Fabrication and mechanical properties of SiCw/MoSi2-SiC composites by liquid Si infiltration of pyrolyzed rice husk preforms with Mo additions

Dense SiC ceramic matrix composites containing SiC whiskers (Sic,) and MoSi2 phase (SiCw/MoSi2-SiC) are fabricated by a liquid Si infiltration (LSI) method. Pyrolyzed rice husks (RHs) containing SiC whiskers, particles and amorphous carbon are mixed with different amounts of Mo powder to form preforms for the infiltration. Microstructure and mechanical properties of the composites are studied. Fracture mode of the composites is discussed. Results show that the SiC whiskers and fine particles in the pyrolyzed RHs were preserved in the composites after the LSI process. The amorphous carbon and Mo powder in the preforms reacted with molten Si, forming SiC and MoSi2 in the composites. The presence of MoSi2 in the composite increases the elastic modulus but lowers the flexure strength. Content of MoSi2 of ca. 20 wt.% provides an enhanced fracture toughness of 4.1 MPa m(1/2) for the composite. But too large amount of MoSi2 caused crack formation in the composite. The compressive residual stress introduced by the formation of MoSi2 and SiC, and the de-bonding of the fine SiC particles and SiC whiskers from the residual Si phase are considered to favor the fracture toughness of the composites. (C) 2012 Elsevier Ltd. All rights reserved.