The conversion of all carbon preforms to dense SiC by liquid infiltration can become a low-cost and reliable method to form SiC-Si composites of complex shape and high density. Reactive sintered silicon carbide (RBSC) is prepared by covering Si powder on top of 0.5-5.0 wt% Y2O3-added carbon preforms at 1,450 and 1,500°C for 2 hours; samples are analyzed to determine densification. Reactive sintering from the Y2O3-free carbon preform causes Si to be pushed to one side and cracking defects occur. However, when prepared from the Y2O3-added carbon preform, an SiC-Si composite in which Si is homogeneously distributed in the SiC matrix without cracking can be produced. Using the Si + C = SiC reaction, 3C and 6H of SiC, crystalline Si, and Y2O3 phases are detected by XRD analysis without the appearance of graphite. As the content of Y2O3 in the carbon preform increases, the prepared RBSC accelerates the SiC conversion reaction, increasing the density and decreasing the pores, resulting in densification. The dense RBSC obtained by reaction sintering at 1,500 oC for 2 hours from a carbon preform with 2.0 wt% Y2O3 added has 0.20% apparent porosity and 96.9% relative density.

The conversion of carbon preforms to dense SiC by liquid infiltration is a prospectively low-cost and reliable method of forming SiC-Si composites with complex shapes and high densities. Si powder was coated on top of a 2.0wt .% Y2O3-added carbon preform, and reaction bonded silicon carbide (RBSC) was prepared by infiltrating molten Si at 1,450oC for 1-8 h. Reactive sintering of the Y2O3-free carbon preform caused Si to be pushed to one side, thereby forming cracking defects. However, when prepared from the Y2O3-added carbon preform, a SiC-Si composite in which Si is homogeneously distributed in the SiC matrix without cracking can be produced. Using the Si + C → SiC reaction at 1,450oC, 3C and 6H SiC phases, crystalline Si, and Y2O3 were generated based on XRD analysis, without the appearance of graphite. The RBSC prepared from the Y2O3-added carbon preform was densified by increasing the density and decreasing the porosity as the holding time increased at 1,450oC. Dense RBSC, which was reaction sintered at 1,450oC for 4 h from the 2.0wt.% Y2O3-added carbon preform, had an apparent porosity of 0.11% and a relative density of 96.8%.

Multidirectional reinforcement is aimed primarily at overcoming interlaminar weakness, hence a major interest lies in the mechanical properties of multidirectional carbon/carbon composites. Mechanical properties depend on the type of carbon fiber, the size of the fiber bundle, the spacing of the bundles, the angles of the bundles relative to the axes of the block, and matrix formation. In the present studies, PAN based carbon fiber preforms manufactured different size of unit cell have been prepared. Densification of these used high pressure infiltration and carbonization technique with coal tar pitch as matrix precursor was carried out. Scanning electron microscopy has been used to study the fracture behavior of composites. The size of unit cell of the preforms has considerably affected on the flexural properties as well as microstructure of the carbon/carbon composites.