Preparation and Properties of Density Gradient Carbon/Carbon Composites

Density gradient carbon/carbon composites were infiltrated using forced flow thermal gradient chemical vapor infiltration in the range of 1000-1250 ℃. Flexural strength and thermal conductivity were determined by 3 point bending test and laser flashing method. Microstructure of deposited pyrolytic carbon and morphology of fracture surface were observed by polarized light microscopy and scanning electron microscopy. The results show that maximal density of upper part of the composites was 1.65g·cm-3, while miniumum density of bottom part was 1.10g·cm-3, and obvions density gradient was found. Flexural strength and coefficient of thermal conductivity increased with the increase of density of the composites. The deposition temperature had a great impact on the microstructure of the pyolytic carbon. A higher temperature was favourable for the formation of rough layer hydrocarbon, while a lower temperature was favourable for the formation of smooth layerhy drocarbon.