A high-strength SiCw/SiC-Si composite derived from pyrolyzed rice husks by liquid silicon infiltration

A high-strength SiC composite with SiC whiskers (SiCw) as reinforcement has been fabricated by liquid silicon infiltration (LSI) using pyrolyzed rice husks (RHs) as raw material. RHs were coked and pyrolyzed subsequently at high temperature to obtain a mixture containing SiC whiskers, particles, and amorphous carbon. The pyrolyzed RHs were then milled and modeled to preforms, which were then used to fabricate biomorphic SiCw/SiC-Si composites by liquid silicon infiltration at 1,450, 1,550, and 1,600 A degrees C, respectively. Dense composite with a density of 3.0 g cm(-3) was obtained at the infiltration temperature of 1,550 A degrees C, which possesses superior mechanical properties compared with commercial reaction-sintered SiC (RS-SiC). The Vickers hardness, flexure strength, elastic modulus, and fracture toughness of the biomorphic SiCw/SiC-Si composite were 18.8 +/- A 0.6 GPa, 354 +/- A 2 GPa, 450 +/- A 40 MPa, and 3.5 +/- A 0.3 MPa m(1/2), respectively. Whereas the composites obtained at the other two infiltration temperatures contain unreacted carbon and show lower mechanical properties. The high flexure strength of the biomorphic composite infiltrated at 1,550 A degrees C is attributed to the dense structure and the reinforcement of the SiC whiskers. In addition, the fracture mechanism of the composite is also discussed.