Availableonlineatwww.sciencedirect.com SCIENCE PHYSICS ANI MIsTRY F SOLIDS ELSEVIER Journal of Physics and Chemistry of Solids 66(2005)551-554 Fabrication of Sic fiber reinforced Sic composite by chemical vapor infiltration for excellent mechanical properties N. Igawa*, T. Taguchi T. Nozawa, L.L. Snead, T Hinoki, J.C. McLaughlin, Y Katoh, S Jitsukawa, A Kohyama Japan Atomic Energy Research institute, Tokai-mura, Ibaraki-ken 319-1195, Japan Oak Ridge National Laboratory, Oak Ridge, TN 37830-6146, USA Kyoto University, Gokasho, Uji-shi, Kyoto fit 611-0011, Japan Accepted 19 June 2004 The process optimization for the forced-flow/thermal gradient chemical vapor infiltrated Sic based composites with an advanced SiC fiber(Tyranno SA)was carried out. The new SiC/SiC composites had a lower porosity and the uniform distribution of pores compared with conventional CVI. The uniform interphases between SiC fibers and matrix could be obtained by reversing the gas-fiow direction mid-way through the coating process. The tensile strength was slightly increased with the thickness of carbon interphase in the range of 20-250 nm. It was found that the fabric layer orientation and multilayer SiC/C interphase were very effective to improve the mechanical properties C 2004 Elsevier ltd. all rights reserved Keywords: A. Ceramics: A. Interface; B. Vapour deposition 1. Introduction excellent interfacial shear strength and ductility between fiber and matrix which cause high mechanical properties Silicon carbide has high strength and stability at high Among the various fabrication processes of SiC/SiC, the temperature and low induced radioactivity after neutron forced-flow/thermal gradient chemical vapor infiltration irradiation [1]. Though monolithic SiC is extremely brittle (FCVI) method is one of the best techniques to fabricate with low toughness, continuous SiC fiber reinforced Sic the SiC/SiC for fusion applications because this method matrix composites(SiC/SiC) significantly improve these produces a highly pure, stoichiometric, crystalline B-SiC properties and therefore are attractive candidate materials for matrix with low thermal stress which minimizes fiber fusion reactor structural applications [2, 3]. Moreover, high- damage during fabrication [6]. On the other hand, Sic stalline and near -stoichiometric sic fibers including matrix in SiC/SiC fabricated by the CVI method has low Hi-Nicalon Type S and Tyranno SA retain superior density and poor homogeneity, which cause the degradation mechanical properties after oxidation at high temperature of the mechanical and thermal properties. In this study, we and neutron irradiation compared with conventional carried out the optimization of this process to obtain higher advanced fibers are expected to have better mechanical ical properties of SiC/Sic. We also studied the effects of the properties For SiC/SiC composites, the interphase between carbon and multilayer SiC/carbon interphase on the mech fiber and matrix is very important to improve the toughness anical properties. [2]because the optimized interphase brings the deflection of cracks at the interphase, fiber pullout during the fracture, 2. Experimental procedure Corresponding author. Tel: +81 29 282 6099: fax:+8129 284 3813 We adopted two advanced SiC fiber fabrics as preforms E-mail address: igawa@maico. tokai jaeri. go. jp(N. Igawa). 2D-plain weave of Tyranno SA(Ube Industries, Ube, Japan) 0022-3697/S. see front matter 2004 Elsevier Ltd. All rights reserved doi:10.1016/jpcs.200406.030Fabrication of SiC fiber reinforced SiC composite by chemical vapor infiltration for excellent mechanical properties N. Igawaa,*, T. Taguchia , T. Nozawab , L.L. Sneadb , T. Hinokic , J.C. McLaughlinb , Y. Katohb , S. Jitsukawaa , A. Kohyamac a Japan Atomic Energy Research Institute, Tokai-mura, Ibaraki-ken 319-1195, Japan b Oak Ridge National Laboratory, Oak Ridge, TN 37830-6146, USA c Kyoto University, Gokasho, Uji-shi, Kyoto-fu 611-0011, Japan Accepted 19 June 2004 Abstract The process optimization for the forced-flow/thermal gradient chemical vapor infiltrated SiC based composites with an advanced SiC fiber(Tyranno SA) was carried out. The new SiC/SiC composites had a lower porosity and the uniform distribution of pores compared with conventional CVI. The uniform interphases between SiC fibers and matrix could be obtained by reversing the gas-flow direction mid-way through the coating process. The tensile strength was slightly increased with the thickness of carbon interphase in the range of 20–250 nm. It was found that the fabric layer orientation and multilayer SiC/C interphase were very effective to improve the mechanical properties. q 2004 Elsevier Ltd. All rights reserved. Keywords: A. Ceramics; A. Interface; B. Vapour deposition 1. Introduction Silicon carbide has high strength and stability at high temperature and low induced radioactivity after neutron irradiation [1]. Though monolithic SiC is extremely brittle with low toughness, continuous SiC fiber reinforced SiC matrix composites (SiC/SiC) significantly improve these properties and therefore are attractive candidate materials for fusion reactor structural applications [2,3]. Moreover, high￾crystalline and near-stoichiometric SiC fibers including Hi-Nicalon Type S and Tyranno SA retain superior mechanical properties after oxidation at high temperature and neutron irradiation compared with conventional SiC-based fibers [4,5], therefore the composites with these advanced fibers are expected to have better mechanical properties. For SiC/SiC composites, the interphase between fiber and matrix is very important to improve the toughness [2] because the optimized interphase brings the deflection of cracks at the interphase, fiber pullout during the fracture, excellent interfacial shear strength and ductility between fiber and matrix which cause high mechanical properties. Among the various fabrication processes of SiC/SiC, the forced-flow/thermal gradient chemical vapor infiltration (FCVI) method is one of the best techniques to fabricate the SiC/SiC for fusion applications because this method produces a highly pure, stoichiometric, crystalline b-SiC matrix with low thermal stress which minimizes fiber damage during fabrication [6]. On the other hand, SiC matrix in SiC/SiC fabricated by the CVI method has low density and poor homogeneity, which cause the degradation of the mechanical and thermal properties. In this study, we carried out the optimization of this process to obtain higher and more homogeneity composite for the excellent mechan￾ical properties of SiC/SiC. We also studied the effects of the carbon and multilayer SiC/carbon interphase on the mech￾anical properties. 2. Experimental procedure We adopted two advanced SiC fiber fabrics as preforms: 2D-plain weave of Tyranno SA (Ube Industries, Ube, Japan). 0022-3697/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2004.06.030 Journal of Physics and Chemistry of Solids 66 (2005) 551–554 www.elsevier.com/locate/jpcs * Corresponding author. Tel.: C81 29 282 6099; fax: C81 29 284 3813. E-mail address: igawa@maico.tokai.jaeri.go.jp (N. Igawa)