Effect of pyrocarbon content in C/C preforms on microstructure and mechanical properties of the C/C-SiC composites

Carbon fiber reinforced silicon carbide matrix (C/C-SiC) composites were prepared by liquid silicon infiltration (LSI) process, using four kinds of quasi-three-dimensional C/C preforms with the same fiber volume fraction (32%) but different pyrocarbon content (from ∼20% to ∼50%, in volume) filled by chemical vapor infiltration (CVI). The microstructure and mechanical properties of C/C-SiC composites have been investigated. X-ray diffractmeter (XRD) analysis results show the composites are composed of three phases of β-SiC, C and Si. With the increase of the pyrocarbon content in the C/C preforms, the content of formed silicon carbide in the C/C-SiC composites decreases but the residual pyrocarbon increases. Mechanical tests were performed to assess the role of the matrix and phase composition in the C/C-SiC composites. The results demonstrate that the flexural strength and shear strength of the composites increase gradually as the increase of the content of residual pyrocarbon. The flexural and shear strength of the C/C-SiC composite produced of the C/C preform with pyrocarbon content of ∼42 vol.% reached the highest value.