Availableonlineatwww.sciencedirect.com al of DIRECTO nuciear materials ELSEVIER Journal of Nuclear Materials 329-333(2004)572-576 Fabrication of advanced Sic fiber/F-Cvi SiC matrix composites with Sic/C multi-layer interphase T. Taguchi . T Nozawa, N. Igawa, Y. Katoh, S Jitsukawa, A Kohyama b, T. Hinoki b,,LL.Snead Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan Institute of Aduanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan Metals and Ceramics Diuision, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, US.A Abstract Sic/SiC composite with Sic/C multi-layer interphase coated on advanced Sic fibers was fabricated by the forced thermal-gradient chemical vapor infiltration(F-CVI) process. SEM and tEM observations verified that Sic/c multi layer interphase was formed on SiC fibers. Both flexural and tensile strengths of Sic/Sic composite with Sic/C multi yer interphase were approximately l0% higher than composites fabricated with single carbon interphase. The SEM observation of fracture surface for the composite with Sic/C multi-layer interphase revealed cylindrical steps formed around the fiber. Apparently several crack deflections occurred within SiC/C multi-layer interphase. Moreover, the sicl C multi-layer applied in this study operated efficiently to improve the mechanical properties. c 2004 Elsevier B V. All rights reserved the fabrication of Sic/Sic composites because it yield highly crystalline, near-stoichiometoric SiC fiber dam- The continuous silicon carbide fiber reinforced sili- age during processing is minimized. The forced flow date materials for fusion reactors because of their improvement since the r. -CVD process is a further on carbide (SiC/SiC) composites are attractive candi- thermal-gradient CVI (F- ates of producing and high excellent mechanical properties at high temperature and porosity, which are the peculiar problem of CVi, are low induced radioactivity after neutron irradiation [ 1-3]. overcome 9]. Previous work by authors has reported on Recently, highly crystalline near-stoichiometric SiC fi F-CVI process optimization of Sic/Sic composite with bers have been produced including Tyranno SA [4]. carbon( C) interphase including the effect of interphase They have superior mechanical properties under irradi- thickness on tensile strength [10 ation and oxidation compared with their Sic-based It was reported that SiC/C multi-layer interphase predecessors. Various processes have been employed for advanced fiber composite fabrication including chemical mechanical properties compared to single C interphase apor infiltration (CVi), polymer impregnation and [12]. However, the effect of SiC/C multi-layer with the pyrolysis, reaction bonding and nano- infiltration and advanced SiC fiber on the composite tensile strengths transient eutectic-phase process [5-8. Among the vari- has not been reported. In this study, new concept(SiC ous fabrication processes, CVI is attractive process for C)x6 multi-layer interphase was applied with advanced Sic fibers for further improvement in mechanical properties. The first SiC layer is designed to strengthen Corresponding author. Tel. +81-29 282 6099: fax: +81-29 the bond between fiber and interphase. The second to 2825922. orth si are designed to provide multi-stage E-mail address: taguchi@ popsvr tokai jaeri. go. jp(T. Tagu- pull-out of The fifth and sixth Sic layers are de- multi-stage pull-out of fiber bundles 0022-3115/S- see front matter G 2004 Elsevier B.v. All rights reserved. doi: 10.1016/j-jntFabrication of advanced SiC fiber/F-CVI SiC matrix composites with SiC/C multi-layer interphase T. Taguchi a,*, T. Nozawa b , N. Igawa a , Y. Katoh c , S. Jitsukawa a , A. Kohyama b , T. Hinoki b,c, L.L. Snead c a Neutron Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan b Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan c Metals and Ceramics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, USA Abstract SiC/SiC composite with SiC/C multi-layer interphase coated on advanced SiC fibers was fabricated by the forced thermal-gradient chemical vapor infiltration (F-CVI) process. SEM and TEM observations verified that SiC/C multi￾layer interphase was formed on SiC fibers. Both flexural and tensile strengths of SiC/SiC composite with SiC/C multi￾layer interphase were approximately 10% higher than composites fabricated with single carbon interphase. The SEM observation of fracture surface for the composite with SiC/C multi-layer interphase revealed cylindrical steps formed around the fiber. Apparently several crack deflections occurred within SiC/C multi-layer interphase. Moreover, the SiC/ C multi-layer applied in this study operated efficiently to improve the mechanical properties.
2004 Elsevier B.V. All rights reserved. 1. Introduction The continuous silicon carbide fiber reinforced sili￾con carbide (SiC/SiC) composites are attractive candi￾date materials for fusion reactors because of their excellent mechanical properties at high temperature and low induced radioactivity after neutron irradiation [1–3]. Recently, highly crystalline near-stoichiometric SiC fi- bers have been produced includingTyranno SA [4]. They have superior mechanical properties under irradi￾ation and oxidation compared with their SiC-based predecessors. Various processes have been employed for advanced fiber composite fabrication includingchemical vapor infiltration (CVI), polymer impregnation and pyrolysis, reaction bondingand nano-infiltration and transient eutectic-phase process [5–8]. Amongthe vari￾ous fabrication processes, CVI is attractive process for the fabrication of SiC/SiC composites because it yields highly crystalline, near-stoichiometoric SiC fiber dam￾age during processing is minimized. The forced flow thermal-gradient CVI (F-CVI) process is a further improvement since the low rates of producingand high porosity, which are the peculiar problem of CVI, are overcome [9]. Previous work by authors has reported on F-CVI process optimization of SiC/SiC composite with carbon (C) interphase includingthe effect of interphase thickness on tensile strength [10,11]. It was reported that SiC/C multi-layer interphase composite with conventional fibers achieved superior mechanical properties compared to single C interphase [12]. However, the effect of SiC/C multi-layer with the advanced SiC fiber on the composite tensile strengths has not been reported. In this study, new concept (SiC/ C) · 6 multi-layer interphase was applied with advanced SiC fibers for further improvement in mechanical properties. The first SiC layer is designed to strengthen the bond between fiber and interphase. The second to fourth SiC layers are designed to provide multi-stage pull-out of fibers. The fifth and sixth SiC layers are de￾signed to provide multi-stage pull-out of fiber bundles. * Correspondingauthor. Tel.: +81-29 282 6099; fax: +81-29 282 5922. E-mail address: taguchi@popsvr.tokai.jaeri.go.jp (T. Tagu￾chi). 0022-3115/$ - see front matter
2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2004.04.120 www.elsevier.com/locate/jnucmat Journal of Nuclear Materials 329–333 (2004) 572–576