Bonding strength between fibers and matrices of ceramic matrix composites (CMCs) is of great importance for the fracture behavior and can be adjusted by appropriate fiber coatings. In this study, the continuous coating of SiBNC fibers with hexagonal boron nitride (h‐BN) by CVD from TMB in an atmospheric pressure reactor is presented. Prior to fiber coating, the effects of deposition parameters, e.g., deposition temperature, concentration of the precursor and ammonia addition, and gas‐flow rate are investigated on flat Si substrates, and the results are utilized for the fiber coating. Ammonia concentration has no influence on the deposition rate. A maximum deposition rate of 0.044 kg m−2 h−1 for static conditions and 0.040 kg m−2 h−1 for continuous conditions can be achieved, which is comparable to the literature. The depositions are characterized for their composition and structure. Smooth homogeneous coatings with a thickness of 180–250 nm are found on the fibers. High‐resolution transmission electron microscopy (HRTEM) of the coated SiBNC fibers reveals that the hexagonal BN with 5 nm basal planes is mainly randomly oriented.
The aim of this work is the coating of SiBNC fibers with hexagonal boron nitride (h-BN) for ceramic composite applications. h-BN is deposited from borazine in a vertical, hot-wall, atmospheric pressure (AP)CVD system. The effects of deposition parameters (e.g., temperatures, reactant concentrations, and gas velocity) on the deposition rates are investigated using Si (100) substrates statically placed at various positions in the reactor. The highest deposition rates are observed at 1090 8C. It is found that ammonia is necessary for a satisfying coating deposition and for low oxygen incorporation, though high concentrations decreased the deposition rate. The coating structures are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. Based on the results of static h-BN deposition on Si substrates, h-BN is continuously and homogenously coated on SiBNC multifilaments with a fiber draw speed of 5 m h
À1. The thickness of the coating on SiBNC fibers is 180-200 nm as measured by SEM. The h-BN coatings from our experiments have no influence on the mechanical strength of the SiBNC fibers.
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