MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF 3-DIMENSIONAL CARBON SILICON CARBIDE COMPOSITES FABRICATED BY CHEMICAL-VAPOR INFILTRATION/

Three-dimensional carbon/silicon carbide composites were fabricated by chemical vapor infiltration, and the microstructure and mechanical pr operties were investigated. For the composites (C/SiC) with no pyrolyt ic carbon interfacial layer, the mechanical properties (flexural stren gth, flexural elastic modulus, shear strength and fracture toughness) are increased with density of the composites. High density (rho =2.1 g cm(-3)) C/SiC composites exhibit high fracture toughness (16.5 MPa m( 1/2)) but brittle fracture behavior because of strong bonding between the fiber/matrix. Low density composites show non-catastrophic failure mode with bundle pull-out. The composites (C/PyC/SiC) with pyrolytic carbon interfacial layer exhibit good mechanical properties and a typi cal Failure behavior involving fiber pull-out and brittle fracture of sub-bundle. Microstructural observations and theoretical analysis reve al that the tortuosity and bottleneck effect of the pores and large mo lar mass of reactant agent (methyltrichlorosilane) are three key issue s to hinder the densification of composites. Cracks formed in the SiC matrix by thermal stress have two influences on the mechanical propert ies of the composites: to decrease mechanical properties and have some contribution on toughness and failure behavior by deflecting cracks. (C) 1998 Elsevier Science Ltd. All rights reserved.