Preparation and microstructure characterization of SiC/SiC joints reinforced by in-situ SiC nanowires

A novel two-step joining technology (pyrolysis and C-Si reaction bonding) to prepare in-situ SiC nanowires reinforced SiC/SiC joints were developed. The multi-component slurry consisting of polycarbosilane (PCS, preceramic polymer) and ferrocene (catalyst) were designed and optimized to join the sintered SiC ceramics. Microstructure of the joining layer after pyrolysis and joints after C-Si reaction bonding were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In addition, PCS-derived products and growth mechanism of SiC nanowires inside the joining layer were discussed. The results showed that 4 wt% castor oil and 3 wt% phenolic resin were proven to be the optimized dispersant content and binder content of the slurry to obtain the top-quality joining layer. With the increase of PCS content in the slurry, the generated SiC nanowires inside the joining layer became straight and diameter increased. After C-Si reaction bonding, the SiC nanowires were retained and distributed randomly in the joining layer. PCS-derived products after pyrolysis consisted of beta-SiC and free carbon, and later gradually increased with rise of pyrolysis temperature. The SiC nanowires inside the joining layer grew up following the Vapor-Liquid-Solid (VLS) mechanism and gaseous substances used for the growth were mainly comprised of CH4, SiH4 and CH3SiH3.