R. Naslain et al/Composites: Part A 30(1999)537-547 Fig 1. Nicalon/SiC microcomposites:(a)samp ing CVD-processing,(b)morphology of a SiC/BN/SiC microcomposite failed under tensile loading at room temperature showing fiber pull-out. contribution is to show how such model composites can be prepared and characterized, on the one hand, and to give the limits of the approach, on the other hand 2. Experimental SiC/SiC micro-or minl-composites comprise one straight single filament or a tow, respectively. Most experiments were performed with Si-C-O ex-polycarbosilane Nicalon fibers or Si-C oxygen-free Hi-Nicalon fibers, both display ing 500 filaments per yarn (with a filament diameter of 14 um)and being manufactured by Nippon Carbon. Some experiments were also conducted with high strength ex- Pan carbon fibers (filament diameter of 7 um). Micro 4≥s and minicomposites were fabricated according to I-CVI or pressure pulsed CVI (P-CVI)techniques, which have been described in detail elsewhere [1, 21]. In the preparation of minicomposite, the starting material was a length of the as- received multifilament yarn, slightly twisted and maintained in straight configuration with a ceramic holder. In that of a microcomposite, a length of one single filament was care- acted from the yarn and mounted on a ceramic holder with a high temperature cement, as shown in Fi 1. In a second step, the interphase was deposited onto the fiber surface from suitable gaseous precursors including: (i) hydrocarbons, such as CH4, C3 H8, C3H, for anisotropic pyrocarbon interphases; ( ii) BF3-NH3 or BCly-NH3-H2 mixtures for the deposition of boron nitride; (iii) hydrocar- bons and CHa SiCl, /H for multilayered(Pyc-SiC)n inter- phases and (iv)C3Hg-BCl3-H2 mixtures for composition graded C(B)interphases. The interphase, with an overall 186R thickness of a few 100 nm, was usually deposited(micro- composites)or infiltrated (minicomposites) by P-CVD/P- CVI rather than by conventional I-CVI, inasmuch as the Fig. 2. C/C minicomposites:(a) failure surface; (b)multiple matrix micro- former allows a better control of the morphology and texture acking, according to Ref. [24] of the interphase. As a matter of fact, complex multilayeredcontribution is to show how such model composites can be prepared and characterized, on the one hand, and to give the limits of the approach, on the other hand. 2. Experimental SiC/SiC micro- or mini-composites comprise one straight single filament or a tow, respectively. Most experiments were performed with Si-C-O ex-polycarbosilane Nicalon fibers or Si-C oxygen-free Hi-Nicalon fibers, both display￾ing 500 filaments per yarn (with a filament diameter of 14 mm) and being manufactured by Nippon Carbon. Some experiments were also conducted with high strength ex￾PAN carbon fibers (filament diameter of 7 mm). Micro and minicomposites were fabricated according to I-CVI or pressure pulsed CVI (P-CVI) techniques, which have been described in detail elsewhere [1,21]. In the preparation of a minicomposite, the starting material was a length of the as￾received multifilament yarn, slightly twisted and maintained in straight configuration with a ceramic holder. In that of a microcomposite, a length of one single filament was care￾fully extracted from the yarn and mounted on a ceramic holder with a high temperature cement, as shown in Fig. 1. In a second step, the interphase was deposited onto the fiber surface from suitable gaseous precursors including: (i) hydrocarbons, such as CH4; C3H8; C3H6, for anisotropic pyrocarbon interphases; (ii) BF3-NH3 or BCl3-NH3-H2 mixtures for the deposition of boron nitride; (iii) hydrocar￾bons and CH3SiCl3/H2 for multilayered (PyC-SiC)n inter￾phases and (iv) C3H8-BCl3-H2 mixtures for composition graded C (B) interphases. The interphase, with an overall thickness of a few 100 nm, was usually deposited (micro￾composites) or infiltrated (minicomposites) by P-CVD/P￾CVI rather than by conventional I-CVI, inasmuch as the former allows a better control of the morphology and texture of the interphase. As a matter of fact, complex multilayered 538 R. Naslain et al. / Composites: Part A 30 (1999) 537–547 Fig. 1. Nicalon/SiC microcomposites: (a) sample holder used during CVD-processing, (b) morphology of a SiC/BN/SiC microcomposite failed under tensile loading at room temperature showing fiber pull-out. Fig. 2. C/C minicomposites: (a) failure surface; (b) multiple matrix micro￾cracking, according to Ref. [24]