Densification kinetics and matrix microstructure of carbon fiber/carbon nanofiber/pyrocarbon composites prepared by electrophoresis and thermal gradient chemical vapor infiltration

Preforms were fabricated by the application of direct current fields for the alignment and network formation of carbon nanofibres in the needle-punched carbon fiber felts, and infiltrated by using the thermal gradient chemical vapor infiltration at the temperature of 1000 °C under the total pressure of 5 kPa. The voltage had a strong influence on the carbon nanofiber weight obtained in the preform. With the increase of the voltage, the carbon nanofiber content increased. The carbon nanofibers formed networks on the carbon fibers. When the voltage remained at 30 V, the carbon nanofibers were dispersed uniformly on the carbon fibers. However, when the voltage was larger than 60 V, the carbon nanofibers agglomerated themselves and coated the carbon fibers. The carbon nanofiber content has a strong influence on the temperature distribution and on the densification front existence, velocity and width. The achievable degree of pore filling in the carbon nanofiber-added preform at 30 V was the highest, while the carbon nanofiber-added preforms at 60 and 90 V could not be densified efficiently. The microstructure of pyrocarbon at different positions is discussed.