Fabrication of Advanced C/C Composites by a Hybrid Process of CVI/Liquid Precursor Impregnation

Abstract

ABSTRACTFabrication process of advanced C/C composites was developed by combining the CVI and liquid impregnation-pyrolysis processes. Time-controlled temperature-gradient (TC-TG-) CVI process was developed to accelerate the carbon matrix deposition in the C-fiber preform within relatively short process-time. The temperature gradient in the preform was changed according to a controlled program. The present TC-TG-CVI process gave twice as much weight gain as that of the conventional steady TG-CVI process. The CVI process, however, showed limitation to fill up the large pores between the bundles. Liquid impregnation-pyrolysis was, therefore, carried out after the TC- TG-CVI process to improve the infiltration of these pores. Polycarbosilane (PCS) with the yield of about 50 wt% was used as the liquid precursor to form a SiC-rich matrix to improve the oxidation-resistance. SiC matrix was observed in the pores between bundles after pyrolysis of PCS. The weight gain after pyrolysis was found to be nearly saturated after 10 cycles of the impregnation-pyrolysis process.