Toughening Si<SUB>3</SUB>N<SUB>4</SUB>/SiC-Whisker Composite by <I>in-situ</I> Reaction to Control Whisker-Matrix Interface

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  • Yanai Tomohiro
    School of Mechanical Engineering, Nagaoka University of Technology
  • Ishizaki Kozo
    School of Mechanical Engineering, Nagaoka University of Technology

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  • Toughening Si3N4/SiC-Whisker Composite by in-situ Reaction to Control Whisker-Matrix Interface
  • Toughening Si3N4 SiC Whisker Composite

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Abstract

Controlling the interfacial conditions between the matrix and whiskers is critical to toughen whisker reinforced ceramic (WRC) composites. The interface was controlled by coating carbon on the SiC whisker surface in the present work. The carbon was coated by thermal decomposition of methane (CH4) gas. The SiC whisker content was 15 vol% in the Si3N4 matrix, which contained sintering additives of 3 mol% α-Al2O3 and Y2O3 each. The sintered bodies were obtained by hot-pressing at 1800°C for 1 or 1.5 h in N2 atmosphere under the applied load of 30 MPa.<BR>The bending strength and the fracture toughness are increased by the carbon coating. The coated carbon and the silicon oxide impurity phase on SiC whiskers and the Si3N4 surface reacts during hot pressing to form β-SiC on the whisker surface. The newly formed SiC phase is confirmed by TEM observation and electron diffraction analysis. The amount of the glassy interface phase is reduced by the in-situ SiC forming reaction, and eliminated at the interface of SiC whiskers and the Si3N4 matrix in portions depending upon reacted quantity to have direct bonding between the S3N4 matrix and SiC whiskers. The interfacial condition for toughening is improved by this present carbon coating method.

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