CERAMICS INTERNATIONAL SEVIER Ceramics International 31(2005)47-52 ETS-synthesized Hi-Nicalon fiber-SiC matrix composite Wen Yang , Hiroshi Araki, Akira Kohyama, Hiroshi Suzuki, Tetsuji Noda a National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan stitute of Advanced Energy, Kyoto University, CREST-ACE, Kyoto 611-0011, Japan Received 18 December 2003; received in revised form 6 February 2004; accepted 8 March 2004 Available online 26 June 2004 Abstract Tough ceramic matrix composites, such as SiC/SiC, require a compliant reinforcement/matrix interface he deposition of desired interface coatings on small diameter fibers in SiC/SiC composites is a substantial challenge and costly. w carbon-rich source gas ethyltrichlorosilane(ETS), was used to fabric SiC/SiC composite with eight harness satin-woven Hi-Nica bric cloth as reinforcement by the chemical vapor infiltration(CVi) process. a graphite fiber/matrix interlayer was spontaneously formed in the material from the ets during the CVI matrix densification process, resulting in the composite having a sound interfacial shear stress of 86 MPa. The composite nowed a high proportional limit stress of 450+65 MPa and an ultimate fexural strength of 567+ 75 MPa, coupled with ductile fracture behavior. This study indicates that the costly interfacial coating process might be omitted when ETs is used as source gas for SiC/SiC o2004 Elsevier Ltd and Techna S.r. l. All rights reserved Keywords: B. Composite; C Mechanical properties; D SiC; Chemical vapor infiltration; Ethyltrichlorosilane 1. Introduction of the materials, is closely dependent on the fiber/matrix in- terfacial shear/sliding strength. a weaker fiber/matrix bond- There has been a strong interest in ceramic matrix com- ing is prone to crack deflection at the interface while, in posites( CMC) for a variety of high-temperature, high-stress order to take advantages of the high strength of the compos applications in aerospace, hot engine and energy conversion ite fiber reinforcement, the interface must be strong enough [1-4 because the fracture tolerance of monolithic ceram- for effective load transfer between the fiber and the matrix ics can be readily improved by the incorporation of rein- Fortunately, this interfacial shear/sliding strength can be ad- forcements fibers, whiskers, and/or particles. The reinforce- justed to the required range through the deposition of a com- ment/matrix interphase plays a critical role against catas- pliant fiber/matrix interfacial coating layer(s)[6-91 trophic failure for the CMC, especially for continuous fiber A compliant interlayer is necessary for tough SiC/SiC reinforced ceramic matrix composites(CFCC). In a CFCC, composites Carbon remains the most effective interphase a transverse matrix crack can be deflected with is- material [10, 11]. However, the deposition of desired inter- sipation occurring via several mechanisms as addressed by face coatings on small diameter fibers has proved to be a Besmann et al. [5] debonding at the fiber/matrix interface, substantial challenge for a variety of processes including So- crack deflection, crack bridging by the fibers, fiber sliding, lution, sol-gel, and chemical vapor deposition [5] and eventual fiber fracture. These energy-dissipating mecha- nisms provide for improved apparent fracture toughness and result in a non-catastrophic mode of failure. Obviously, the gas, methyltrichlorosilane(MTS, CH3 SiCl3) that contains performance of these mechanisms, and thus the performance equal carbon and silicon atoms, to fabricate a Sic/Sic com- posite with automatic graphite interfacial layer formation author.Tel:+81-298-59-2739 The interlayer structures, interfacial shear strength (ISs) fax:+81 2701 and mechanical properties of the material under three-point ss:yang wen @nims. go. jp(w. Yang) 0272-8842/S30.00@ 2004 Elsevier Ltd and Techna S.r. I. All rights reserved doi:10.1016/ ceramist2004.03.033Ceramics International 31 (2005) 47–52 ETS-synthesized Hi-Nicalon fiber–SiC matrix composite Wen Yang a,∗, Hiroshi Araki a, Akira Kohyama b, Hiroshi Suzuki a, Tetsuji Noda a a National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan b Institute of Advanced Energy, Kyoto University, CREST-ACE, Kyoto 611-0011, Japan Received 18 December 2003; received in revised form 6 February 2004; accepted 8 March 2004 Available online 26 June 2004 Abstract Tough ceramic matrix composites, such as SiC/SiC, require a compliant reinforcement/matrix interface coating. The deposition of desired interface coatings on small diameter fibers in SiC/SiC composites is a substantial challenge and costly. A new carbon-rich source gas, ethyltrichlorosilane (ETS), was used to fabric SiC/SiC composite with eight harness satin-woven Hi-Nicalon fabric cloth as reinforcement by the chemical vapor infiltration (CVI) process. A graphite fiber/matrix interlayer was spontaneously formed in the material from the ETS during the CVI matrix densification process, resulting in the composite having a sound interfacial shear stress of 86 MPa. The composite showed a high proportional limit stress of 450 ± 65 MPa and an ultimate flexural strength of 567 ± 75 MPa, coupled with ductile fracture behavior. This study indicates that the costly interfacial coating process might be omitted when ETS is used as source gas for SiC/SiC composite. © 2004 Elsevier Ltd and Techna S.r.l. All rights reserved. Keywords: B. Composite; C. Mechanical properties; D. SiC; Chemical vapor infiltration; Ethyltrichlorosilane 1. Introduction There has been a strong interest in ceramic matrix com￾posites (CMC) for a variety of high-temperature, high-stress applications in aerospace, hot engine and energy conversion [1–4] because the fracture tolerance of monolithic ceram￾ics can be readily improved by the incorporation of rein￾forcements fibers, whiskers, and/or particles. The reinforce￾ment/matrix interphase plays a critical role against catas￾trophic failure for the CMC, especially for continuous fiber reinforced ceramic matrix composites (CFCC). In a CFCC, a transverse matrix crack can be deflected with energy dis￾sipation occurring via several mechanisms as addressed by Besmann et al. [5]: debonding at the fiber/matrix interface, crack deflection, crack bridging by the fibers, fiber sliding, and eventual fiber fracture. These energy–dissipating mecha￾nisms provide for improved apparent fracture toughness and result in a non-catastrophic mode of failure. Obviously, the performance of these mechanisms, and thus the performance ∗ Corresponding author. Tel.: +81-298-59-2739; fax: +81-298-59-2701. E-mail address: yang.wen@nims.go.jp (W. Yang). of the materials, is closely dependent on the fiber/matrix in￾terfacial shear/sliding strength. A weaker fiber/matrix bond￾ing is prone to crack deflection at the interface while, in order to take advantages of the high strength of the compos￾ite fiber reinforcement, the interface must be strong enough for effective load transfer between the fiber and the matrix. Fortunately, this interfacial shear/sliding strength can be ad￾justed to the required range through the deposition of a com￾pliant fiber/matrix interfacial coating layer(s) [6–9]. A compliant interlayer is necessary for tough SiC/SiC composites. Carbon remains the most effective interphase material [10,11]. However, the deposition of desired inter￾face coatings on small diameter fibers has proved to be a substantial challenge for a variety of processes including so￾lution, sol–gel, and chemical vapor deposition [5]. In this study, a new carbon-rich source gas, ETS (C2H5SiCl3), was used rather than the more widely used gas, methyltrichlorosilane (MTS, CH3SiCl3) that contains equal carbon and silicon atoms, to fabricate a SiC/SiC com￾posite with automatic graphite interfacial layer formation. The interlayer structures, interfacial shear strength (ISS) and mechanical properties of the material under three-point bending were investigated. 0272-8842/$30.00 © 2004 Elsevier Ltd and Techna S.r.l. All rights reserved. doi:10.1016/j.ceramint.2004.03.033