COMPOSITES SCIENCE AND TECHNOLOGY ELSEVIER Composites Science and Technology 61(2001)1323-1329 www.elsevier.com/locate/compscitech Improvement of the mechanical properties of hot-pressed silicon-carbide-fiber-reinforced silicon carbide composites by polycarbosilane impregnation Katsumi Yoshida,*, Masamitsu Imai, Toyohiko Yano Research Laboratory for Nuclear reactors, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8550, Japan Received 16 February 2001; accepted 18 February 2001 Abstract Green sheets of SiC with Al2OxY2O3-Cao sintering additives prepared by the doctor-blade method and polycarbosilane(PCs)- impregnated Hi-Nicalon cloth with a bN coating were used for the fabrication of Sic-fiber-reinforced Sic(Sic/SiCr)composites by hot-pressing. Two kinds of SiC/SiCr composites with different fiber volume fractions were fabricated and their room-temperature mechanical properties were investigated. These composites showed non-brittle fracture behavior. The maximum strength of a omposite with 52 vol. of fibers was about twice as high as that of a composite with 40 vol. of fibers, and the composite hot pressed at 1700 C showed the highest maximum strength. In this fabrication process, PCS-impregnation into Hi-Nicalon cloth was an effective way of forming the matrix between fibers. C 2001 Elsevier Science Ltd. All rights reserved Keywords: A Ceramic-matrix composites; A. Preceramic polymer; B Mechanical properties; Hot-pressing 1. Introduction speed, for example, in times of the order of a day by the forced CVI method [16]. In general, however, these pro- A composite consisting of silicon carbide reinforced cesses require long manufacturing times, resulting in high with continuous SiC fibers(SiC/SiCe) is one of the candi- processing cost. Furthermore, the composites fabricated date ceramic materials for high-temperature structural by these processes usually contain about 10-20 vol. of applications since SiC shows excellent high-temperature extended large voids, resulting in low mechanical and mechanical properties, high thermal conductivity and thermal properties. In order to simplify the fabrication good oxidation, corrosion and wear resistance [1, 2]. Fur- process and to obtain dense Sic/SiCr composites with thermore, Sic shows low activation on account of its high mechanical and thermal properties, the authors low atomic number and good resistance to high-energy have studied a fabrication process using hot-pressing. neutron irradiation and it is expected to be used as which offers the ability to fabricate dense composites structural material in future fusion reactors [3-14 [18-20 SiC/SiCr composite is mainly fabricated by chemical The present authors have reported that SiC/SiCr vapor infiltration( CVI) and polymer infiltration and composite was fabricated by using a green sheet of sic pyrolysis(PIP)methods [15-17. These processes have with Al2O3-Y2O3-Cao sintering additives and Sic some advantages such as high purity and low damage to slurry-impregnated two-dimensional(2D) plain-weave fibers as a consequence of the relatively low processing Hi-Nicalon cloth with and without a BN coating by temperature. There is a variety of CVi processes and hot-pressing at 1750C [19, 20]. Although the composites some of them can form the matrix with relatively high fabricated by this process achieved nearly full density they fractured in a brittle manner. It was considered hat the interfacial bonding between fiber and matrix Corresponding author. Tel : +81-3-5734-3082: fax: +81-3-5734- was too strong as a result of the reaction between the BN E-mail address: yoshida(@ nr titech ac jp(K. Yoshida). coating on the fiber and matrix components such as the Research Fellow of the Japan Society for the Promotion of sintering additives, and the fiber was degraded severely by exposure at a temperature as high as 1750C. Moreover, 0266-3538/01/S-see front matter C 2001 Elsevier Science Ltd. All rights reserved. PII:S0266-3538(01)00031-8Improvement of the mechanical properties of hot-pressed silicon-carbide-fiber-reinforced silicon carbide composites by polycarbosilane impregnation Katsumi Yoshida1,*, Masamitsu Imai, Toyohiko Yano Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8550, Japan Received 16 February 2001; accepted 18 February 2001 Abstract Green sheets of SiC with Al2O3–Y2O3–CaO sintering additives prepared by the doctor-blade method and polycarbosilane (PCS)- impregnated Hi-Nicalon cloth with a BN coating were used for the fabrication of SiC-fiber-reinforced SiC (SiC/SiCf) composites by hot-pressing. Two kinds of SiC/SiCf composites with different fiber volume fractions were fabricated and their room-temperature mechanical properties were investigated. These composites showed non-brittle fracture behavior. The maximum strength of a composite with 52 vol.% of fibers was about twice as high as that of a composite with 40 vol.% of fibers, and the composite hot￾pressed at 1700
C showed the highest maximum strength. In this fabrication process, PCS-impregnation into Hi-Nicalon cloth was an effective way of forming the matrix between fibers. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: A. Ceramic-matrix composites; A. Preceramic polymer; B. Mechanical properties; Hot-pressing 1. Introduction A composite consisting of silicon carbide reinforced with continuous SiC fibers (SiC/SiCf) is one of the candi￾date ceramic materials for high-temperature structural applications since SiC shows excellent high-temperature mechanical properties, high thermal conductivity and good oxidation, corrosion and wear resistance [1,2]. Fur￾thermore, SiC shows low activation on account of its low atomic number and good resistance to high-energy neutron irradiation and it is expected to be used as structural material in future fusion reactors [3–14]. SiC/SiCf composite is mainly fabricated by chemical vapor infiltration (CVI) and polymer infiltration and pyrolysis (PIP) methods [15–17]. These processes have some advantages such as high purity and low damage to fibers as a consequence of the relatively low processing temperature. There is a variety of CVI processes and some of them can form the matrix with relatively high speed, for example, in times of the order of a day by the forced CVI method [16]. In general, however, these pro￾cesses require long manufacturing times, resulting in high processing cost. Furthermore, the composites fabricated by these processes usually contain about 10–20 vol.% of extended large voids, resulting in low mechanical and thermal properties. In order to simplify the fabrication process and to obtain dense SiC/SiCf composites with high mechanical and thermal properties, the authors have studied a fabrication process using hot-pressing, which offers the ability to fabricate dense composites [18–20]. The present authors have reported that SiC/SiCf composite was fabricated by using a green sheet of SiC with Al2O3–Y2O3–CaO sintering additives and SiC slurry-impregnated two-dimensional (2D) plain-weave Hi-Nicalon cloth with and without a BN coating by hot-pressing at 1750
C [19,20]. Although the composites fabricated by this process achieved nearly full density, they fractured in a brittle manner. It was considered that the interfacial bonding between fiber and matrix was too strong as a result of the reaction between the BN coating on the fiber and matrix components such as the sintering additives, and the fiber was degraded severely by exposure at a temperature as high as 1750
C. Moreover, 0266-3538/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0266-3538(01)00031-8 Composites Science and Technology 61 (2001) 1323–1329 www.elsevier.com/locate/compscitech * Corresponding author. Tel.: +81-3-5734-3082; fax: +81-3-5734- 2959. E-mail address: yoshida@nr.titech.ac.jp (K. Yoshida). 1 Research Fellow of the Japan Society for the Promotion of Science