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Kim, B. K.*; Tan, L.*; Sakasegawa, Hideo; Parish, C. M.*; Zhong, W.*; Tanigawa, Hiroyasu*; Kato, Yutai*
Journal of Nuclear Materials, 545, p.152634_1 - 152634_12, 2021/03
Times Cited Count：1 Percentile：16.35(Materials Science, Multidisciplinary)Hirose, Takanori; Nozawa, Takashi; Stoller, R. E.*; Hamaguchi, Dai; Sakasegawa, Hideo; Tanigawa, Hisashi; Tanigawa, Hiroyasu; Enoeda, Mikio; Kato, Yutai*; Snead, L. L.*
Fusion Engineering and Design, 89(7-8), p.1595 - 1599, 2014/10
Times Cited Count：47 Percentile：96.65(Nuclear Science & Technology)The material properties, focusing on the properties used for design analysis were re-assessed and newly investigated for various heats including F82H-IEA. Moreover, irradiation effects on those properties were studied in this work. As for thermal properties, thermal conductivity that has significant impacts on the thermo-hydraulic properties of the blanket was investigated on several heats of F82H including F82H-IEA. According to the measurements, the thermal conductivity falls in the range 28.3
1.1 W/m/K at 293 K. Although this is comparable with that of the other ferritic/martensitic steels, it is 20% lower than the published value for F82H-IEA. The re-assessment on the published value revealed that the thermal diffusivity was over-estimated. As for irradiation effects on the physical properties, electric resistivity was measured after irradiation up to 6 dpa at 573 K and 673 K. The reduction of resistivity in F82H and its welds were 3% and 6%, respectively.
Takizawa, Kentaro*; Kakehashi, Kazuyuki*; Fukuda, Toshiaki*; Kida, Toru*; Sawa, Kazuhiro; Sumita, Junya; Kato, Yutai*; Snead, L. L.*
Ceramic Materials for Energy Applications; Ceramic Engineering and Science Proceedings, Vol.32, No.9, p.13 - 19, 2011/11
Fine-grained isotropic graphite shows high strength making it a promising material for the graphite component of High Temperature Gas-cooled Reactor (HTGR) and Very High Temperature Reactor (VHTR). Service life of the graphite component is determined primarily by the residual strength after neutron irradiation in the reactor core. It is expected that development of a new nuclear grade graphite possessing higher strength will contribute toward added design margins and an extension of the service life of components, which likely improve the reactor economy very significantly. Tokai Carbon Co. LTD. has started the development of nuclear grade graphite for the graphite component of VHTR. G347S and G458S grades are fine-grained isotropic graphites having high tensile strength greater than 30 MPa. It is planned to carry out the neutron irradiation tests using High Flux Isotope Reactor at Oak Ridge National Laboratory up to the neutron fluence of 30 dpa and the irradiation temperatures of 300-900
C. The dimensional changes, elastic modulus, coefficient of thermal expansion, etc., will be studied. It is also planned to evaluate the non-irradiated mechanical/thermal properties and the irradiation effects in collaboration with Japan Atomic Energy Agency. This paper introduces our technical R&D plan for G347S and G458S. The initial results of the properties and the irradiation test plan are also shown.
Hirose, Takanori; Okubo, Nariaki; Tanigawa, Hiroyasu; Kato, Yutai*; Clark, A. M.*; McDuffee, J. L.*; Heatherly, D. W.*; Stoller, R. E.*
DOE/ER-0313/49, p.94 - 99, 2010/12
Nozawa, Takashi; Hinoki, Tatsuya*; Hasegawa, Akira*; Koyama, Akira*; Kato, Yutai*; Snead, L. L.*; Henager, C. H. Jr.*; Hegeman, J. B. J.*
Journal of Nuclear Materials, 386-388, p.622 - 627, 2009/04
Times Cited Count：115 Percentile：99.19(Materials Science, Multidisciplinary)A new class SiC/SiC composite have been developed for fusion. While the development efforts has resulted in a radiation-resistant SiC/SiC, development continues to improve on engineering properties of this composite. With the completion of the "proof-of-principal" phase, the R&D on SiC/SiC is now shifting to the more pragmatic phase of material data-basing. Critical application issues still remain, including (1) heavy irradiation effect with considerations of He/H synergistic effects and irradiation creep, (2) erosion-corrosion behavior, (3) nuclear transmutation other than He/H, and (4) joining. Understanding the irradiation effect on electrical conductivity is another important issue for the FCI application. Along with the review in material development, characterization, and irradiation effect studies, this paper provides an introductive work toward standardization of the test methodology.
Igawa, Naoki; Taguchi, Tomitsugu; Nozawa, Takashi*; Snead, L. L.*; Hinoki, Tatsuya*; McLaughlin, J. C.*; Kato, Yutai*; Jitsukawa, Shiro; Koyama, Akira*
Journal of Physics and Chemistry of Solids, 66(2-4), p.551 - 554, 2005/02
Times Cited Count：47 Percentile：82.48(Chemistry, Multidisciplinary)Silicon carbide is an important engineering ceramic because of its high strength and stability at high temperature and low induced radioactivity after neutron irradiation. Though monolithic SiC is brittle and low toughness, SiC fiber reinforced SiC matrix composites significantly improve these properties and therefore are attractive candidate materials for fusion reactor structural applications. Recently, stoichiometric SiC fibers with superior mechanical properties have been produced. We carried out the optimization of interface and composite fabrication using the chemical vapor infiltration, which is the one of the best techniques to fabricate the SiC composite. The composite with higher density and homogeneous matrix was obtained by the optimization of materials and carrier gas flow rate. The porosity was decreased with increasing the fiber volume fraction. We adopted the carbon or carbon/SiC interface between fiber and matrix and we found that the dependence of interface thickness on the tensile properties was small in the interface thickness from 50 to 300 nm.
Taguchi, Tomitsugu; Nozawa, Takashi*; Igawa, Naoki; Kato, Yutai*; Jitsukawa, Shiro; Koyama, Akira*; Hinoki, Tatsuya*; Snead, L. L.*
Journal of Nuclear Materials, 329-333(Part1), p.572 - 576, 2004/08
Times Cited Count：46 Percentile：92.89(Materials Science, Multidisciplinary)The SiC/SiC composite with SiC/C multi-layer interphase coated on advanced SiC fibers was fabricated by the forced thermal-gradient chemical vapor infiltration (F-CVI) process for improvement in mechanical properties. The SEM and TEM observation verified that SiC/C multi-layer interphase was formed on SiC fibers. The both flexural and tensile strengths of SiC/SiC composite with SiC/C multi-layer interphase were approximately 10 % higher than that with single carbon interphase. The SEM observation on the fracture surface of the composite with SiC/C multi-layer reveals that cylindrical steps around the fiber were formed. The several crack deflections occurred within SiC/C multi-layer interphase. The SiC/C multi-layer applied in this study operated efficiently to improve the mechanical properties.
Koyama, Akira*; Donomae, Takako; Kato, Yutai
JNC TY9400 2000-017, 65 Pages, 2000/03
JNC-TY9400-2000-017.pdf:9.69MB
no abstracts in English
Nozawa, Takashi; Kato, Yutai*; Snead, L. L.*
no journal, ,
This study aims to identify the effect of neutron irradiation on the fiber/matrix interface of advanced SiC/SiC composites. A single fiber push-out test was applied to evaluate the shear properties at the interface. The results indicate that the interfacial shear strength depends significantly on the irradiation temperature and neutron dose up to 7.7 dpa at 
1080C. It is worth noting that no major deterioration of the bulk strength of the composites is expected by the slight decrease of interfacial shear properties. This paper will report the general guideline to design irradiation resistant fiber/matrix interface and critical issues for further development will be discussed.
Nozawa, Takashi; Kato, Yutai*; Kishimoto, Hirotatsu*; Koyama, Akira*
no journal, ,
One of the advantages for highly-crystalline and stoichiometric silicon carbide (SiC) composites (advanced SiC/SiC) is improved stability of chemical, physical and mechanical properties at high-temperatures. Besides, it has been revealed that significant contribution from the optimized fiber/matrix (F/M) interface enables to give good quasi-ductility beyond matrix cracking. Though the importance of the F/M interfacial role is recognized, understanding the mechanism of crack propagation is insufficient. Meanwhile, the existing test methods to determine fracture resistance of composites, i.e., a critical energy required to propagate a crack, are not fully established because of very limited considerations on the influence of irreversible energies emerged by interaction at the F/M interface and microcrack forming. This study aims to develop a fracture resistance test methodology and to quantify the crack resistance of advanced SiC/SiC composites.
Nozawa, Takashi; Kato, Yutai*; Kishimoto, Hirotatsu*
no journal, ,
One of the perceived advantages for highly-crystalline and stoichiometric SiC and SiC/SiC composites is the retention of fast fracture properties after neutron irradiation. Specifically, it has been clarified that the maximum allowable stress (or strain) limit seems unaffected in certain irradiation conditions. Meanwhile, understanding the mechanism of crack propagation from flaws is somehow lacking. This study aims to evaluate crack propagation behaviors of advanced SiC/SiC and to provide fundamentals on fracture resistance of the composites to define the strength limit for the practical component design. For those purposes, the effects of irreversible energies related to interfacial debonding, fiber bridging, and microcrack forming on the fracture resistance were evaluated.
Kunimoto, Eiji; Konishi, Takashi; Eto, Motokuni*; Fujita, Ichiro; Shibata, Taiju; Sawa, Kazuhiro; Kato, Yutai*
no journal, ,
no abstracts in English
Kunimoto, Eiji; Konishi, Takashi; Eto, Motokuni*; Sumita, Junya; Shibata, Taiju; Sawa, Kazuhiro; Kuroda, Masatoshi*; Kato, Yutai*
no journal, ,
no abstracts in English
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu; Kato, Yutai*; Snead, L. L.*
no journal, ,
An advanced SiC/SiC composite is a candidate material for fusion DEMO reactor. Four types of model unidirectional SiC/SiC composites (minicomposites) with variations in fiber (Hi-Nicalon Type-S (HNLS), Tyranno-SA3, Sylramic and Sylramic-iBN) by chemical vapor infiltration method were evaluated for tensile and fiber/matrix interfacial properties. The ultimate tensile strength (UTS) increased with the interfacial sliding stress (
) obtained by the hysteresis loop analysis for Tyranno-SA3, Sylramic and Sylramic-iBN. However, this was not the case for the HNLS composite. The composite achieved high UTS due to very low , arising from the larger residual radial tensile stress and smooth fiber surface. In contrast, the fracture behavior of the other composites may have been strongly affected by the clamping stress produced by the relatively rough fiber surfaces.
Ozawa, Kazumi; Kato, Yutai*; Nozawa, Takashi; Snead, L. L.*
no journal, ,
Advanced SiC/SiC composites are candidates for the advanced blanket material for fusion DEMO reactor. In order to investigate the effects of neutron irradiation on fracture resistance, the composites after neutron irradiation to 
5.9 
10
n/m
(
0.1 MeV) at 800 and 1300C were evaluated by three-point single edge notched bend miniature test. Taking all results into consideration for the global energy balance analysis based on the non-linear fracture mechanics, the previous tensile tests, and the hysteresis loop analysis for interfacial property evaluation, it was concluded that the effects of neutron irradiation in conditions studied on fracture resistance of the composites appeared insignificant.
Ozawa, Kazumi; Kato, Yutai*; Nozawa, Takashi; Tanigawa, Hiroyasu; Snead, L. L.*
no journal, ,
An advanced SiC/SiC composite is very attractive as an advanced blanket material for fusion DEMO reactor. In this study, tensile and fiber/matrix interfacial properties of unirradiated SiC/SiC minicomposites were evaluated in order to examine the effects of difference of fiber and interphase thickness. The experiments revealed that fiber surface roughness directly correlates with interfacial sliding stress and that the relationship can affects ultimate tensile stress. Additionally the dependence of interphase thickness on tensile and interfacial strength was also confirmed.
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu; Kato, Yutai*; Snead, L. L.*
no journal, ,
A silicon carbide (SiC) matrix composite is a promising candidate for nuclear fusion energy applications. Unloading-reloading cyclic tensile tests were conducted to estimate interfacial properties for unidirectional SiC/SiC minicomposites reinforced by Hi-Nicalon Type-S (HNLS) or Tyranno-SA3 SiC fibers via CVI process were conducted. The interfacial properties were also evaluated by fiber push-out test. According to these results, it is implied that both fiber surface roughness and interfacial layter thickness can impact the tensile and interfacial properties.
Ozawa, Kazumi; Koyanagi, Takaaki*; Nozawa, Takashi; Kato, Yutai*; Kondo, Sosuke*; Tanigawa, Hiroyasu; Snead, L. L.*
no journal, ,
A silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite is a promising candidate material for an advanced fusion DEMO blanket. High-dose irradiation experiments were performed with our special focuses on understanding; (1) integrity of the Hi-Nicalon Type-S (HNLS) composites, (2) functionality of thin pyrocarbon (PyC) /SiC multilayer, and (3) clarifying the mechanism underlying degradation, as feedback to R&D on SiC/SiC composites. The materials used in this study were plain-weave HNLS composites produced via the chemical vapor infiltration process. Neutron irradiation was conducted in the HFIR at ORNL. The peak neutron fluence was ~1.010
n/m (E 0.1 MeV, equivalent to ~100 dpa) at nominal irradiation temperatures of 300, 500, and 800C. Results of post irradiation experiments including 1/4-four-point flexural tests, SEM, and TEM observation were reported.
Ozawa, Kazumi; Koyanagi, Takaaki*; Nozawa, Takashi; Kato, Yutai*; Kondo, Sosuke*; Tanigawa, Hiroyasu; Snead, L. L.*
no journal, ,
A silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite is a promising candidate material for an advanced fusion DEMO blanket because of the excellent thermo-mechanical / -chemical properties and irradiation tolerance of SiC itself. The irradiation response of highly-crystalline and near-stoichiometric SiC fiber has been assumed to be the same as that of high purity monolithic 
-SiC. Unfortunately, based on recent data this assumption appears not to be correct. This study mainly aims to investigate mechanical and microstructural changes of the SiC/SiC composite after neutron irradiation to higher dose. In the post neutron irradiation experiments to 100 dpa, ~50% degradation of proportional limit stress and ultimate flexural strength was observed for the composite irradiated at 629C, while the one irradiated at 319C exhibited brittle behavior. In the ion-experiment results, shrinkage of the HNLS fiber was observed for specimens irradiated at 300 and 600C to 100 dpa. The FE-TEM results, EELS analysis and previous our works suggest that the shrinkage would be responsible for the transport of excess carbon atoms from intergranular phase into SiC grains.
Tanigawa, Hiroyasu; Sakasegawa, Hideo; Hirose, Takanori; Kato, Yutai*
no journal, ,
Reduced activation ferritic/martensitic steel, F82H, is the first candidate DEMO blanket structural material, and the preparation of high dose irradiation database is underway. 87 dpa irradiation was completed and post irradiation tensile tests were conducted at the irradiation temperature. The results of the tensile test and fractography on 300C irradiated specimens will be reported.
