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Journal Articles

Structure of nano-size oxides in ODS steels and its stability under electron irradiation

Oka, Keiichiro*; Onuki, Somei*; Yamashita, Shinichiro; Akasaka, Naoaki; Otsuka, Satoshi; Tanigawa, Hiroyasu

Materials Transactions, 48(10), p.2563 - 2566, 2007/10

 Times Cited Count:29 Percentile:78.61(Materials Science, Multidisciplinary)

For understanding the microstructural details of nano-size oxide particles, three types of ODS ferritic and austenitic steels were examined by high voltage electron microscopy, EDS and AP-FIM. The oxide included Y, Ti and O and showed a shell-like structure with different composition. The shell-like structure depends on crystal structure of the matrix during fabrication process. To evaluate the irradiation stability of the oxide particles, the electron irradiation was carried out to 47 dpa in the temperature range between room temperature and 923 K. During the irradiation, the oxide particles did not show obvious change in size. The irradiation behavior is discussed comparing with the results recently reported.

Journal Articles

Effects of microstructural evolution on charpy impact properties of modified ferritic/martensitic steel after neutron irradiation

Yano, Yasuhide; Oka, Keiichiro*; Akasaka, Naoaki; Yoshitake, Tsunemitsu; Abe, Yasuhiro; Onuki, Somei

Journal of Nuclear Science and Technology, 43(6), p.648 - 654, 2006/06

 Times Cited Count:4 Percentile:31.05(Nuclear Science & Technology)

The embrittlement behavior of the modified ferritic/martensitic 11Cr-0.5Mo-2W, V, Nb steel (PNC-FMS) after neutron irradiation in JOYO was investigated by Charpy impact tests and TEM and SEM observations. The impact properties of the specimens after irradiation to 4.4 dpa at 773 K were similar to the as-received PNC-FMS. The ductile-brittle transition temperature (DBTT) remarkably decreased due to irradiation to 2.8 dpa at 923 K. The precipitates formed in the martensitic lath were still stable under neutron irradiation at 773 K, however they were unstable under irradiation at 923 K. The martensitic lath structure was also stable at the former irradiation temperature, but it was significantly changed at the latter. The decrease in the upper shelf energy after irradiation was related to the precipitate distribution. The changes of DBTT due to irradiation were attributed to decreased the dislocation recovery and to increased broadening of the martensitic lath.

Journal Articles

Mechanical properties of small size specimens of F82H steel

Wakai, Eiichi; Otsuka, Hideo*; Matsukawa, Shingo; Furuya, Kazuyuki*; Tanigawa, Hiroyasu; Oka, Keiichiro*; Onuki, Somei*; Yamamoto, Toshio*; Takada, Fumiki; Jitsukawa, Shiro

Fusion Engineering and Design, 81(8-14), p.1077 - 1084, 2006/02

 Times Cited Count:11 Percentile:60.68(Nuclear Science & Technology)

no abstracts in English

Journal Articles

Radiation hardening and -embrittlement due to He production in F82H steel irradiated at 250 $$^{circ}$$C in JMTR

Wakai, Eiichi; Jitsukawa, Shiro; Tomita, Hideki*; Furuya, Kazuyuki; Sato, Michitaka*; Oka, Keiichiro*; Tanaka, Teruyuki*; Takada, Fumiki; Yamamoto, Toshio*; Kato, Yoshiaki; et al.

Journal of Nuclear Materials, 343(1-3), p.285 - 296, 2005/08

 Times Cited Count:48 Percentile:94.02(Materials Science, Multidisciplinary)

The dependence of helium production on radiation-hardening and -embrittlement has been examined in a reduced-activation martensitic F82H steel doped with $$^{10}$$B, $$^{11}$$B and $$^{10}$$B+$$^{11}$$B irradiated at 250$$^{circ}$$C to 2.2 dpa. The total amounts of doping boron were about 60 massppm. The range of He concentration produced in the specimens was from about 5 to about 300 appm. Tensile and fracture toughness tests were performed after neutron irradiation. 50 MeV-He$$^{2+}$$ irradiation was also performed to implant about 85 appm He atoms at 120$$^{circ}$$C by AVF cyclotron to 0.03 dpa, and small punch testing was performed to obtain DBTT. Radiation-hardening of the neutron-irradiated specimens increased slightly with increasing He production. The 100 MPam$$^{1/2}$$ DBTT for the F82H+$$^{11}$$B, F82H+$$^{10}$$B+$$^{11}$$B, and F82H+$$^{10}$$B were 40, 110, and 155$$^{circ}$$C, respectively. The shifts of DBTT due to He production were evaluated as about 70$$^{circ}$$C by 150 appmHe and 115$$^{circ}$$C by 300 appmHe. The DBTT shift in the small punch testing was evaluated as 50$$^{circ}$$C.

Journal Articles

Extra radiation hardening and microstructural evolution in F82H by high-dose dual ion irradiation

Ando, Masami; Wakai, Eiichi; Sawai, Tomotsugu; Matsukawa, Shingo; Naito, Akira*; Jitsukawa, Shiro; Oka, Keiichiro*; Tanaka, Teruyuki*; Onuki, Somei*

JAERI-Review 2004-025, TIARA Annual Report 2003, p.159 - 161, 2004/11

The objectives of this study are to evaluate radiation hardening on ion-irradiated F82H up to 100 dpa and to examine the extra component of radiation hardening due to implanted helium atoms (up to $$sim$$3000 appmHe) in F82H under ratio of 0, 10, 100 appmHe/dpa.The ion-beam irradiation experiment was carried out at the TIARA facility of JAERI. Specimens were irradiated at 633 K by 10.5 MeV Fe ions with/without 1.05 MeV He ions. Micro-indentation tests were performed at loads to penetrate about 0.40 mm in the irradiated specimens using an UMIS-2000. The results are summarized as follows:1) As a result of the single irradiated F82H, the micro-hardness tended to increase about 30 dpa. 2) The extra radiation hardening was obviously caused by co-implanted helium atoms more than 1000 appm in F82H irradiated at 633 K. 3) In the dual-beam (100 appmHe/dpa) irradiated microstructure, nano-voids and fine defects were observed. It is suggested that the formation of nano-voids causes the extra radiation hardening by helium co-implantation.

Journal Articles

Synergistic effect of displacement damage and helium atoms on radiation hardening of F82H at TIARA facility

Ando, Masami; Wakai, Eiichi; Sawai, Tomotsugu; Tanigawa, Hiroyasu; Furuya, Kazuyuki; Jitsukawa, Shiro; Takeuchi, Hiroshi; Oka, Keiichiro*; Onuki, Somei*; Koyama, Akira*

Journal of Nuclear Materials, 329-333(2), p.1137 - 1141, 2004/08

 Times Cited Count:48 Percentile:93.59(Materials Science, Multidisciplinary)

One of the most crucial issues on R&D of reduced activation ferritic/martensitic steels is the effect of helium on the degradation of fracture toughness. The synergistic effects of displacement damage and helium on F82H steel can be partially simulated by martensitic steels doped with $$^{10}$$B or $$^{58}$$Ni in a mixed spectrum fission reactor. However, the control of helium production rate is difficult and the chemical effects of B or Ni doping on mechanical property are not small. Therefore, multi-ion irradiation method is the most convenient and accurate method to simulate various irradiation conditions. Moreover, the effects of helium on irradiation hardening behavior can be examined by combining ion-irradiation with ultra micro-indentation technique. The purpose of this study is to examine the extra component of radiation hardening due to implanted helium in F82H. The extra component of irradiation hardening due to helium was hardly detected in the dual-beam irradiation. Therefore, the effect on irradiation hardening below 630K of helium ($$<$$500 appm) was very small.

Journal Articles

Swelling behavior of F82H steel irradiated by triple/dual ion beams

Wakai, Eiichi; Kikuchi, Kenji; Yamamoto, Shunya; Aruga, Takeo; Ando, Masami; Tanigawa, Hiroyasu; Taguchi, Tomitsugu; Sawai, Tomotsugu; Oka, Keiichiro*; Onuki, Somei*

Journal of Nuclear Materials, 318, p.267 - 273, 2003/05

 Times Cited Count:69 Percentile:96.84(Materials Science, Multidisciplinary)

no abstracts in English

Oral presentation

Behavior of iron in the Yamato Basin and the Japan Basin, Japan Sea

Takata, Hyoe*; Kuma, Kenshi*; Isoda, Yutaka*; Nishioka, Jun*; Otosaka, Shigeyoshi; Chikira, Mitsuru*; Takagi, Shogo*; Kamei, Yoshihiko*; Sakaoka, Keiichiro*

no journal, , 

The authors discussed on the difference of behavior of iron between two basins (the Yamato Basin and Japan Basin) in the Japan Sea by measurements of iron (dissolved and labile dissolved phases) and nutrients in seawater. Concentration of labile dissolved iron in the surface water was about 1.0 nM and did not show difference between the basins. On the other hand, concentration of labile dissolved iron in the Japan Basin increased to 4.5 nM at 1-2 km depth and decreased to 4 nM in the bottom layer. In the Yamato Basin, concentration of labile dissolved iron in deep water increased uniformly and was about 6 nM at the bottom layer. The difference in distribution of iron in seawater indicates that the transport processes of biogenic elements in the deep layers are different between the basins of the Japan Sea.

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