imide chemistries. Previous work has revealed chemistries that chemically bond to carbon fiber surfaces and high-temperature curing matrix resins. Composites fabricated with finishes based on these reactive coupling agent chemistries show substantially higher interface-dependent properties, TOS, and moisture resistance. The also function as weaving aids. Those chemistries will be modified to improve the interfacial bond between silicon carbide fibers and bismaleimide resins in the Phase I program. Results are expected to show that the modified reactive finishes allow control of interfacial adhesion in SiC/BMI composite systems that imparts superior interfacial strength and environmental durability.