Composites Science and Technology 69(2009)1623-1628 Contents lists available at ScienceDirect Composites Science and Technology ELSEVIER journalhomepagewww.elsevier.com/locate/compscitech High mechanical performance Sic/Sic composites by nite process with tailoring of appropriate fabrication temperature to fiber volume fraction Kazuya Shimoda, Akira Kohyama, Tatsuya Hinoki Institute of Advanced Energy, Kyoto University, Gokasho Uji, Kyoto 611-0011, Japar ARTICLE IN F O ABSTRACT Article history: Received 21 January 2009 (NITE)process, using pyrolytic carbon(PyC)-coated Tyranno-SA SiC fibers as reinforcement and Sic nano- Received in revised form 4 March 2009 powder with sintering additives for matrix formation. The effects of two kinds of fiber volume fraction Available online 24 March 2009 incorporating fabrication temperature were characterized on densification, microstructure and mechan- ical properties. Densification of the composites with low fiber volume fraction(appropriately 30 vol% eywords was developed even at lower fabrication temperature of 1800C, and then saturated at 3rd stage of matrix densification A Ceramic matrix composites(CMCs) esponding to classic liquid phase sintering. Hence, densification of the compo ites with high volume fraction (above 50 vol% became restricted because the many fibers retarded the B Mechanical properties nfiltration of Sic nano-powder at lower fabrication temperature of 1800C. when fabrication tempera B Stress/ strain curves ture increased by 1900C, densification of the composites was effectively enhanced in the intra-fiber E Sintering lltaneously the interaction between Pyc interface and matrix was strengthened. SEM observation on the fracture surface revealed that fiber pull-out length was accordingly changed with fab- rication temperature as well as fiber volume fraction, which dominated tensile fracture behaviors. Through NITE process, SiC/SiC composites with two fracture types were successfully developed by tailor- ing of appropriate fabrication temperature to fiber volume fraction as follows: (1)high ductility type and (2) high strength typ o 2009 Elsevier Ltd. All rights reserved. 1 Introduction cal properties under high temperature and neutron irradiation Advanced nuclear energy systems, such as gas cooled fast impregnation and pyrolysis(Pip)and melt infiltration(Mi)pro- reactor (GFR), very high temperature reactor(VHTR) and fusion cess are mainly adopted for the fabrication of Sic/Sic composites reactor are potential candidates for sustainable energy systems 5-7. However, still total performances of these composites are in the future. In order to realize these attractive energy systems, not satisfied for going of industrial stage. Matrix densification is structural materials must be responsible to keep their perfor- frequently emphasized as a key to improve poor thermo-mechan- mances under very severe environment including high tempera- ical properties in addition to gas tightness[8-10 The hot-press- ture and neutron irradiation. Today a major thrust is by the ing process is effective processing technique to offer the dense development of continuous fiber-reinforced ceramic matri omposites [11. Thermal stability and resistance against creep omposites(CFCCs)in general and continuous silicon carbide fi- of continuous Sic fiber as reinforcement are essential to fabricate ber-reinforced silicon carbide matrix( SiC/Sic)composites in par- SiC/SiC composites by hot-pressing. It has reported that Tyran ticular [1, 2. Because of continuous fiber-reinforcement, SiC/Sic no-SA fibers with high tensile strength and modulus show no composites are more damage tolerant to mechanical and thermal degradation in strength or change in composition on heating to loading( thermal shock) and have the capability for larger and or 1900C in an inert atmosphere and superior bend stress relaxa- complicated components than their SiC monolithic form. Also, in tion creep resistance to previous Sic-based fibers [12]. The devel- comparison to the best high-temperature metallic alloys, SiC/Sic opment of advanced Sic-based fibers with well-crystallized composites are lower specific gravity and thermal expansion, microstructure and near-stoichiometric composition, such as tyr- and have the potential for displaying excellent thermo-mechani- anno-SA fibers, made it possible to fabricate high-performance SiC/SiC composites even under harsh conditions by hot-pressing [13, 14. One of the novel accomplishments is a fabrication pro- uthor. Present address: DEN/DANS/DMN/SRMA, CEA-Sacl Essonne91191, france.Tel.:+33169082754:fax:+33169 cess for SiC/SiC composites, named nano-infiltration and transient 087167 eutectic-phase(NITE) process developed in our group at kyoto Ity 3538/s-see front matter o 2009 Elsevier Ltd. All right erved 016/j-compscitech. 2009.03.011High mechanical performance SiC/SiC composites by NITE process with tailoring of appropriate fabrication temperature to fiber volume fraction Kazuya Shimoda *, Akira Kohyama, Tatsuya Hinoki Institute of Advanced Energy, Kyoto University, Gokasho Uji, Kyoto 611-0011, Japan article info Article history: Received 21 January 2009 Received in revised form 4 March 2009 Accepted 11 March 2009 Available online 24 March 2009 Keywords: A. Ceramic matrix composites (CMCs) A. Nano particles B. Mechanical properties B. Stress/strain curves E. Sintering abstract Unidirectional SiC/SiC composites are prepared by nano-powder infiltration and transient eutectic-phase (NITE) process, using pyrolytic carbon (PyC)-coated Tyranno-SA SiC fibers as reinforcement and SiC nano￾powder with sintering additives for matrix formation. The effects of two kinds of fiber volume fraction incorporating fabrication temperature were characterized on densification, microstructure and mechan￾ical properties. Densification of the composites with low fiber volume fraction (appropriately 30 vol%) was developed even at lower fabrication temperature of 1800 C, and then saturated at 3rd stage of matrix densification corresponding to classic liquid phase sintering. Hence, densification of the compos￾ites with high volume fraction (above 50 vol%) became restricted because the many fibers retarded the infiltration of SiC nano-powder at lower fabrication temperature of 1800 C. When fabrication tempera￾ture increased by 1900 C, densification of the composites was effectively enhanced in the intra-fiber￾bundles and simultaneously the interaction between PyC interface and matrix was strengthened. SEM observation on the fracture surface revealed that fiber pull-out length was accordingly changed with fab￾rication temperature as well as fiber volume fraction, which dominated tensile fracture behaviors. Through NITE process, SiC/SiC composites with two fracture types were successfully developed by tailor￾ing of appropriate fabrication temperature to fiber volume fraction as follows: (1) high ductility type and (2) high strength type. 2009 Elsevier Ltd. All rights reserved. 1. Introduction Advanced nuclear energy systems, such as gas cooled fast reactor (GFR), very high temperature reactor (VHTR) and fusion reactor are potential candidates for sustainable energy systems in the future. In order to realize these attractive energy systems, structural materials must be responsible to keep their perfor￾mances under very severe environment including high tempera￾ture and neutron irradiation. Today a major thrust is by the development of continuous fiber-reinforced ceramic matrix composites (CFCCs) in general and continuous silicon carbide fi- ber-reinforced silicon carbide matrix (SiC/SiC) composites in par￾ticular [1,2]. Because of continuous fiber-reinforcement, SiC/SiC composites are more damage tolerant to mechanical and thermal loading (thermal shock) and have the capability for larger and/or complicated components than their SiC monolithic form. Also, in comparison to the best high-temperature metallic alloys, SiC/SiC composites are lower specific gravity and thermal expansion, and have the potential for displaying excellent thermo-mechani￾cal properties under high temperature and neutron irradiation [2–4]. Up to date, chemical vapor infiltration (CVI), polymer impregnation and pyrolysis (PIP) and melt infiltration (MI) pro￾cess are mainly adopted for the fabrication of SiC/SiC composites [5–7]. However, still total performances of these composites are not satisfied for going of industrial stage. Matrix densification is frequently emphasized as a key to improve poor thermo-mechan￾ical properties in addition to gas tightness [8–10]. The hot-press￾ing process is effective processing technique to offer the dense composites [11]. Thermal stability and resistance against creep of continuous SiC fiber as reinforcement are essential to fabricate SiC/SiC composites by hot-pressing. It has reported that Tyran￾noTM-SA fibers with high tensile strength and modulus show no degradation in strength or change in composition on heating to 1900 C in an inert atmosphere and superior bend stress relaxa￾tion creep resistance to previous SiC-based fibers [12]. The devel￾opment of advanced SiC-based fibers with well-crystallized microstructure and near-stoichiometric composition, such as Tyr￾annoTM-SA fibers, made it possible to fabricate high-performance SiC/SiC composites even under harsh conditions by hot-pressing [13,14]. One of the novel accomplishments is a fabrication pro￾cess for SiC/SiC composites, named nano-infiltration and transient eutectic-phase (NITE) process developed in our group at Kyoto University [8,9,13–17]. 0266-3538/$ - see front matter 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2009.03.011 * Corresponding author. Present address: DEN/DANS/DMN/SRMA, CEA-Saclay, Gif-sur-Yvette Cedex, Essonne 91191, France. Tel.: +33 1 69 08 27 54; fax: +33 1 69 08 71 67. E-mail address: kazuya.shimoda@cea.fr (K. Shimoda). Composites Science and Technology 69 (2009) 1623–1628 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech