CERAMICS 要 INTERNATIONAL ELSEVIER Ceramics International 31 (2005)525-53 Effects of Sic sub-layer on mechanical properties of Tyranno-SA/SIC composites with multiple interlayers Wen Yang", Hiroshi Araki, Akira Kohyama, Hiroshi Suzuki, Tetsuji Noda National Institute for materia INstitute of Advanced Energy, Kyoto University, Uj Received 30 April 2004; received in revised form 5 May 2004: accepted 28 June 2004 Available online 1 September 2004 Abstract Sic/SiC composites with single pyrolytic carbon(Py C) interlayer generally show significant strength degradations in oxidation/irradiation environments due to the poor oxidation/irradiation resistance of the PyC interlayer Incorporating SiC sub-layers in the Py C interlayer (SiC PyC)n multilayers has been proved effective on improving the oxidation/irradiation resistance of the materials. However, it remains uncle whether such stiff SiC sub-layer will cause decrease of the mechanical properties of a SiC/SiC composite, especially for newly developed advanced Tyranno-SA fibers reinforced one. In this study, two plain-woven Tyranno-SA/SiC composites with designed fiber/matrix interlayers of 100 nm PyC and 50 nm PyC 150 nm SiC +50 nm PyC, respectively, were fabricated to investigate the effects of the stiff SiC sub-layer on the mechanical properties. The results showed that the SiC sub-layer caused much higher interfacial shear strength (Iss) in the composite. However, the two composites exhibited a similar level of proportional limit stress and ultimate flexural strength. C 2004 Elsevier Ltd and Techna Group S.r. l. All rights reserved Keywords: B. Composites; C. Mechanical properties; D. SiC; Chemical vapor infiltration; PyC-SiC interlayers 1. Introduction by the fibers during the failure of the material. These energy dissipating mechanisms provide for improved apparent Ceramics possess many attractive properties for struc- fracture toughness and result in a non-catastrophic mode of tural and non-structural applications at elevated tem- failure. Carbon has been proved to be very effective peratures and under severe environments. Yet, limited interphase materials in CFCC [7]. SiC/SiC composites are mechanisms for stress concentration alleviation, and hence very attractive for applications at high-temperature harsh catastrophic fracture behavior, largely limited their applica- environments. They are also expected to be used as structure tions. The low fracture toughness of ceramics can be readily materials in advanced nuclear fusion/fission plants [8] improved by the incorporation of reinforcement fibers, However, SiC/Sic with carbon interlayer usually show whiskers, and particles, etc. [1-3]. For continuous ceramic significant degradation of performance when exposed to ber reinforced ceramic matrix( CFCC)composites, such as oxidation environment at elevated temperature [5] or under SiC fibers reinforced SiC matrix composites (SiC/SiC), neutron irradiation [9] because of serious degradation the fiber/matrix interface is critical on determining the damage of the carbon interlayer under these conditions performance of the materials [4-6]. A compliant interfacial Fortunately, it was found that when the carbon layer is thin yer(s) is necessary to produce modified reinforcement enou gh (less than 100 nm). the oxidation of the carbon ibers/matrix interfacial bonding in a CFCC to allow interphase could be limited due to a'self-healingbehavior interfacial debonding and matrix crack deflection/bridging 5]. Improving the oxidation and irradiation resistance requires thinner carbon interlayer, while deviation of matrix Corresponding author. Tel: +81 298 59 2842; fax: +81 298 59 2701. cracks needs sufficient thickness of the interphase [7]- E-mail address: yang wen nims go. jp(W. Yang Therefore, an alternating multilayer(PyC-SiC)n, with thin 0272-8842/S30.00@ 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved ramin2004.06.018Effects of SiC sub-layer on mechanical properties of Tyranno-SA/SiC composites with multiple interlayers Wen Yanga, *, Hiroshi Arakia , Akira Kohyamab , Hiroshi Suzukia , Tetsuji Nodaa a National Institute for Materials Science, Tsukuba 305-0047, Japan b Institute of Advanced Energy, Kyoto University, Uji 611-0011, Japan Received 30 April 2004; received in revised form 5 May 2004; accepted 28 June 2004 Available online 1 September 2004 Abstract SiC/SiC composites with single pyrolytic carbon (PyC) interlayer generally show significant strength degradations in oxidation/irradiation environments due to the poor oxidation/irradiation resistance of the PyC interlayer. Incorporating SiC sub-layers in the PyC interlayer (SiC￾PyC)n multilayers has been proved effective on improving the oxidation/irradiation resistance of the materials. However, it remains unclear whether such stiff SiC sub-layer will cause decrease of the mechanical properties of a SiC/SiC composite, especially for newly developed advanced Tyranno-SA fibers reinforced one. In this study, two plain-woven Tyranno-SA/SiC composites with designed fiber/matrix interlayers of 100 nm PyC and 50 nm PyC + 150 nm SiC + 50 nm PyC, respectively, were fabricated to investigate the effects of the stiff SiC sub-layer on the mechanical properties. The results showed that the SiC sub-layer caused much higher interfacial shear strength (ISS) in the composite. However, the two composites exhibited a similar level of proportional limit stress and ultimate flexural strength. # 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: B. Composites; C. Mechanical properties; D. SiC; Chemical vapor infiltration; PyC-SiC interlayers 1. Introduction Ceramics possess many attractive properties for struc￾tural and non-structural applications at elevated tem￾peratures and under severe environments. Yet, limited mechanisms for stress concentration alleviation, and hence catastrophic fracture behavior, largely limited their applica￾tions. The low fracture toughness of ceramics can be readily improved by the incorporation of reinforcement fibers, whiskers, and particles, etc. [1–3]. For continuous ceramic fiber reinforced ceramic matrix (CFCC) composites, such as SiC fibers reinforced SiC matrix composites (SiC/SiC), the fiber/matrix interface is critical on determining the performance of the materials [4–6]. A compliant interfacial layer(s) is necessary to produce modified reinforcement fibers/matrix interfacial bonding in a CFCC to allow interfacial debonding and matrix crack deflection/bridging by the fibers during the failure of the material. These energy￾dissipating mechanisms provide for improved apparent fracture toughness and result in a non-catastrophic mode of failure. Carbon has been proved to be very effective interphase materials in CFCC [7]. SiC/SiC composites are very attractive for applications at high-temperature harsh environments. They are also expected to be used as structure materials in advanced nuclear fusion/fission plants [8]. However, SiC/SiC with carbon interlayer usually show significant degradation of performance when exposed to oxidation environment at elevated temperature [5] or under neutron irradiation [9] because of serious degradation/ damage of the carbon interlayer under these conditions. Fortunately, it was found that when the carbon layer is thin enough (less than 100 nm), the oxidation of the carbon interphase could be limited due to a ‘self-healing’ behavior [5]. Improving the oxidation and irradiation resistance requires thinner carbon interlayer, while deviation of matrix cracks needs sufficient thickness of the interphase [7]. Therefore, an alternating multilayer (PyC-SiC)n, with thin www.elsevier.com/locate/ceramint Ceramics International 31 (2005) 525–531 * Corresponding author. Tel.: +81 298 59 2842; fax: +81 298 59 2701. E-mail address: yang.wen@nims.go.jp (W. Yang). 0272-8842/$30.00 # 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2004.06.018