journal of materials ELSEVIER Journal of Nuclear Materials 307-311(2002)1173-1177 www.elseviercom Effects of fibers and fabrication processes on mechanical properties of neutron irradiated SiC/SiC composites T Nozawa", T. Hinoki, Y. Katoh, A Kohyama Institute of Adranced Energy, Kyoto Unirersity, Gokasho, Uji, Kyoto 611-0011, Japan abstract Radiation effects on flexural properties of SiC/SiC composites fabricated by forced thermal gradient chemical vapor infiltration(F-CVI) process, reaction sintered (RS) process and polymer impregnation and pyrolysis(PIP)process were investigated. In this study, neutron irradiation at 1073 K up to 0. 4 x 102 n/m2(E>0.1 Mev) was performed. For F-CVI and RS SiC/SiC, due to the irradiation damage of interphase like pyrolytic carbon and boron nitride which were sensitive to neutron irradiation, composite stiffness was slightly decreased. On the contrary, for PIP SiC/SiC, there was lo significant change in stiffness before and after irradiation. Composite strength, however, was nearly stable against high-temperature irradiation with such a low fuence, except for Rs SiC/SiC, since mechanical characteristics of fiber and matrix themselves were still stable to neutron irradiation. However rs SiC/SiC had a slight reduction of flexural strength due to the severe degradation of the interface by neutron irradiation. C 2002 Elsevier Science B.v. All rights reserved 1. Introduction known to degrade due to the neutron irradiation >I displacement per atom(dpa)[4-7. This is because the Sic/SiC composites are attract partial detachment of fiber and matrix(F/M) interface structural applications, because occurred due to the degradation of Pyc by neutron ir and mechanical stability at high radiation and F/M interface partially lost load transfer function. Besides under neutron irradiation with much heat [1, 2), and others. In particular, recent improve- higher fluence, complete detachment of F/M interface ment of radiation stability has been achieved by the and hence large stress reduction occurred [8,9]. More- development of fabrication technique as well as by using over it was reported that shrinkage of amorphous fibers high-crystalline silicon carbide fibers with few impurities like Nicalon and Hi-Nicalon M fibers(Nippon Ca [34] bon Co. Ltd, Tokyo, Japan)and swelling of highly SiC/SiC composites fabricated by CVi process have crystalline P-Sic matrix produced irradiation-induce been conventionally used in irradiation researches be- internal stresses in the F/M interface [7]. by the presence cause of several advantages like high purity and high of these stresses, reduction of composite strength was crystallinity of their matrix. CVI derived SiC matrix enhanced. However this kind of stresses could be re- sites with pyrolytic carbon(PyC) interphase were. duced by using stoichiometric SiC fiber, such as Hi- Nicalon"M Type-S(Nippon Carbon Co. Ltd, Tokyo, Japan) or Tyranno SA (Ube Industries, Ltd, Ube, Japan). This is because both fiber and matrix swelled Corresponding author. Tel. +81-774 38 3463: fax: +81-774 in the same direction by neutron irradiation due to 383467 heir high-crystalline, near stoichiometric structure [10 E-mail address: nozawa(@iae. kyoto-u ac jp(T. Nozawa) On the while there is another advantage that severe 0022-3115/02/.see front matter 2002 Elsevier Science B v. All rights reserved PII:S0022-3115(02)Effects of fibers and fabrication processes on mechanical properties of neutron irradiated SiC/SiC composites T. Nozawa *, T. Hinoki, Y. Katoh, A. Kohyama Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan Abstract Radiation effects on flexural properties of SiC/SiC composites fabricated by forced thermal gradient chemical vapor infiltration (F-CVI) process, reaction sintered (RS) process and polymer impregnation and pyrolysis (PIP) process were investigated. In this study, neutron irradiation at 1073 K up to 0:4
1025 n/m2 (E > 0:1 MeV) was performed. For F-CVI and RS SiC/SiC, due to the irradiation damage of interphase like pyrolytic carbon and boron nitride, which were sensitive to neutron irradiation, composite stiffness was slightly decreased. On the contrary, for PIP SiC/SiC, there was no significant change in stiffness before and after irradiation. Composite strength, however, was nearly stable against high-temperature irradiation with such a low fluence, except for RS SiC/SiC, since mechanical characteristics of fiber and matrix themselves were still stable to neutron irradiation. However RS SiC/SiC had a slight reduction of flexural strength due to the severe degradation of the interface by neutron irradiation.
2002 Elsevier Science B.V. All rights reserved. 1. Introduction SiC/SiC composites are attractive materials for fusion structural applications, because of superior chemical and mechanical stability at high temperature, inherently possessed low induced-activation energy and after￾heat [1,2], and others. In particular, recent improve￾ment of radiation stability has been achieved by the development of fabrication technique as well as by using high-crystalline silicon carbide fibers with few impurities [3,4]. SiC/SiC composites fabricated by CVI process have been conventionally used in irradiation researches be￾cause of several advantages like high purity and high crystallinity of their matrix. CVI derived SiC matrix composites with pyrolytic carbon (PyC) interphase were known to degrade due to the neutron irradiation >1 displacement per atom (dpa) [4–7]. This is because the partial detachment of fiber and matrix (F/M) interface occurred due to the degradation of PyC by neutron ir￾radiation and F/M interface partially lost load transfer function. Besides under neutron irradiation with much higher fluence, complete detachment of F/M interface and hence large stress reduction occurred [8,9]. More￾over it was reported that shrinkage of amorphous fibers like NicalonTM and Hi-NicalonTM fibers (Nippon Car￾bon Co. Ltd., Tokyo, Japan) and swelling of highly crystalline b-SiC matrix produced irradiation-induced internal stresses in the F/M interface [7]. By the presence of these stresses, reduction of composite strength was enhanced. However this kind of stresses could be re￾duced by using stoichiometric SiC fiber, such as Hi￾NicalonTM Type-S (Nippon Carbon Co. Ltd., Tokyo, Japan) or TyrannoTM SA (Ube Industries, Ltd., Ube, Japan). This is because both fiber and matrix swelled in the same direction by neutron irradiation due to their high-crystalline, near stoichiometric structure [10]. On the while, there is another advantage that severe Journal of Nuclear Materials 307–311 (2002) 1173–1177 www.elsevier.com/locate/jnucmat * Corresponding author. Tel.: +81-774 38 3463; fax: +81-774 38 3467. E-mail address: tnozawa@iae.kyoto-u.ac.jp (T. Nozawa). 0022-3115/02/$ - see front matter
2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 1 1 5 ( 0 2 ) 0 1 0 5 7 - 7