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Journal Articles

Impacts of friction stir processing on irradiation effects in vacuum-plasma-spray coated tungsten

Ozawa, Kazumi; Tanigawa, Hiroyasu; Morisada, Yoshiaki*; Fujii, Hidetoshi*

Fusion Engineering and Design, 98-99, p.2054 - 2057, 2015/10

 Times Cited Count:1 Percentile:83.34(Nuclear Science & Technology)

Reduced activation ferritic/martensitic steel, as typified by F82H, is a promising candidate for structural material of DEMO fusion reactors. To prevent plasma sputtering, tungsten (W) coating was essentially required. This study aims to examine the irradiation effects on hardness and microstructure of vacuum-plasma-spray coated W-F82H steel, with a special emphasis on the impacts of grain-refining induced by frictional stir processing (FSP). It was revealed that the hardness of the VPS-FSP W after ion-irradiation to 5.4 dpa at 800$$^{circ}$$C were not remarkably changed, where bulk W usually exhibited significant irradiation hardening.

Journal Articles

Modification of vacuum plasma sprayed tungsten coating on reduced activation ferritic/martensitic steels by friction stir processing

Tanigawa, Hiroyasu; Ozawa, Kazumi; Morisada, Yoshiaki*; Noh, S.*; Fujii, Hidetoshi*

Fusion Engineering and Design, 98-99, p.2080 - 2084, 2015/10

 Times Cited Count:6 Percentile:31.94(Nuclear Science & Technology)

The vacuum plasma spray (VPS) technique has been investigated as the most practical method to form Tungsten (W) layer as a plasma facing material in fusion devices. The issues are the thermal conductivity and the strength of VPS-W, i.e., the thermal conductivity of VPS-W were significantly lower than that of the bulk W, and the hardness of VPS-W is much less than that of the bulk W. These are mainly caused by the porous structure of VPS-W. In order to solve these issues, friction stir processing (FPS) was applied on VPS-W in this study. It was suggested that FSP can contribute to significant improvement both in mechanical and thermal properties of VPS-W coating.

Journal Articles

Evaluation of damage accumulation behavior and strength anisotropy of NITE SiC/SiC composites by acoustic emission, digital image correlation and electrical resistivity monitoring

Nozawa, Takashi; Ozawa, Kazumi; Asakura, Yuki*; Koyama, Akira*; Tanigawa, Hiroyasu

Journal of Nuclear Materials, 455(1-3), p.549 - 553, 2014/12

 Times Cited Count:9 Percentile:24.83(Materials Science, Multidisciplinary)

SiC/SiC composite is a promising candidate material of fusion DEMO reactor. This paper aims to identify its damage tolerance and strength anisotropy by various characterization techniques such as acoustic emission (AE) monitoring, electrical resistivity (ER) measurement, and digital image correlation (DIC). The AE results identified that damage accumulation initiated prior to the proportional limit stress (PLS) by both tensile and compressive loadings for 2D composites. The preliminary AE waveform analysis implied that this AE detect strength corresponds to initiation of micro-cracking but the stress-strain curve shows further linearity due to the strong interfacial friction. Then fiber sliding occurred near the PLS, followed by the non-linearlity of the curve. The preliminary tensile test results using a notched specimen also suggest notch insensitivity of the composites in any loading directions. The detailed failure mechanism will eventually be discussed with ER and DIC results.

Journal Articles

Stress envelope of silicon carbide composites at elevated temperatures

Nozawa, Takashi; Kim, S.*; Ozawa, Kazumi; Tanigawa, Hiroyasu

Fusion Engineering and Design, 89(7-8), p.1723 - 1727, 2014/10

 Times Cited Count:5 Percentile:46.19(Nuclear Science & Technology)

A SiC/SiC composite is a promising candidate material for the advanced fusion DEMO blanket. For the design of the DEMO, the stability of high-temperature strength of SiC/SiC composites needs to be identified. Additionally, strength anisotropy needs to be clarified because of its unique fabric architecture. This study therefore aims to evaluate mechanical properties by various modes at elevated temperatures, eventually providing a stress envelope for the design. A P/W Tyranno-SA3 fiber reinforced CVI SiC matrix composite with multilayered SiC/PyC interface was evaluated in this study. Tensile and compressive tests were conducted by the SSTT specifically arranged for the high-temperature use. In-plane shear properties were contrarily estimated by the off-axial tensile method assuming that the mixed mode failure criterion is valid for composites. All tests were performed in vacuum. The preliminary test results indicate no degradation of both proportional limit stress (PLS) and the ultimate tensile strength at temperatures below 1000$$^{circ}$$C. Similarly, no significant degradation of high-temperature compressive and in-plane shear properties were identified, finally providing the stress envelope at elevated temperatures for the design.

Journal Articles

Re-defining failure envelopes for silicon carbide composites based on damage process analysis by acoustic emission

Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu

Fusion Engineering and Design, 88(9-10), p.2543 - 2546, 2013/10

 Times Cited Count:11 Percentile:22.08(Nuclear Science & Technology)

A SiC/SiC composite is a promising candidate for a fusion DEMO blanket. Due to the inherent quasi-ductile failure of composites, determining failure scenario for this class of composites is undoubtedly important to develop design codes in practical use of them. This study aims to evaluate the failure behavior of the quasi-ductile SiC/SiC composites to provide a strength map. For this purpose, detailed tensile, compressive and in-plane shear failure behaviors were evaluated by the acoustic emission (AE) technique. The AE results distinguished damage accumulation processes by wavelet analysis. Of particular emphasis is that matrix cracking occurred prior to the PLS by both tensile and compressive loadings because the rough-surface of SiC fibers resulted in the strong frictional stress at the fiber/matrix (F/M) interface. In this paper, an updated failure envelope will be provided by referring the actual matrix cracking stresses as more realistic and reasonable failure criteria.

Journal Articles

Characterization of failure behavior of silicon carbide composites by acoustic emission

Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu

Ceramic Materials for Energy Applications II, p.95 - 110, 2012/11

This study aims to identify failure behavior of SiC/SiC composites by varied test modes. For this purpose, acoustic emission (AE) was applied to detect composites' failure. Tensile and compressive tests were conducted for a plain-weave (P/W) chemical vapor infiltration (CVI) composite. Various loading angles were applied to discuss an anisotropic issue. AE results distinguished damage accumulation processes in axial and off-axial loading cases. Specifically, test results indicated a clear difference of damage density between tensile and compressive tests. This study also classified the characteristic failure modes by separately discussing localized variations of power within a time series by wavelet analysis.

Journal Articles

Determination and prediction of axial/off-axial mechanical properties of SiC/SiC composites

Nozawa, Takashi; Ozawa, Kazumi; Choi, Y.-B.*; Koyama, Akira*; Tanigawa, Hiroyasu

Fusion Engineering and Design, 87(5-6), p.803 - 807, 2012/08

 Times Cited Count:20 Percentile:10.19(Nuclear Science & Technology)

A SiC/SiC composite is a candidate material for a demonstration fusion power reactor. Considering the inherent anisotropy of composites with variety of fabric architecture is required to precisely predict axial and off-axial mechanical properties by various failure modes. This study evaluated crack propagation behavior by the various modes to provide a strength anisotropy map and we discussed a methodology to analytically predict this trend. The strength anisotropy maps identified for various fabric orientations clearly indicate that the composites failed by the mixed modes. Specifically, due to the axial anisotropy, five individual modes such as tensile/compressive strengths in the axial/transverse directions, respectively, as well as the in-plane shear strength, are identified to be essential. In this study, with the analytical criterion based on the Tsai-Wu model, the strength anisotropy could satisfactorily be described.

JAEA Reports

Plan and reports of coupled irradiation (JRR-3 and JOYO of research reactors) and hot facilities work (WASTEF, JMTR-HL, MMF and FMF); R&D project on irradiation damage management technology for structural materials of long-life nuclear plant

Matsui, Yoshinori; Takahashi, Hiroyuki; Yamamoto, Masaya; Nakata, Masahito; Yoshitake, Tsunemitsu; Abe, Kazuyuki; Yoshikawa, Katsunori; Iwamatsu, Shigemi; Ishikawa, Kazuyoshi; Kikuchi, Taiji; et al.

JAEA-Technology 2009-072, 144 Pages, 2010/03

JAEA-Technology-2009-072.pdf:45.01MB

"R&D Project on Irradiation Damage Management Technology for Structural Materials of Long-life Nuclear Plant" was carried out from FY2006 in a fund of a trust enterprise of the Ministry of Education, Culture, Sports, Science and Technology. The coupled irradiations or single irradiation by JOYO fast reactor and JRR-3 thermal reactor were performed for about two years. The irradiation specimens are very important materials to establish of "Evaluation of Irradiation Damage Indicator" in this research. For the acquisition of the examination specimens irradiated by the JOYO and JRR-3, we summarized about the overall plan, the work process and the results for the study to utilize these reactors and some facilities of hot laboratory (WASTEF, JMTR-HL, MMF and FMF) of the Oarai Research-and-Development Center and the Nuclear Science Research Institute in the Japan Atomic Energy Agency.

Oral presentation

R&D project on irradiation damage management technology for structural materials of long-life nuclear plant, 3; Assembly and disassembly techniques of JRR-3 re-irradiation capsule in WASTEF

Usami, Koji; Ichise, Kenichi; Numata, Masami; Endo, Shinya; Onozawa, Atsushi; Takahashi, Hiroyuki; Kikuchi, Taiji; Ishikawa, Kazuyoshi; Yoshikawa, Katsunori; Nakata, Masahito; et al.

no journal, , 

In the R&D Project on Irradiation Damage Management Technology for Structural Materials of Long-life Nuclear Plant, the specimens to be obtained by coupling irradiation between JOYO and JRR-3 is necessary to establish the evaluation method by using the irradiation damage indicator of them. Therefore, the techniques for assembling of JRR-3 re-irradiation capsule in the Waste Safety Testing Facility (WASTEF) were developed to perform the coupling irradiation. The techniques contributed to the first coupling irradiation in the world.

Oral presentation

Interfacial property evaluation of SiC/SiC model composites

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 ($$tau$$) 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 $$tau$$, 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.

Oral presentation

Evaluation of damage tolerance of neutron-irradiated SiC/SiC composites

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 $$sim$$5.9 $$times$$ 10$$^{25}$$ n/m$$^{2}$$ (${it E}$ $$>$$ 0.1 MeV) at 800 and 1300$$^{circ}$$C 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.

Oral presentation

Strength and interfacial properties of single fiber-tow CVI SiC/SiC minicomposites

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.

Oral presentation

Interfacial property evaluation of SiC/SiC model composites by single fiber push-out test

Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu

no journal, , 

Interfacial properties of unidirectional CVI SiC/SiC minicomposites reinforced with Hi-Nicalon Type-S (HNLS) and Tyranno-SA3 were evaluated. Only HNLS minicomposites with 240- and 1150-nm-thick PyC interphases exhibited a pseudo-ductile behavior. Brittle fracture behavior of other minicomposites was attributed primarily to quite low fiber volume fraction. The HNLS minicomposites with 240-nm-thick exhibited an ultimate tensile strength equivalent to 79-104% of the fiber bundle strength but only 70-85% of the strength of 1150-nm-thick. Based on hysteresis loop analysis, sliding stress estimated for the 240-nm-thick appeared to be about 1.4 times as that for the 1150-nm-thick. This shows that both composites satisfy the GLS condition, but the composite with the thicker interphase could not achieve its fiber bundle strength, probably due to the lower interfacial sliding stress.

Oral presentation

Tensile and interfacial strength evaluation of SiC/SiC model composites

Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu

no journal, , 

Tensile and interfacial properties of unidirectional SiC/SiC model composites reinforced with Hi-Nicalon Type-S fibers with innermost pyrolytic carbon (PyC) layer thickness of $$sim$$240 and $$sim$$1150 nm (TypeS-240 and TypeS-1150, respectively) were evaluated by unloading/reloading cyclic tensile tests and single fiber push-out tests. Effective fiber bundle strength in the TypeS-240 and -1150 composites were 79-104% and 70-85%, compared with the original fiber bundle strength. According to the analytic results using hysteresis loops of tensile curves, interfacial sliding stress of the TypeS-1150 estimated to be about 0.7 times as large as the TypeS-240. This tendency was also confirmed by the single fiber push-out tests. These composites showed quasi-ductility, but it is considered that the composite with the thicker interphase could not achieve its fiber bundle strength, probably due to the lower interfacial sliding stress.

Oral presentation

Evaluation of failure behavior of fusion-grade SiC/SiC composites by acoustic emission

Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu

no journal, , 

One of big advantages to utilize fusion-grade SiC/SiC composites is to obtain quasi-ductility by fiber pullouts at the fiber/matrix (F/M) interface. This study primarily aims to identify the detailed failure process of this class of composites by the acoustic emission technique. Specifically, the first attempt of the wavelet analysis is enable to evaluate the time-dependent behavior of AE response during the failure process. Test results show the crack initiation below the proportional limit stress in the stress vs. strain curve, followed by non-linear behavior by sliding at the proportional limit. The strong interfacial bonding and friction due to the rough fiber surface of the fusion-grade SiC/SiC composites sustain load even after matrix cracking until the load achieved the proportional limit and this is totally different from the behavior of the conventional weak interface composites.

Oral presentation

Tensile and interfacial properties of SiC/SiC minicomposites

Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu

no journal, , 

A silicon carbide (SiC) matrix composite is a promising candidate for nuclear fusion energy applications. In order to design a damage tolerant composite, fiber/matrix interfacial properties with and without irradiation effects should be thoroughly and systematically understood. For this purpose an approach using model composites is considered to be suitable. This study examines the effects of different fibers and interphases on tensile and interfacial properties of non-irradiated SiC/SiC minicomposites which have high crystalline and near stoichiometric SiC fibers. As a result of the tensile unloading-reloading cyclic tests, following analysis of the hysteresis loops, and the single fiber push-out tests, (1) fiber surface roughness can significantly affect interfacial sliding stress and hence each tensile characteristic such as tensile strength/strain and hysteresis loop width, and (2) interphase thickness would also influence the interfacial and tensile properties.

Oral presentation

Microstructure investigation on SiC by nano-infiltration transient eutectic process after triple ion beam bombardment

Ozawa, Kazumi; Koyanagi, Takaaki*; Taguchi, Tomitsugu; Nozawa, Takashi; Tanigawa, Hiroyasu; Kondo, Sosuke*; Hinoki, Tatsuya*

no journal, , 

A SiC/SiC composite is a promising candidate functional/structural material for fusion DEMO reactor. To examine the effects of transmuted H mainly on microstructural cavity formation, the monolithic NITE-SiC with 6wt% Y$$_{2}$$O$$_{3}$$-Al$$_{2}$$O$$_{3}$$ sintering additive system were ion-irradiated to 10 dpa at 1000$$^{circ}$$C nominally with 130 appmHe/dpa, and 40 or 400 appmH/dpa, respectively. In SiC grains, tiny cavities with 2 nm formed densely. However, it is revealed that H could not remarkably impact on cavity formation (size, density) in the condition studied. The influence of cavities formed along SiC-YAG grain boundary (GB) on cavity swelling seems to be also small, possibly attributed to its quite low density, even though the cavity size formed is three to five times larger than the size in CVI-SiC matrix in the same irradiation condition. Additional investigation of the microstructural evolution in YAG grain and SiC-YAG GB is a future plan.

Oral presentation

Effects of transmuted hydrogen on microstructure of SiC by nano-infiltration transient eutectic process after triple ion beam irradiation

Ozawa, Kazumi; Koyanagi, Takaaki*; Taguchi, Tomitsugu; Nozawa, Takashi; Tanigawa, Hiroyasu; Kondo, Sosuke*; Hinoki, Tatsuya*

no journal, , 

no abstracts in English

Oral presentation

Evaluation of inter-laminar shear behavior of fusion-grade SiC/SiC composites by the digital image correlation method

Nozawa, Takashi; Nakata, Toshiya; Ozawa, Kazumi; Tanigawa, Hiroyasu

no journal, , 

no abstracts in English

Oral presentation

Tensile and interfacial properties of unidirectional advanced SiC/SiC minicomposites

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.

37 (Records 1-20 displayed on this page)