J. Cent. South Univ. (2014) 21: 2590−2595 DOI: 10.1007/s11771-014-2217-8 Effect of nanofibers at surface of carbon fibers on microstructure of carbon/carbon composites during chemical vapor infiltration XIAO Peng(肖鹏), CHEN Jie(陈洁), XU Xian-feng(徐先锋), LU Xue-feng(卢雪峰) State Key Laboratory of Powder Metallurgy (Central South University), Changsha 410083, China © Central South University Press and Springer-Verlag Berlin Heidelberg 2014 Abstract: Before densification by chemical vapor infiltration, carbon or SiC nanofibers were grown on the surface of carbon fibers by catalytic chemical vapor deposition using electroplated Ni as catalyst. The modification and mechanism of nanofibers on the pyrocarbon deposition during chemical vapor infiltration were investigated. The results show that the nanofibers improve the surface activity of the carbon fibers and become active nucleation centers during chemical vapor infiltration. They can induce the ordered deposition of pyrocarbon and adjust the interface bonding between pyrocarbon and carbon fibers during the infiltration. Key words: carbon nanofiber; SiC nanofiber; pyrocarbon; interface bonding 1 Introduction Carbon fiber reinforced carbon matrix (C/C) composites are widely used in aerospace, fuel and energy industries mainly due to their low density, low thermal expansion, high thermal resistance and good strength retention at high temperature [1−3]. The excellent properties of C/C composites are influenced by the structure and distribution of carbon fibers and carbon matrix, and the bonding state between them is also the key factor [4−6]. The excellent properties of C/C composites are not only related to the performances of carbon fibers and matrix, but also dependent on the fiber/matrix interface. A good fiber/matrix interface is beneficial to load or thermal transfer, while a weak interface may impair the integrity of composites. Therefore, fiber surface modification is widely applied in C/C composites to improve the surface activity of fiber and the bonding state between fiber and matrix [7−8]. Nanofibers have aroused great interest because of their particular quasi-one-dimensional structure [9−10]. Nanofibers have been introduced to modify fiber surface and lots of further researches have been made [11−13]. Nanofibers on carbon fibers can decrease the surface defects and increase surface activity of carbon fibers, which will in turn influnce the deposition of pyrocarbon (PyC) and the interface bonding during chemical vapor infiltration (CVI). In this work, carbon nanofiber (CNF) and SiC nanofiber (SiCNF) were prepared on the surface of carbon fibers by catalytic chemical vapor deposition (CCVD) using electroplated Ni as catalyst. The modification and mechanism of CNF and SiCNF on carbon fibers and PyC deposition during CVI were investigated deeply. 2 Experimental 2.1 Material preparation Unidirectional carbon preforms were made from T700 polyacrylonitrile-based carbon fibers. Ni particles were uniformly distributed on the surface of carbon fibers by electroplating using 5% nickel sulfate as electrolyte. After catalysts were well prepared in the two carbon preforms, one preform was ready for CNF growth and the other was for SiCNF growth by CCVD. For CNF growth, C 3 H 6 was carbon source gas and N 2 was dilution gas, and the volume ratio of C 3 H 6 :N 2 was 2:3. For SiCNF growth, methyl-trichlorosilane (MTS) was SiC source gas, Ar was dilution gas and H 2 was carrier gas, and the volume ratio of MTS:Ar:H 2 was 1:2:3. After the growth of nanofibers on the surface of carbon fibers, preforms were densified by CVI to get CNF-modified C/C composite (DC) and SiCNF-modified Foundation item: Project(12JJ6051) supported by the Natural Science Foundation of Hunan Province, China; Project(2011CB605806) supported by the National Basic Research Program of China Received date: 2013−03−25; Accepted date: 2013−07−12 Corresponding author: CHEN Jie, Associate Professor, PhD; Tel: +86−731−88830131; Fax: +86−731−88830131; E-mail: chenjiecsu@163.com