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 afterheat [1,2], and others. In particular, recent improvement 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 because 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 irradiation 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]. Moreover it was reported that shrinkage of amorphous fibers like NicalonTM and Hi-NicalonTM fibers (Nippon Carbon 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 reduced by using stoichiometric SiC fiber, such as HiNicalonTM 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
l174 T. Nozawa et al. /Journal of Nuclear Materials 307-311(2002)1173-1177 degradation of stoichiometric fibers themselves does not a100 occur after neutron irradiation up to 10 dpa [8, 9]. 8 Consequently, the composite structure and strength be- E came more stable against neutron exposure. However, there are few studies on the stability of Sic/Sic against neutron exposure, especially far fuences 0.1 Mev) at irradiation [13, 14. In this experiment, volume changes 1073 K. In this study, this fluence corresponds to 0. 4 dpa of each F-CVI SiC/SiC were less than 0.6%. High crys- (1dpa=1×1035n/m2) talline SiC fibers like Hi-NicalonM Type-s, Tyranno SA Table I Test materials CS02 CHOI POL Matrix F-CVI SIC FCVI SIC FCVI SiC RS SIC PIP SIC Fiber Hi-Nicalon Type-s Tyranno-SA Hi-Nicalon Hi-Nicalon Crystal ure of fiber Crystal ro crystal Micro crystal P/W P/W P/W Pyc Py Gradient C Thickness of interphase(nm) 150 150 l50 Density (Mg/m) 2.82 2.11 ORNL ORN ORNL Toshiba Ube
degradation of stoichiometric fibers themselves does not occur after neutron irradiation up to 10 dpa [8,9]. Consequently, the composite structure and strength became more stable against neutron exposure. However, there are few studies on the stability of SiC/SiC against neutron exposure, especially far fluences 0:1 MeV) at 1073 K. In this study, this fluence corresponds to 0.4 dpa (1 dpa ¼ 1 1025 n/m2). Mechanical stabilities against neutron irradiation were evaluated by 3-point flexural tests. Support span of test beam was 18.0 mm. All the tests were conducted by using an electromechanical testing machine at room temperature with the crosshead control of 3:0 105 m/s, on the basis of ASTM C1341 [12]. Micro-structural observations were also conducted by using scanning electron microscopy (SEM) after mechanical tests. 3. Results and discussion 3.1. Neutron effect on F-CVI SiC/SiC Significant reduction of flexural strength did not occur and flexural strength was quite stable for all FCVI derived composites regardless of the fiber types as shown in Figs. 2 and 3. This is because dimensional changes in fiber and matrix might be quite small up to 0.4 dpa in neutron dose and also the strength of each component was still stable under such a low fluence irradiation [13,14]. In this experiment, volume changes of each F-CVI SiC/SiC were less than 0.6%. High crystalline SiC fibers like Hi-NicalonTM Type-S, Tyranno SA Fig. 1. Compositionally gradient SiC–C interphase. Table 1 Test materials CS01 CS02 CH01 RH01 PN01 Matrix F-CVI SiC F-CVI SiC F-CVI SiC RS SiC PIP SiC Fiber Hi-Nicalon Type-S Tyranno-SA Hi-Nicalon Hi-Nicalon Tyranno-TE Crystal structure of fiber Crystal Crystal Micro crystal Micro crystal Amorphous Architecture S/W P/W P/W UD P/W Interphase PyC PyC PyC BN Gradient C Thickness of interphase (nm) 150 150 150 – 200 Density (Mg/m3) 2.22 2.26 2.38 2.82 2.11 Supplier ORNL ORNL ORNL Toshiba Ube 1174 T. Nozawa et al. / Journal of Nuclear Materials 307–311 (2002) 1173–1177
T. Nozawa et al. Journal of Nuclear Materials 307-311(2002)1173-1177 fibers and B-Sic as matrix swells due to the lattice ex- diminished easily because of their high mobility. Con pansion by the accumulation of radiation-induced point sequently the radiation effect was slightly limited. On the defects.However at higher temperature, most of them contrary, Hi-Nicalon"M fibers are known to shrink and to increase their strength slightly by densification. How ever fiber shrinkage was also hard to occur in such a low 500 dose and high temperature irradiation for the same Neutron irradiation: 1073K, -0 4 dpa(at JMTR) eason. Similarly, proportional limit stress of all F-CVI 40 CHOI Sic/SiC was not also changed against the irradiation up CSOl to 0. 4 dpa because of good stabilities of fiber and matrix. 300 CS02 However reduction of elastic modulus of f-cvi sic Sic cannot be ignored. According to Osborne et al, the elastic modulus of B-Sic composing matrix and high crystalline Sic fibers has severe degradation against 100 Non-Irrad. Irac neutron irradiation at about 773 K up to about 0.5 dpa [5]. This degradation of stiffness was attributed to lat- Non-Irrad tice expansion of high-crystalline SiC caused by swelling mensional changes of fiber and matrix considered Displacement[mm] to be quite small in the irradiation at higher tempera tures like this experiment. From this reason, reduction Fig. 2. Stress-displacement relationships of irradiated and non- of composite stiffness seems mainly due to another irradiated F-CVI SiC/SiC composites mechanism. Possibly, degradation of F/M interface re- although the were no visible differences in fracture behaviors before 口 Elastic modulus口on% Yield Stress口 lexural strength and after neutron irradiation(Figs. 4 and 5). The F/M interface lost its load transferring function due to the degradation of PyC, which is sensitive to radiation [16]. even at low dose neutron irradiation 3. 2. Neutron effect on RS SiC/SiC Hi-NicalonTM fiber reinforced rs derived Sic matri composite with bn interphase was damaged by neutron irradiation up to 0.4 dpa(Figs. 6 and 7). All mechanical characteristics such as flexural strength, elastic modulus HNL-S/PyC/FCVI-SiC TySA/PyC/FCVI-SiC HNUPyCFCVI-Sic and proportional limit stress tended to decrease after eutron irradiation Fig. 3. Neutron irradiation effect on flexural properties of Similar to F-Cvi derived SiC matrix, rs derived Sic F-CVI SiC/SiC composites. matrix is, in general, highly crystalline. Hence, it is Cso Cso2 CHO1 RHO1 Fig. 4. Fracture appearances of non-irradiated F-CVl, RS and PIP SiC/SiC composites
fibers and b-SiC as matrix swells due to the lattice expansion by the accumulation of radiation-induced point defects. However at higher temperature, most of them diminished easily because of their high mobility. Consequently the radiation effect was slightly limited. On the contrary, Hi-NicalonTM fibers are known to shrink and to increase their strength slightly by densification. However fiber shrinkage was also hard to occur in such a low dose and high temperature irradiation for the same reason. Similarly, proportional limit stress of all F-CVI SiC/SiC was not also changed against the irradiation up to 0.4 dpa because of good stabilities of fiber and matrix. However reduction of elastic modulus of F-CVI SiC/ SiC cannot be ignored. According to Osborne et al., the elastic modulus of b-SiC composing matrix and highcrystalline SiC fibers has severe degradation against neutron irradiation at about 773 K up to about 0.5 dpa [15]. This degradation of stiffness was attributed to lattice expansion of high-crystalline SiC caused by swelling. However, as mentioned previously, influences of dimensional changes of fiber and matrix were considered to be quite small in the irradiation at higher temperatures like this experiment. From this reason, reduction of composite stiffness seems mainly due to another mechanism. Possibly, degradation of F/M interface resulted in a decreasing composite stiffness, although there were no visible differences in fracture behaviors before and after neutron irradiation (Figs. 4 and 5). The F/M interface lost its load transferring function due to the degradation of PyC, which is sensitive to radiation [16], even at low dose neutron irradiation. 3.2. Neutron effect on RS SiC/SiC Hi-NicalonTM fiber reinforced RS derived SiC matrix composite with BN interphase was damaged by neutron irradiation up to 0.4 dpa (Figs. 6 and 7). All mechanical characteristics such as flexural strength, elastic modulus and proportional limit stress tended to decrease after neutron irradiation. Similar to F-CVI derived SiC matrix, RS derived SiC matrix is, in general, highly crystalline. Hence, it is 0 100 200 300 400 500 0 0.5 1 1.5 2 Displacement [mm] Flexure Stress [MPa] Irrad. Irrad. Irrad. Non-Irrad. Non-Irrad. Non-Irrad. CS01 CS02 CH01 Neutron irradiation: 1073K, ~0.4 dpa (at JMTR) Fig. 2. Stress–displacement relationships of irradiated and nonirradiated F-CVI SiC/SiC composites. 0 0.5 1 1.5 HNL-S/PyC/FCVI-SiC (CS01) TySA/PyC/FCVI-SiC (CS02) HNL/PyC/FCVI-SiC (CH01) Irrad./Unirrad. Elastic Modulus 0.01% Yield Stress Flexural Strength Fig. 3. Neutron irradiation effect on flexural properties of F-CVI SiC/SiC composites. Fig. 4. Fracture appearances of non-irradiated F-CVI, RS and PIP SiC/SiC composites. T. Nozawa et al. / Journal of Nuclear Materials 307–311 (2002) 1173–1177 1175
T. Nozawa et al. / Journal of Nuclear Materials 307-311(2002 )1173-1177 Cs01 Cso2 CHO1 RHO1 N01 Fig. 5. Fracture appearances of irradiated F-CVl, RS and PIP SiC/SiC composites 00 ties of undesired excess carbon and boron in the matrix Neutron irradiation: 1073K, -0.4 dpa(at JMTR) These impurities might be induced during processing 400 They are known to be one of the most sensitive elements to neutron irradiation. Although helium production from boron by neutron irradiation was not identified in 0 his study, it cannot be excluded. In this case, neutron PNO damage of these impurities might result in a decreased matrix strength. Further investigations are necessary to Non-rr discuss this 100 Reduction of the elastic modulus can also be lained as follows. Obviously, non-irradiated composite failed just after the matrix cracking stress(Fig. 6). Also there were short pullouts of fibers at the fracture surface (Fig. 4). This means that the interfacial function to de- fect cracks and to transfer load between fiber and ma- Fig. 6. Stress-displacement relationships of irradiated and non- trix has nearly been lost before irradiation because irradiated RS and PIP SiC/SiC composites. cracks originating from the matrix penetrated into fibers due to the strong bonding between fiber and matrix. However, the BN interphase, was expected to be de- DElastic Modulus [0.01% Yield Stress I Flexural Strength graded by neutron irradiation and the F/M interface became much weaker after neutron irradiation. Spatial etween fiber and atachment of fiber and interphase, were defected frequently(Fig. 5) Hence the composite modulus decreased since the de- flection of composite increased. 3.3. Neutron effect on PlP Sic/siC There were no significant changes in flexural prop- erties of Tyranno M TE fiber reinforced PIP derived SiC HNL/BN/RS-SiC matrix composite before and after neutron irradiation S6-C/PIP-SIC up to 0.4 dpa(Figs. 6 and 7). This is explained by no significant structural and physical change of fiber, ma- Fig. 7. Neutron irradiation effect on flexural properties of Rs trix and also good performance of F/M interface before d PIP SiC/SiC composites. and after neutron irradiation TyrannoM-TE, which had an amorphous structure natural that matrix was stable and independent of like e Nicalon"M fiber, might be non-sensitive to neutron composite strength reduction by irradiation. However, it irradiation up to 0. 4 dpa, according to the stability of was revealed that this material contained small quanti- Nicalon against low fluence neutron. Similarly it is
natural that matrix was stable and independent of composite strength reduction by irradiation. However, it was revealed that this material contained small quantities of undesired excess carbon and boron in the matrix. These impurities might be induced during processing. They are known to be one of the most sensitive elements to neutron irradiation. Although helium production from boron by neutron irradiation was not identified in this study, it cannot be excluded. In this case, neutron damage of these impurities might result in a decreased matrix strength. Further investigations are necessary to discuss this. Reduction of the elastic modulus can also be explained as follows. Obviously, non-irradiated composite failed just after the matrix cracking stress (Fig. 6). Also there were short pullouts of fibers at the fracture surface (Fig. 4). This means that the interfacial function to de- flect cracks and to transfer load between fiber and matrix has nearly been lost before irradiation because cracks originating from the matrix penetrated into fibers due to the strong bonding between fiber and matrix. However, the BN interphase, was expected to be degraded by neutron irradiation and the F/M interface became much weaker after neutron irradiation. Spatial gaps between fiber and interphase, i.e. detachment of fiber and interphase, were defected frequently (Fig. 5). Hence the composite modulus decreased since the de- flection of composite increased. 3.3. Neutron effect on PIP SiC/SiC There were no significant changes in flexural properties of TyrannoTM TE fiber reinforced PIP derived SiC matrix composite before and after neutron irradiation up to 0.4 dpa (Figs. 6 and 7). This is explained by no significant structural and physical change of fiber, matrix and also good performance of F/M interface before and after neutron irradiation. TyrannoTM-TE, which had an amorphous structure like NicalonTM fiber, might be non-sensitive to neutron irradiation up to 0.4 dpa, according to the stability of NicalonTM against low fluence neutron. Similarly it is Fig. 5. Fracture appearances of irradiated F-CVI, RS and PIP SiC/SiC composites. Irrad. Non-Irrad. RH01 PN01 Irrad. Non-Irrad. 0 100 200 300 400 500 0 0.5 1 1.5 Displacement [mm] Flexure Stress [MPa] Neutron irradiation: 1073K, ~0.4 dpa (at JMTR) Fig. 6. Stress–displacement relationships of irradiated and nonirradiated RS and PIP SiC/SiC composites. 0 0.5 1 1.5 HNL/BN/RS-SiC (RH01) TyTE/S6-C/PIP-SiC (PN01) Irrad./Unirrad. Elastic Modulus 0.01% Yield Stress Flexural Strength Fig. 7. Neutron irradiation effect on flexural properties of RS and PIP SiC/SiC composites. 1176 T. Nozawa et al. / Journal of Nuclear Materials 307–311 (2002) 1173–1177
T. Nozawa et al. Journal of Nuclear Materials 307-311(2002)1173-1177 possible that PlP derived Sic matrix with low crystalline Acknowledgements structure showed little radiation effects. In short. com- bination of both polymer-derived fiber and matrix might The authors would like to express their have minimized the influence of irradiation-induced preciation to Dr Snead at Oak Ridge National Labo- volume change. In addition to these facts, it can also be ratory, Dr Suyama at Toshiba Co Ltd, and Dr Sato at concluded that compositionally degraded Sic-C inter- Ube Industries for material supplies and Professor phase(Fig. 1) might be effective for radiation-resistant Narui at Tohoku Ur composites, for the explanation of the good resistance of was performed as a part of collaboration at Japan-US PIP SiC/Sic st neutron irradiation. However, Program for Irradiation Test of Fusion Materials (JU slight increase in flexural modulus occurred likely due to PITER) and Core Research for Evolutional Science and the partial crystallization of polymer-derived amor- Technology(CREST) program hous Sic matrix and fibers. Otherwise, significant matrix defects like pre-existing pores and cracks might have masked irradiation-induced changes. References [R H. Jones, LL. Snead, A Kohyama, P Fenici, Fus. Eng 4. Conclusions Des.41(1998)15 2L. L. Snead, R H. Jones, A. Kohyama, P. Fenici, J. Nucl Radiation effects on flexural properties of F-CVI, RS Mater.233-237(1996)23 and PIP SiC/SiC were investigated. This experiment was BY. Katoh, M. Kotani, H. Kishimoto, w. Yang, A characteristic in neutron irradiation at low doses up to Kohyama, J Nucl. Mater. 289(2001)42 0.4 dpa at high-temperature, 1073 K. Main conclusions 4L. L. Snead, Y. Katoh, A. Kohyama, J. L. Bailey, N L. were summarized as follows Vaughn, R.A. Lowden, J. Nucl. Mater. 283-287(2000) There were few influences of fibers and matrices on flexural properties of Sic/Sic against the neutron irra- [AJ Frias Robelo, H.W. Scholz, H. Kolbe, G.P. Tartaga- diation up to 0.4 dpa at 1073 K. Fiber and matrix lia, P. Fenici, J. Nucl. Mater. 263(1998)1582 6L. L. Snead, M.C. Osborne, R.A. Lowden, J. Strizak, RJ themselves did not degrade significantly by neutron ir Shinavski, K.L. More, W.S.Eatherly, J. Bailey, A M radiation at such low fluences. On the contrary, F/M Williams, J Nucl. Mater. 253(1998)20 interface was significantly damaged by irradiation up to [7G.w. Hollenberg. C H. Henager Jr, G.E. Youngblood, 0. 4 dpa which resulted in the decrease of the composite D.J. Trimble, S.A. Simonson, G.A. Newsome, E. Lewis, J strength, especially of the modulus of elasticity Nucl. Mater. 219(1995)70 8 M.C. Osborne, C.R. Hubbard, L L. Snead, D. Steiner, J F-CVI SiC/SiC showed a slight decrease in the elastic Nud. Mater.253(1998)67 modulus due to enlarged deflection by the degrada [9]GE. Youngblood, R.H. Jones, A Kohyama, LL. Snead, tion of Pyc interphase. However the composite J.Nucl. Mater.258-263(1998)1551 strength was still stable due to the dimensional and [10]LL. Snead, S.J. Zinkle, J.C. Hay, M.C. Osborne, Nucl. and Meth. B 141(1998)123. mechanical stability of fiber and matrix against neu- cawa. K. Bansaku N. Watanabe. Y. Nomura. M tron irradiation s.Sci. Technol. 58(1998)51 2. Composite strength and stiffness of rs SiC/SiC were [12] C1341 Flexural Properties of Continuous Fiber-Reinforced degraded by radiation damages of the bn interphase Advanced Ceramic Composites, in: Annual Book of 3. PiP SiC/Sic was stable against neutron irradiation ASTM Standards, ASTM, Conshohocken, PA, 1998, P. up to 0. 4 dpa because no significant degradation of [13]RJ. Price, J Nucl. Mater. 33(1969)17 after irradiation. Amorphous SiC fiber and matrix [14R.. Price, G.R. Hopkins, J Nucl. Mater. 108&109(1982) 732. did not degrade their flexural properties after neutron irradiation up to 0.4 dpa. Also compositionally de [15 M.C. Osborne, J C. Hay, LL. Snead, D. Steiner, J.Am. Ceram.Soc.82(1999)2490. graded Sic-C interface might be very effective for [16JHW. Simmons, Radiation Damage in Graphite, Inter- neutron irradiation and it is considered to be a pror national Series of Monographs in Nuclear Energy, vol. ising interface option for SiC/SiC composites 102. 1965. Pergamon
possible that PIP derived SiC matrix with low crystalline structure showed little radiation effects. In short, combination of both polymer-derived fiber and matrix might have minimized the influence of irradiation-induced volume change. In addition to these facts, it can also be concluded that compositionally degraded SiC–C interphase (Fig. 1) might be effective for radiation-resistant composites, for the explanation of the good resistance of PIP SiC/SiC against neutron irradiation. However, slight increase in flexural modulus occurred likely due to the partial crystallization of polymer-derived amorphous SiC matrix and fibers. Otherwise, significant matrix defects like pre-existing pores and cracks might have masked irradiation-induced changes. 4. Conclusions Radiation effects on flexural properties of F-CVI, RS and PIP SiC/SiC were investigated. This experiment was characteristic in neutron irradiation at low doses up to 0.4 dpa at high-temperature, 1073 K. Main conclusions were summarized as follows. There were few influences of fibers and matrices on flexural properties of SiC/SiC against the neutron irradiation up to 0.4 dpa at 1073 K. Fiber and matrix themselves did not degrade significantly by neutron irradiation at such low fluences. On the contrary, F/M interface was significantly damaged by irradiation up to 0.4 dpa which resulted in the decrease of the composite strength, especially of the modulus of elasticity. 1. F-CVI SiC/SiC showed a slight decrease in the elastic modulus due to enlarged deflection by the degradation of PyC interphase. However the composite strength was still stable due to the dimensional and mechanical stability of fiber and matrix against neutron irradiation. 2. Composite strength and stiffness of RS SiC/SiC were degraded by radiation damages of the BN interphase. 3. PIP SiC/SiC was stable against neutron irradiation up to 0.4 dpa because no significant degradation of fiber, matrix and F/M interface occurred before and after irradiation. Amorphous SiC fiber and matrix did not degrade their flexural properties after neutron irradiation up to 0.4 dpa. Also compositionally degraded SiC–C interface might be very effective for neutron irradiation and it is considered to be a promising interface option for SiC/SiC composites. Acknowledgements The authors would like to express their sincere appreciation to Dr Snead at OakRidge National Laboratory, Dr Suyama at Toshiba Co. Ltd., and Dr Sato at Ube Industries for material supplies and Professor Narui at Tohoku University for irradiation. This work was performed as a part of collaboration at Japan–US Program for Irradiation Test of Fusion Materials (JUPITER) and Core Research for Evolutional Science and Technology (CREST) program. References [1] R.H. Jones, L.L. Snead, A. Kohyama, P. Fenici, Fus. Eng. Des. 41 (1998) 15. [2] L.L. Snead, R.H. Jones, A. Kohyama, P. Fenici, J. Nucl. Mater. 233–237 (1996) 23. [3] Y. Katoh, M. Kotani, H. Kishimoto, W. Yang, A. Kohyama, J. Nucl. Mater. 289 (2001) 42. [4] L.L. Snead, Y. Katoh, A. Kohyama, J.L. Bailey, N.L. Vaughm, R.A. Lowden, J. Nucl. Mater. 283–287 (2000) 551. [5] A.J. Frias Robelo, H.W. Scholz, H. Kolbe, G.P. Tartagalia, P. Fenici, J. Nucl. Mater. 263 (1998) 1582. [6] L.L. Snead, M.C. Osborne, R.A. Lowden, J. Strizak, R.J. Shinavski, K.L. More, W.S. Eatherly, J. Bailey, A.M. Williams, J. Nucl. Mater. 253 (1998) 20. [7] G.W. Hollenberg, C.H. Henager Jr., G.E. Youngblood, D.J. Trimble, S.A. Simonson, G.A. Newsome, E. Lewis, J. Nucl. Mater. 219 (1995) 70. [8] M.C. Osborne, C.R. Hubbard, L.L. Snead, D. Steiner, J. Nucl. Mater. 253 (1998) 67. [9] G.E. Youngblood, R.H. Jones, A. Kohyama, L.L. Snead, J. Nucl. Mater. 258–263 (1998) 1551. [10] L.L. Snead, S.J. Zinkle, J.C. Hay, M.C. Osborne, Nucl. Instrum. and Meth. B 141 (1998) 123. [11] T. Ishikawa, K. Bansaku, N. Watanabe, Y. Nomura, M. Shibuya, T. Hirokawa, Compos. Sci. Technol. 58 (1998) 51. [12] C1341 Flexural Properties of Continuous Fiber-Reinforced Advanced Ceramic Composites, in: Annual Bookof ASTM Standards, ASTM, Conshohocken, PA, 1998, p. 581. [13] R.J. Price, J. Nucl. Mater. 33 (1969) 17. [14] R.J. Price, G.R. Hopkins, J. Nucl. Mater. 108&109 (1982) 732. [15] M.C. Osborne, J.C. Hay, L.L. Snead, D. Steiner, J. Am. Ceram. Soc. 82 (1999) 2490. [16] J.H.W. Simmons, Radiation Damage in Graphite, International Series of Monographs in Nuclear Energy, vol. 102, 1965, Pergamon. T. Nozawa et al. / Journal of Nuclear Materials 307–311 (2002) 1173–1177 1177
