Preparation and mechanical properties of carbon fiber reinforced (BC _x-SiC)_n multilayered matrix composites

A boron doped carbon materials (BC _x ) was prepared by chemical vapor deposition and a 3D (BC _x -SiC) _n multilayered matrix composite reinforced by carbon fiber, C/(BC _x -SiC) _n , was prepared by chemical vapor infiltration (CVI). XPS and SEM results showed that the BC _x matrix had a boron content of 15∈at.% and exhibited a very finely laminated structure. XRD analysis showed the BC _x matrix was mainly carbon with B₄C crystals in it. SEM and EDS results showed that the BC _x layers and the SiC layers were deposited within the interspaces of fiber bundles, alternately arranged and paralleled to each other as designed. The fracture energy of the composite was about 16.8 KJ m^-2. Flexural strength-displacement curve showed a remarkable metal-like yielding stage. Multiple fracture microstructures were induced by the multilayered matrix, such as delaminations of the multilayered matrix, deflections and propagations of cracks spread in the multilayered matrix layer by layer and long pullout of fiber bundles together with fiber clusters with multi-step pull-out structures. It was suggested that these special fracture behaviors absorbed a great deal of energy during the stress increasing and released the stress concentration, in this way, the toughness of the materials was improved.