Availableonlineatwww.sciencedirect.com COMPOSITES . ScienceDirect SCIENCE AND TECHNOLOGY ELSEVIER Composites Science and Technology 68(2008)98-105 w.elsevier. com/locate/compscitech Influence of pyrolytic carbon interface thickness on microstructure and mechanical properties of SiC/SiC composites by Nite process Kazuya Shimoda , Joon-Soo Park , Tatsuya Hinoki, Akira Kohyama Graduate School of Energy Science, Kyoto University, Institute of Energy Science and Technology Co. Ltd. Tokyo 101-0041 Japan Institute of Adranced Energy, Kyoto Unicersity, Gok Kyoto 611-0011 Received 25 October 2006: received in revised form 9 May 2007: accepted 16 May 2007 Available online 2 June 2007 Abstract Unidirectional SiC/SiC composites were prepared by Nano-Infiltration and Transient Eutectic-phase(NItE)process using Sic nano- powder infiltration technique, and the effects of pyrolytic carbon(Pyc) interface thickness between fibers and matrix on density, micro- structural evolution and mechanical properties were characterized. SiC fibers both with and without Pyc interface were employed as reinforcement and Sic nano-powder was employed for matrix formation with 12 mass% sintering additives of the total powder. The thickness of PyC layer deposited by chemical vapor deposition(CVD)process was highly-accurately controlled at about 0.25, 0.50 and 1.00 um. Nearly full-dense SiC/SiC composites with uncoated fibers caused strong interaction between fibers and matrix, resulting in a brittle fracture behavior without fiber pull-out. Higher strength with a pseudo-ductile fracture behavior could be obtained using 0.50 um of PyC interface thickness, where a lot of deflects and branches of the propagating cracks and fiber pull-out were observed. Induced PyC interface conditions strongly affect the density, microstructural evolution, and therefore dominate mechanical properties and fracture behaviors c 2007 Elsevier Ltd. All rights reserved Keywords: A. Ceramic-matrix composites( CMCs): B. Interface: B Stress/strain curves; E. Powder processing 1. Introduction high-crystallinity and near-stoichiometric composition in matrix have been recognized as key requirements for Continuous SiC fiber reinforced SiC matrix(SiC/SiC) high-temperature and neutron irradiation application [9 composites are promising structural candidates for 11]. From these aspects, a newly innovative process called advanced nuclear energy systems, such as gas cooled fast Nano-Infiltration and Transient Eutectic-phase (NITE reactor (GFR), very high temperature reactor (VhTR) process has been extensively developed in our group at and fusion reactor due to their potentiality for providing Kyoto University. NITE process, which is first successful excellent mechanical properties at high-temperature and application of liquid phase sintering(LPS) process to low induced radioactivity [1-4] matrix densification for SiC/SiC composites, enabled There have been many efforts to develop high-perfor- production of well-crystallized SiC matrix with low poros- mance SiC/SiC composites, using chemical vapor infiltra- ity by incorporating both SiC nano-powder infiltration and I), polymer infiltration and pyrolysis(PIP), the advanced SiC fibers with well-crystallized microstruc- reaction sintering/melting infiltration(RS/MI) and their ture and near-stoichiometric composition like TyrannoTM. combined processes [5-8]. However, the low porosity, SA fibers [12-16]. General properties advanced SiC/Sic are summarized in Table I Corresponding author. Tel +81 774 383465: fax: +81 774 383467 The role of interface/interphase in ceramic composites E-mail address: k-simd @iae. kyoto-uLac jp(K. Shimoda) is extremely important for structure applications. The 0266-3538/- see front matter e 2007 Elsevier Ltd. All rights reserved doi: 10.1016j. compscitech. 2007.05.037Influence of pyrolytic carbon interface thickness on microstructure and mechanical properties of SiC/SiC composites by NITE process Kazuya Shimoda a,*, Joon-Soo Park b,c, Tatsuya Hinoki c , Akira Kohyama c a Graduate School of Energy Science, Kyoto University, Gokasho Uji, Kyoto 611-0011, Japan b Institute of Energy Science and Technology Co. Ltd., Kanda, Tokyo 101-0041, Japan c Institute of Advanced Energy, Kyoto University, Gokasho Uji, Kyoto 611-0011, Japan Received 25 October 2006; received in revised form 9 May 2007; accepted 16 May 2007 Available online 2 June 2007 Abstract Unidirectional SiC/SiC composites were prepared by Nano-Infiltration and Transient Eutectic-phase (NITE) process using SiC nano￾powder infiltration technique, and the effects of pyrolytic carbon (PyC) interface thickness between fibers and matrix on density, micro￾structural evolution and mechanical properties were characterized. SiC fibers both with and without PyC interface were employed as reinforcement and SiC nano-powder was employed for matrix formation with 12 mass% sintering additives of the total powder. The thickness of PyC layer deposited by chemical vapor deposition (CVD) process was highly-accurately controlled at about 0.25, 0.50 and 1.00 lm. Nearly full-dense SiC/SiC composites with uncoated fibers caused strong interaction between fibers and matrix, resulting in a brittle fracture behavior without fiber pull-out. Higher strength with a pseudo-ductile fracture behavior could be obtained using 0.50 lm of PyC interface thickness, where a lot of deflects and branches of the propagating cracks and fiber pull-out were observed. Induced PyC interface conditions strongly affect the density, microstructural evolution, and therefore dominate mechanical properties and fracture behaviors. 2007 Elsevier Ltd. All rights reserved. Keywords: A. Ceramic-matrix composites (CMCs); B. Interface; B. Stress/strain curves; E. Powder processing 1. Introduction Continuous SiC fiber reinforced SiC matrix (SiC/SiC) composites are promising structural candidates for advanced nuclear energy systems, such as gas cooled fast reactor (GFR), very high temperature reactor (VHTR) and fusion reactor due to their potentiality for providing excellent mechanical properties at high-temperature and low induced radioactivity [1–4]. There have been many efforts to develop high-perfor￾mance SiC/SiC composites, using chemical vapor infiltra￾tion (CVI), polymer infiltration and pyrolysis (PIP), reaction sintering/melting infiltration (RS/MI) and their combined processes [5–8]. However, the low porosity, high-crystallinity and near-stoichiometric composition in matrix have been recognized as key requirements for high-temperature and neutron irradiation application [9– 11]. From these aspects, a newly innovative process called Nano-Infiltration and Transient Eutectic-phase (NITE) process has been extensively developed in our group at Kyoto University. NITE process, which is first successful application of liquid phase sintering (LPS) process to matrix densification for SiC/SiC composites, enabled a production of well-crystallized SiC matrix with low poros￾ity by incorporating both SiC nano-powder infiltration and the advanced SiC fibers with well-crystallized microstruc￾ture and near-stoichiometric composition like TyrannoTM￾SA fibers [12–16]. General properties and issues for advanced SiC/SiC are summarized in Table 1. The role of interface/interphase in ceramic composites is extremely important for structure applications. The 0266-3538/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2007.05.037 * Corresponding author. Tel.: +81 774 383465; fax: +81 774 383467. E-mail address: k-simd@iae.kyoto-u.ac.jp (K. Shimoda). www.elsevier.com/locate/compscitech Available online at www.sciencedirect.com Composites Science and Technology 68 (2008) 98–105 COMPOSITES SCIENCE AND TECHNOLOGY