Carbon/carbon composites has been widely used in aerospace,weaponry and other fields with their excellent properties.However,the development of carbon/carbon composites has been limited by the high cost of carbon fiber preforms.Carbon foam has a three-dimensional network structure,and its ligaments show similar properties to carbon fibers,which can be used as the reinforcing phase to prepare carbon/carbon composites.In this paper,carbon foams with different carbon fiber volume contents(0vol%,1vol%,3vol%,5vol%,7vol%)were prepared as carbon/carbon composites preforms by using phenolic resin as the carbon source and NaCl as the pore-forming agent,and the carbon/carbon composites were prepared by using the rapid densification technique of thermal gradient chemical vapour infiltration(TG-CVI),which investigated the effects of carbon fiber content on the carbon fiber/carbon foam preform and its density,microstructure and mechanical properties after densi-fication.The effects of carbon fiber content on the density,microstructure and mechanical properties of the carbon fiber/carbon foam preform and its densification were investigated.The results showed that with the increase of carbon fiber content,the number of microcracks in the carbon fiber/carbon foam precast body increased significantly,the density gradually decreased from 0.51 g/cm3 to 0.31 g/cm3,and the compressive strength decreased from 51.33 MPa to 1.35 MPa,flexural strength decreased from 42.53 MPa to 6.32 MPa.The compressive and flexural strengths of the carbon/carbon composites were significantly increased after densifica-tion,up to 183.67 MPa and 123.46 MPa,respectively,while the density was 1.09 g/cm3,resulting in high specific strength.The thermal conductivity of the composites increased from 0.298 W/(m·K)(before densification)to 2.484 W/(m·K),an increase of 734%,which was attributed to the formation of a three-dimensional thermal conductivity network between the carbon fibers and pyrolytic carbon after densification.
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