LIU Yiyang ¹, WANG Zihan ¹, HE Mei ², ZHANG Chengshuang ², XU Haidong ³, WANG Mingcun ¹

(1. School of Chemistry, Beihang University, Beijing 102206, China; 2. Xi'an Aerospace Composites Research Institute, Xi'an 710025, Shaanxi, China; 3. Technology Innovation Service Center of Menyin, Linyi 276200, Shandong, China)

Extended abstract:[Background and purposes] Ceramic matrix composites (CMCs) exhibit excellent properties, such as high temperature resistance and corrosion wear resistance, thus finding wide applications in aerospace and other fields. Non-oxide CMCs, with SiC/Si₃N₄ matrix and carbon fiber reinforcement, can withstand over 2000 ℃ in inert environments. Preparation methods include CVI (low temperature but high cost), PIP (shorter cycle, more economical), SHP (simple process but fiber damage) and RMI (suitable for complex shapes but side reactions). Ceramic precursors (e.g., polysilane, polycarbosilane) are key for PIP and prepreg hot-pressing, requiring processability and high ceramic yield. This study is aimed to focus on low-cost rapid forming of CMCs using thermosetting polysilazane precursor, achieving atmospheric low-temperature preparation via one-step hot-pressing-pyrolysis of carbon fiber web prepreg, while analyzing mechanical and friction properties for high-kinetic brake materials.[Methods] A cost-effective process was developed to produce shortcut-carbon-fiber web reinforced SiC composites. Preceramic slurry with no solvent was applied as matrix, composing of vinyl-containing polysilazane (PSZ-3112) as adhesive, SiC powders as additives and 1,6-diisocyanatohexane (HDI) as curing agent. Short-cut carbon fiber web was applied as reinforcement. The ceramic composites were readily prepared through five steps of prepregs, gelation, stacking, hot press and pyrolysis.[Results] The thermal curing of ViPSZ was accelerated by HDI, while the initial temperature and peaking temperature of exotherm were found at 83.5 ℃ and 118 ℃ respectively. The parameters of hot press were defined as follows: the mass ratio of Cw and slurry at 1:10, the mass ratio of SiC:ViLSZ:HDI at 1.0:1.0:0.2, primary gelation at natural condition, processing pressure at 10 MPa and processing temperature at 150 ℃. After pyrolysis, the ceramic composites remained their original shape, the density was >1.6 g·cm⁻³ and the good adhesion of interface between ceramic matrix and carbon fibers was ascertained by the SEM results. The friction coefficient was determined to be 0.25–0.40, while the wear rate was as low as 0.12–0.23 cm³·N⁻¹·m⁻¹. Therefore, the ceramic composites could be prepared by using the rapid hot-press process of polysilazane's carbon-fiber-web prepregs.[Conclusions] A solvent-free slurry was prepared by blending vinyl polysilazane (ViLSZ) as the matrix resin, silicon carbide (SiC) powder, and hexamethylene diisocyanate (HDI) curing agent. Short-cut carbon fiber web (Cw) was used as the reinforcement, while the ceramic matrix composites were successfully fabricated through processes including prepreg coating, pre-gelation, lamination, hot-pressing, and high-temperature pyrolysis. The HDI curing agent effectively promoted the curing reaction of ViLSZ with a curing peak at 118 ℃, which significantly improved the rheological properties of the slurry. The optimized hot-pressing parameters for prepreg (molding) determined by conditional tests were as follows: mass ratio of Cw to slurry 1:10, mass ratio of SiC:ViLSZ:HDI 1.0:1.0:0.2, room-temperature gelation for 48 h, hot-pressing pressure of 10 MPa, and hot-pressing temperature of 150 ℃. After high-temperature sintering, the composites exhibited a density ≥1.75 g·cm⁻³, with strong interfacial bonding and slight debonding between the matrix and fibers. Friction coefficient of the Cw-reinforced SiC ceramic matrix composites ranged from 0.25 to 0.40, while the wear rate was as low as 0.12–0.23 cm³·N⁻¹·m⁻¹, indicating excellent tribological performance.

Key words: short-cut carbon fiber web; vinyl-contaning polysilazane; silicon carbide additives; hot-press process; ceramic-matrix composite