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Micro-Structure and Properties of SiC_w/SiC Composites Manufactured by CVI

Author: WangJing
Tutor: ZhangLiTong
School: Northwestern Polytechnical University
Course: Materials Science
Keywords: chemical vapor infiltration (CVI) granulation SiC_w/SiC mini composites microstructure SiC_w/SiC composites relative density hardness fracture toughness
CLC: TB332
Type: Master's thesis
Year: 2007
Downloads: 277
Quote: 1
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Abstract


SiC ceramics is an excellent kind of high temperature material, for its resistance to high-temperature, oxidation resistance, ablation resistance and its low density, high specific strength, high specific modulus etc, but its brittleness and poor reliability of performance limit its wide applications. Adopting SiC whisker reinforcing SiC based ceramic composites is an effective method to solve high-temperature application. The high manufacturing temperature of sintering and the adding of sintering agents can damage the whiskers. However, Chemical Vapor Infiltration (CVI) can make up the shortage, and will be a potential method preparing whisker reinforced high purity SiC ceramic based composites at low temperature.The SiC_w/SiC mini composites materials manufactured by Chemical Vapor Infiltration (CVI) process was studied in this thesis first, which will guide the structure design and manufacturing process of the bulk composite materials. The SiC_w/SiC mini composites materials prepared by the whisker pellets with certain granularity by CVI process and the whisker partials are manufactured by PVA and Sol-Gel separately. Micro-hardness test combined with SEM technical are used to calculate the micro-hardness and analysis the fracture toughness, the research results will be the foundation for the strengthening and toughening designation, and the fabrication of the bulk composites. A compressed whisker preform is prepared by the whisker pellets granulated by PVA, then SiC_w/SiC bulk composites are manufactured by densify the whisker preform through CVI. The microstructure of the SiC_w/SiC bulk composite is analyzed by the SEM and TEM, the strength was test through the three-point bending method, the single edge notch beam method was applied to test the fracture toughness. The main research process and results are as follow:(1) The influences no the microstructure and performances of SiC_w/SiC mini composites caused by the whisker’ volume ratio, different granulation methods and the process conditions of CVI are studied. The results indicate: The whisker volume ratio, the whisker’ volume ratio, the granulation method and the substrate for deposition have a significant impact on the microstructure of SiC_w/SiC mini composites. The SiC_w/SiC mini composites which are much denser and more homogeneous are prepared by the PVA granulation with a whisker volume fraction of about 42%, and the carbon cloth was used as the substrate for deposition. The diameter of the closed pores are

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