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

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 (CH 4 ) gas. The SiC whisker content was 15 vol% in the Si 3 N 4 matrix, which contained sintering additives of 3 mol% α-Al 2 O 3 and Y 2 O 3 each. The sintered bodies were obtained by hot-pressing at 1800°C for 1 or 1.5 h in N 2 atmosphere under the applied load of 30 MPa. 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 Si 3 N 4 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 Si 3 N 4 matrix in portions depending upon reacted quantity to have direct bonding between the Si 3 N 4 matrix and SiC whiskers. The interfacial condition for toughening is improved by this present carbon coating method.