Mechanical enhancement of C/C composites via the formation of a machinable carbon nanofiber interphase

C/C composites with improved mechanical strength were synthesized using a filler constituted by a carbon felt covered with catalytically grown carbon nanofibers (CNFs) and a carbonaceous matrix generated by the pyrolysis of a phenolic resin. First, the synthesis method of the filler allows the homogeneous deposition and anchorage of CNFs on the host microfilaments at a rapid densification rate. Carbon nanofibers grown this way lead to the formation of numerous micro- and nanobridges between the microfilaments, conferring a significant improvement of the mechanical resistance of the CNF/C system allowing one to tailor its dimensions and shape. Thus, further fabrication of C/C composites can be achieved: the CNF/microfilament structure was infiltrated with a phenolic resin and carbonized at 650 degrees C to generate a carbonaceous matrix by thermal decomposition. Similar experiments on the microfilaments carried out at the same synthesis time, without catalyst and at higher reaction temperatures led to the deposition of a pyrolytic carbon sheath and to poor mechanical enhancements. This clearly indicates the advantage of using CNF growth as an efficient densification process before infiltration. Such C/C composites exhibit high-quality bonding between the two carbon phases, the matrix and the CNF/microfilament filler, via the formation of a considerable amount of CNF interphase. (c) 2007 Elsevier Ltd. All rights reserved.