研究目的
To determine appropriate processing conditions for the BN interphase and the SiC/Si3N4 composites, and to investigate the relationships between processing parameters, mechanisms controlling the kinetics of BN CVI, and the morphology of the boron nitride layer.
研究成果
An optimized BN interphase with lamellar texture was developed for Hi-Nicalon fiber-reinforced composites. Multilayer coatings with isotropic and anisotropic layers were achieved, providing protection and mechanical fuse properties. Crack deflection was observed in anisotropic layers, improving composite durability. Fiber mechanical properties were preserved after coating. The quality of fiber-interphase and matrix-interphase interfaces is crucial for performance.
研究不足
The gaseous environment (BF3) can be corrosive to SiC fibers, potentially degrading them. Heterogeneity in deposit thickness may occur in large preforms. The specific roles of BF3 and NH3 in BN crystallization are not fully determined. Optimization of temperature gradients and gas compositions is needed for better control.
1：Experimental Design and Method Selection:
The study used chemical vapor infiltration (CVI) with BF3/NH3 precursors to deposit BN interphase on Hi-Nicalon SiC fibers. Experiments were conducted under static and dynamic conditions with controlled temperature, pressure, gas flow rates, and fiber displacement to study kinetics and structure.
2：Sample Selection and Data Sources:
Hi-Nicalon SiC fibers from Nippon Carbon/NGS Advanced Fibers Co. Ltd. were used. Data were obtained from SEM, TEM, Raman spectrometry, and X-ray diffraction analyses.
3：List of Experimental Equipment and Materials:
CVI reactor with hot wall furnace, graphite susceptor, silica tube, induction heating, spools for fiber winding, gases (BF3, NH3, Ar), Hi-Nicalon SiC fibers.
4：Experimental Procedures and Operational Workflow:
Fibers were wound on spools and moved through the reactor; CVI was performed with variations in temperature, pressure, gas composition, and fiber displacement rate; deposits were analyzed for morphology and structure.
5：Data Analysis Methods:
SEM for morphology, TEM for cross-section analysis, Raman spectrometry and X-ray diffraction for structure and anisotropy, using Scherrer equation for crystallite size determination.
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