Enhanced Mechanical Property of RMI C/SiC Composites with Optimized Porous Carbon Structure by Heat Treatment

Abstract C/SiC composites were fabricated by reactive melt infiltration (RMI) using porous C/C preforms as the skeleton, followed by the infiltration of molten silicon. A convenient technique of heat treatment in the range of 1500 to 2400 oC was applied to modify the porous carbon structure. The effects of heat treatment on the porous C/C preforms and the as-synthesized C/SiC composites were investigated in detail. The results show that the optimal porous carbon structure could be obtained after heat treatment at 1500 oC. After 1500 oC heat treatment, the median pore size and porosity of the porous C/C preform were 9.3 µm and 13.65% respectively, which were in favor of the subsequent infiltration of molten Si. The C/SiC composites with the optimized porous carbon structure showed a dense and uniform morphology without obvious cracks. Their bending strength could be up to 276 MPa, which was 28% higher than that of the C/SiC composites with untreated C/C preforms. However, with the increasing heat treatment temperature (2400 oC), the bending strength of the as obtained composites began to decrease because of the degradation of in-situ fiber strength. The optimized C/SiC composites exhibited a typical pseudo-plastic fracture behavior with obvious fiber pull-out. The improved mechanical property could be ascribed to the lower porosity of composites, the higher in-situ strength of fibers and the reduced matrix cracks.