Manufacturing and characterization of polymer-derived ceramic matrix composites for high-temperature aerospace applications

Abstract

Ceramic matrix composites (CMCs) are engineered materials designed for operation in extreme environments, where their low density, high temperature capability, oxidation resistance, and damage tolerance make them attractive for aerospace and energy applications such as rocket nozzles, thermal protection systems, and turbine components. Polymer-derived ceramic matrix composites produced through polymer infiltration and pyrolysis (PIP) provide a relatively low-cost and scalable fabrication method compared to other ceramic composite manufacturing techniques. However, traditional PIP processing requires multiple infiltration and high-temperature pyrolysis cycles to build sufficient ceramic matrix content, resulting in long processing times and limited manufacturing scalability. This research investigates carbon fiber reinforced ceramic matrix composites produced using polysilazane and boron-modified polysilazane preceramic precursors to form SiCN and SiBCN ceramic matrices. Two processing methods were studied and compared. The first method used the traditional multi-cycle PIP process, which includes repeated polymer infiltration, crosslinking at elevated temperature in an inert environment, and pyrolysis at high temperature, repeated for multiple cycles. The second method used a modified multi-cycle process in which multiple infiltration and crosslinking cycles were performed prior to a single pyrolysis cycle, with the goal of reducing processing time and improving manufacturing scalability. Samples produced using both processing methods were evaluated using weight analysis, ceramic yield calculations, oxidation testing, scanning electron microscopy (SEM), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), and mechanical testing. SEM was used to evaluate ceramic coating formation and fiber surface coverage, while FTIR and XRF were used to confirm polymer-to-ceramic conversion and ceramic phase formation. Oxidation resistance was evaluated by exposing samples to elevated temperature in air and measuring weight retention. Mechanical testing was conducted to compare stiffness, strength, and toughness of ceramic-coated fiber bundles to uncoated carbon fiber bundles. Results showed that increasing infiltration cycles increased ceramic matrix formation and improved oxidation resistance for both SiCN and SiBCN ceramic matrix composites. The modified multi-infiltration single-pyrolysis process produced composites with comparable ceramic matrix formation, oxidation resistance, microstructure, and mechanical behavior while significantly reducing the number of high-temperature pyrolysis cycles required. This reduction in furnace processing time represents a significant advantage for manufacturing scalability and production efficiency. Overall, this research demonstrates that multi-cycle infiltration followed by a single pyrolysis cycle is a viable alternative to traditional multi-cycle PIP processing and offers a more scalable manufacturing method for polymer-derived ceramic matrix composites for high-temperature structural applications.