Effect of preform density on densification rate and mechanical properties of carbon/carbon composites

The relationship among preform density, densification rate and mechanical properties of carbon/carbon composites was investigated. The samples were prepared by using isothermal chemical vapor infiltration, with natural gas as precursor and hydrogen as carrier and dilutant gas. Three kinds of carbon fabric with density of 0.4, 0.5, and 0.6 g/cm3, were used as preforms. The textural of pyrolytic carbons were observed by polarized light microscopy, and a flexure test was applied to investigate the influence of preform density on the flexural properties of the carbon/carbon composites. The results show that densification rate increase with preform density increasing in the first 50 h, while in the last 450 h, densification rate reduce with the increase of preform density. Low density of preform is in favor of obtaining the multilayered pyrocarbon. The samples prepared from using preform density of 0.5 g/cm3 have the intermediate density variations with position (about 0.014 g/cm3), and possess the highest flexure strength and modulus, while the samples with preform density of 0.4, 0.6 g/cm3 have the lower flexure strength and modulus due to lower density of preform and higher porosity.