w, Yang et al. /Ceramics International 31(2005)47-5 Graphite Fibe laver 10nm Fig. 2. SEM images of the cross-section(a)and intra-fiber bundle pores Fig. 4. HRTEM image showing the granular graphite structure of the (b)of the composite interleave lated selected area electron diffraction(SAD)patterns. The fiber has a poly-crystal B-Sic structure, as is well known. radially away from the fiber. Between the fiber and the ma The tem image and the sad of the matrix indicate a trix, the image clearly shows the existence of an interfacial highly-crystal p-SiC structure with the growing directio layer. The SAD taken from this area indicates a graphite structure, which is confirmed by the HrTEM image(Fig 4) During the CVI process, following basic chemical reactions occurred [13 C2HsSiCl3 +H2= SiC 3HCI+ CH4 Extra carbon was produced from above second reactions known from the experimental section, the Hi-Nicalon fibers as-received ones. No fiber before the CVI process. Therefore, it is believed that the graphite layer was formed during the CVi process owing to the extra carbon from above reactions The thickness of the graphite layer is 180 nm. The detailed mechanism of the formation of the graphite interlayer currently remains un lear. However, the thickness of this graphite layer showed some process conditions dependence, especially at the ini- tial stage of the CVI. As mentioned before, compliant in- terlayer()is necessary for tough SiC/SiC composites, this study indicates that ETS might be a good source material for the fabrication of CVI-SiC/SiC composites with automatic formation of graphite interlayer, provided further studies on A: Hi-NicalonM fiber the control the thickness of this layer B: Graphite layer C: CVI-matrix 3.2. Fracture behavior and flexural strength Fig. 5 shows the load-displacement curves, which dis- plays several common features among the three specimens an initial linear region, reflecting the elastic response of the Fig 3. TEM image and SAD patterns of the fiber, the matrix, and the materials, followed by a non-linear domain of deformation, due to the matrix cracking, interfacial debonding and fiberW. Yang et al. / Ceramics International 31 (2005) 47–52 49 Fig. 2. SEM images of the cross-section (a) and intra-fiber bundle pores (b) of the composite. lated selected area electron diffraction (SAD) patterns. The fiber has a poly-crystal -SiC structure, as is well known. The TEM image and the SAD of the matrix indicate a highly-crystal -SiC structure with the growing direction Fig. 3. TEM image and SAD patterns of the fiber, the matrix, and the interlayer. Fig. 4. HRTEM image showing the granular graphite structure of the interlayer. radially away from the fiber. Between the fiber and the ma￾trix, the image clearly shows the existence of an interfacial layer. The SAD taken from this area indicates a graphite structure, which is confirmed by the HRTEM image (Fig. 4). During the CVI process, following basic chemical reactions occurred [13]. C2H5SiCl3 + H2 = SiC + 3HCl + CH4 CH4 = C + 2H2 Extra carbon was produced from above second reactions. As known from the experimental section, the Hi-Nicalon fibers are as-received ones. No fiber coating was pre-deposited before the CVI process. Therefore, it is believed that the graphite layer was formed during the CVI process owing to the extra carbon from above reactions. The thickness of the graphite layer is ∼180 nm. The detailed mechanism of the formation of the graphite interlayer currently remains un￾clear. However, the thickness of this graphite layer showed some process conditions dependence, especially at the ini￾tial stage of the CVI. As mentioned before, compliant in￾terlayer(s) is necessary for tough SiC/SiC composites, this study indicates that ETS might be a good source material for the fabrication of CVI-SiC/SiC composites with automatic formation of graphite interlayer, provided further studies on the control the thickness of this layer. 3.2. Fracture behavior and flexural strength Fig. 5 shows the load–displacement curves, which dis￾plays several common features among the three specimens: an initial linear region, reflecting the elastic response of the materials, followed by a non-linear domain of deformation, due to the matrix cracking, interfacial debonding and fiber