Fast densification of thick-walled carbon/carbon composite tubes using electrically coupled chemical vapor infiltration

Rapid densification of thick-walled carbon/carbon (C/C) composite tubes by electrically coupled chemical vapor infiltration (EC-CVI) was investigated. The bulk densities and pore sizes of the C/C composites after different densification periods were measured. The results show that C/C composites were able to be densified by EC-CVI rapidly and efficiently. A thick-walled C/C composite tube, whose outer diameter, inner diameter and height was 240, 60 and 200 mm, respectively, was able to be densified to 1.71 g/cm3 after a densification time of 400 h. If the outer diameter and inner diameter were increased to 400 and 100 mm, respectively, the final density of the component reached 1.50 g/cm3 under the same experimental condition. After densified by EC-CVI, the amount of the pores with a size larger than 100 μm decreased significantly, and the porosity was even close to zero for the composites with a density of 1.62 g/cm3. It indicates that EC-CVI can effectively fill the large pores in the composites. In the densified composite by EC-CVI, the pyrocarbon on the carbon fibers presented a rough laminar and smooth laminar morphology dominantly. Finally, the densification mechanism of the C/C composites by EC-CVI was simulated by the fractal method.