Manufacturing isotropic carbon fibre preforms for multilayered silicon carbide composites with a pyrolytic carbon interphase

In the present work, isotropic carbon fibre preforms with self-supporting porous structures and random orientation were fabricated through a wet papermaking filtration method. Then pyrolytic carbon (PyC) and silicon carbide (SiC) were alternatively infiltrated into the as-laminated preforms to obtain the multilayer composites (C_sf/SiC-C) by the chemical vapor infiltration method. The effects of fibre content and soft-hard multilayer matrix on mechanical properties were investigated. With the increase of fibre content, the bending strength and fracture toughness of composites without PyC inside matrix (C_sf/SiC) increase while the porosity decreases. When the fibre content is 10.2, 11.8, and 13.9 vol%, the bending strength of C_sf/SiC composites reaches the values of 170, 182, and 203 MPa, respectively. Furthermore, the composites exhibit good isotropy in mechanical properties. A model related to random orientation fibres was established to illustrate the relationship between bending strength, fibre content and porosity, which shows good accordance with the experimental data. Compared with C_sf/SiC, C_sf/SiC-C shows maximum increases of 17.3% and 18.3% in bending strength and fracture toughness, respectively. It is indicated by micrographs that the energy is consumed when cracks deflect by random orientation fibres and in multilayer of PyC and SiC, which provides a major contribution for improvement in mechanical properties.