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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:13 Percentile:67.89(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

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:9.11(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

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:16 Percentile:74.49(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:11 Percentile:62.02(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:15 Percentile:72.26(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:33 Percentile:90.19(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

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.

Oral presentation

Rupture properties of plain-woven Tyranno-SA3 CVI SiC/SiC composites

Ozawa, Kazumi; Nozawa, Takashi; Toyoshima, Kazuoki*; Tanigawa, Hiroyasu; Hinoki, Tatsuya*

no journal, , 

no abstracts in English

Oral presentation

Swelling of SiC and its helium effects for expected operating conditions based on some blanket designs using SiC materials

Ozawa, Kazumi; Nozawa, Takashi; Uto, Hiroyasu; Someya, Yoji; Tanigawa, Hiroyasu; Tobita, Kenji

no journal, , 

A silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composite is a promising candidate material for the advanced fusion DEMO blanket. Two options are considered for the use of the composites in the DEMO design: materials functionally used such as a flow channel insert in Pb-Li liquid cooling system, and ones used as a part of structural components. This paper primarily aims (1) to show examples of Japanese blanket concepts, such as SlimCS and VECTOR, which SiC materials are considered to be used, comparing with other US or EU designs, and (2) to summarize/organize the neutron/ion irradiated swelling data currently obtained for the target temperature ranges of mainly $$sim$$700$$^{circ}$$C for functional use and $$sim$$1000$$^{circ}$$C for structural, with a strong emphasis on the effects of helium on swelling of SiC.

Oral presentation

Features of failure behavior of fusion-grade SiC/SiC composites and fundamental concept toward materials codes and standards development

Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu

no journal, , 

It is being proven that fusion-grade SiC/SiC composites are featured in quasi-ductility with progressive fiber pullouts in fracture, strength anisotropy owing to variety of fabric architecture, notch insensitivity about damage tolerance, edge effect on strength and so on by failure evaluation of this class of composites. From these aspects, a unique materials standards and codes should probably be necessary for composites themselves since they are quite different from ductile metals and brittle ceramics. In this paper, a fundamental concept toward materials codes and standards development specific to the fusion-grade SiC/SiC composites and future actions will be discussed based on the recent achievements.

Oral presentation

Changes of microstructure and mechanical properties of Hi-Nicalon Type-S SiC composites irradiated to 100 dpa

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 ~1.0$$times$$10$$^{26}$$ n/m$$^{2}$$ (E $$>$$ 0.1 MeV, equivalent to ~100 dpa) at nominal irradiation temperatures of 300, 500, and 800$$^{circ}$$C. Results of post irradiation experiments including 1/4-four-point flexural tests, SEM, and TEM observation were reported.

Oral presentation

Applicability study of Friction-Stir Process on Cu and its irradiation resistivity

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

no journal, , 

Friction-Stir Process were applied to OFCCu in order to evaluate the applicability of the process to mechanically strengthening pure-Cu and possible structural improvement on CuCrZr alloy. In this study, the tool rotational speed was varied from 50 to 500 rpm in order to clarify the effect of rotational speed on the process. The result showed the achievement of very fine grain structure at the rotational speed of 100 and 200 rpm and also the hardness increase to about 1.5 time higher within the stir-zone than that of the base metal at the most. However, the result also revealed that the rapid decrease of the hardness toward a depth direction and relatively shallow stir-zone depth compared to a length of the pin. This can be explained as post-annealing effect due to a good thermal conductivity of a pure-Cu. To avoid the effect, we are considering to introduce compulsory cooling system during the process, which application is more important to a CuCrZr alloy because more rapid cooling and lower thermal diffusion to base metal are required.

Oral presentation

Damage monitoring of silicon carbide matrix composites by digital image correlation

Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu

no journal, , 

A SiC/SiC composite is a promising candidate material for various engineering applications. For the practical design of composite components, the detailed failure mechanism need to be clarified since composites exhibit unique quasi-ductility in fracture. Focusing on the surface flaw issue, identifying notch sensitivity is essential to judge damage tolerance of composite materials. To date, it is convinced that composites with moderate fiber/matrix interface are generally notch insensitive. However, recent work by the authors claimed indicative notch sensitivity of advanced SiC/SiC composites by the off-axial tensile loading case. This study aims to identify the detailed damage accumulation behavior of this class of composites to fully understand their notch sensitivity. For that purpose, the digital image correlation (DIC) technique, which becomes a potential powerful tool to understand the detailed failure mechanism of composites, is specifically adopted to get a local strain distribution profile near the notch tip.

Oral presentation

Rupture properties of advanced SiC/SiC composites and development of strain measurement for evaluating creep properties

Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu

no journal, , 

no abstracts in English

Oral presentation

Modification of vacuum plasma sprayed tungsten coating by friction stir processing

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

no journal, , 

no abstracts in English

39 (Records 1-20 displayed on this page)