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Sato, Yutaka*; Kokawa, Hiroyuki*; Fujii, Hiromichi*; Yano, Yasuhide; Sekio, Yoshihiro
Metallurgical and Materials Transactions A, 46(12), p.5789 - 5800, 2015/12
Times Cited Count：15 Percentile：58.53(Materials Science, Multidisciplinary)Dissimilar friction stir welding (FSW) of an 11% Cr ferritic/martensitic stee (PNC-FMS) to 316-grade austenitic stainless steel was attempted with a view to its potential application to the wrapper tubes of next-generation fast reactors. The mechanical properties and microstructure of the resulting welds were systematically examined, which revealed that FSW produces a defect-free stir zone in which material intermixing is notably absent. That is, both steels are separately distributed along a zigzagging interface in the stir zone when PNC-FMS is placed on the retreating side, with the tool plunging at the butt line. This interface did not act as a fracture site during small-sized tensile testing of the stir zone. Furthermore, the microstructure of the stir zone was refined in both the PNC-FMS and 316 stainless steel sides, resulting in improved mechanical properties over the respective base material regions.
Yano, Yasuhide; Sato, Yutaka*; Sekio, Yoshihiro; Otsuka, Satoshi; Kaito, Takeji; Ogawa, Ryuichiro; Kokawa, Hiroyuki*
Journal of Nuclear Materials, 442(1-3), p.S524 - S528, 2013/09
Times Cited Count：14 Percentile：72.14(Materials Science, Multidisciplinary)Friction stir welding was applied to the wrapper tube materials, 11Cr-ferritic/martensitic steel, intended for fast reactors and defect-free welds were successfully produced. Then, the mechanical and microstructural properties of the friction stir welded steel were investigated. The hardness values of the stir zone were about 550 Hv, and they had hardly any dependence on the rotational speed, although they were much higher than that of the base material. However, tensile strengths and elongations of the stir zones were better at 298 K, compared to those of the base material. These excellent tensile properties were attributable to the fine grain formation during friction stir welding. A part of this study is the result of "Friction stir welding of the wrapper tube materials for Na fast reactors" carried out under the Strategic Promotion Program for Basic Nuclear Research by the Ministry of Education, Culture, Sports, Science and Technology of Japan.
Sato, Yutaka*; Kokawa, Hiroyuki*; Yano, Yasuhide; Sekio, Yoshihiro
Friction Stir Welding and Processing, 7, p.91 - 99, 2013/03
PNC-FMS is a newly developed 11Cr-ferritic/martensitic steel with good swelling resistance, designed for the wrapper tubes of fast reactors. In this study, friction stir welding (FSW) was attempted as a welding process of PNC-FMS because fusion welding of this steel significantly reduced mechanical properties through formation of brittle microstructure. FSW was applied to PNC-FMS at 100 to 300 rpm using Q60 tool, and defect-free welds were obtained. The stir zones had fine microstructure with ferrite and martensite, and the grain size and fraction of martensite increased with rotational speed. Since all welds were overmatched, all transverse tensile specimens were broken at the base material region. The tensile test of the stir zone clarified that the stir zone produced at 100 rpm exhibited higher strengths and elongation than the base material. This study showed that FSW at lower rotational speed produced the stir zone having better mechanical properties in PNC-FMS.
Saito, Shigeru; Kikuchi, Kenji*; Hamaguchi, Dai; Tezuka, Masao*; Miyagi, Masanori*; Kokawa, Hiroyuki*; Watanabe, Seiichi*
Journal of Nuclear Materials, 431(1-3), p.91 - 96, 2012/12
Times Cited Count：16 Percentile：75.52(Materials Science, Multidisciplinary)To evaluate lifetime of structural materials for ADS, corrosion tests in LBE have been done at JAEA. The corrosion test was performed by using JAEA lead-bismuth flowing loop (JLBL-1). Experimental condition was as follows; The temperature of high and low temperature parts of the loop were 450
C and 350C, respectively. Flowing velocity at the test specimens was about 1m/s. Plate type SS316L-BM and SS316L-GBEM were used as a specimens. After the 3,000 hours operation, the test specimens were cut and macroscopic observation was carried out. The result showed that both materials were intensively eroded. Corrosion depth and LBE penetration through grain boundaries of GBEM were smaller than these of 316SS-BM.
Sakuma, Takashi*; Mohapatra, S. R.*; Yokokawa, Jo*; Shimizu, Norifumi*; Isozaki, Nobuhiro*; Uehara, Hiroyuki*; Xianglian*; Basar, K.*; Takahashi, Haruyuki*; Kamishima, Osamu*; et al.
Proceedings of 12th Asian Conference on Solid State Ionics and 15th Chinese Conference on Solid State Ionics, p.439 - 445, 2010/00
Diffuse neutron scattering intensities from ionic crystals, covalent crystals and metal crystals are analyzed by including the correlation effects among thermal displacements of atoms into the function describing background intensity. The obtained values of correlation effects among first nearest neighboring atoms are 0.7 near room temperature. The values of the correlation effects do not depend much on the type of the crystal binding near room temperature. The values of correlation effects decrease rapidly with the increase of inter-atomic distances. The correlation effects also decrease with the decrease of temperature.
Kokawa, Hiroyuki*; Shimada, Masayuki*; Wang, Z.*; Sato, Yutaka*; Sato, Yoshihiro*; Kiuchi, Kiyoshi
JAERI-Tech 2003-014, 22 Pages, 2003/03
JAERI-Tech-2003-014.pdf:1.68MB
no abstracts in English
Tanikawa, Ryusuke*; Sakaguchi, Norihito*; Watanabe, Seiichi*; Kinoshita, Hiroshi*; Kokawa, Hiroyuki*; Kawai, Masayoshi*; Yamashita, Shinichiro
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no abstracts in English
Yamashita, Shinichiro; Yano, Yasuhide; Endo, Masaki*; Sakaguchi, Norihito*; Watanabe, Seiichi*; Miyagi, Masanori*; Sato, Shinya*; Sato, Yutaka*; Kokawa, Hiroyuki*; Kawai, Masayoshi*
no journal, ,
no abstracts in English
Yano, Yasuhide; Yamashita, Shinichiro; Endo, Masaki*; Sakaguchi, Norihito*; Watanabe, Seiichi*; Miyagi, Masanori*; Oyamada, Tetsuya*; Sato, Shinya*; Sato, Yutaka*; Kokawa, Hiroyuki*; et al.
no journal, ,
no abstracts in English
Saito, Shigeru; Kikuchi, Kenji; Hamaguchi, Dai; Tezuka, Masao; Miyagi, Masanori*; Kokawa, Hiroyuki*
no journal, ,
no abstracts in English
Shiota, Yoshinori; Akita, Koichi; Suzuki, Hiroyuki*; Kitazawa, Hideaki*; Yokokawa, Tadaharu*; Koizumi, Yutaka*; Harada, Hiroshi*
no journal, ,
no abstracts in English
Endo, Masaki*; Sakaguchi, Norihito*; Kinoshita, Hiroshi*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Yamashita, Shinichiro; Yano, Yasuhide; Kawai, Masayoshi*
no journal, ,
no abstracts in English
Sakaguchi, Norihito*; Tanikawa, Ryusuke*; Endo, Masaki*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Kawai, Masayoshi*; Yamashita, Shinichiro; Yano, Yasuhide
no journal, ,
no abstracts in English
Sakaguchi, Norihito*; Endo, Masaki*; Kinoshita, Hiroshi*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Yano, Yasuhide; Yamashita, Shinichiro; Kawai, Masayoshi*
no journal, ,
no abstracts in English
Yamashita, Shinichiro; Yano, Yasuhide; Sakaguchi, Norihito*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Kawai, Masayoshi*
no journal, ,
In this study, grain boundary character distribution (GBCD)-optimized Type 316 corresponding austenitic stainless steel has been developed as a nuclear material for next generation energy systems. Some of steel sheets were cold-rolled additionally for making the GBCD-optimized and cold-worked (GBCD+CW) specimens. These specimens, including as GBCD-optimized, were examined tensile strength property, phase stability during high temperature thermal ageing and irradiation property. The GBCD was assessed by orientation imaging microscopy (OIM) and also the microstructure by TEM. The OIM results showed that the average grain sizes and the frequencies of CSL boundaries in the typical specimens were 40-47 
m and more than 70%. Totally considered all experimental results, it was indicated that it is highly possible to develop high performance FBR core material by means of grain boundary engineering.
Sato, Yutaka*; Kokawa, Hiroyuki*; Yano, Yasuhide; Sekio, Yoshihiro
no journal, ,
no abstracts in English
Sekio, Yoshihiro; Yano, Yasuhide; Sato, Yutaka*; Kokawa, Hiroyuki*
no journal, ,
The applicability of friction-stir welding (FSW) which was already put into practical use with nonferrous-metal materials was examined to the 11Cr-ferrite/martensite steel (PNC-FMS) wrapper material in order to improve the welding performance of fast reactor core materials. In this research, the effect of FSW on mechanical and microstructural properties of the Stir Zone (SZ) was investigated. From the experimental results, there was no remarkable decrease in tensile property of the SZ as compared with the base material even though the hardness of the SZ increased due to the influence of very fine grains. This suggests that a post weld heat treatment which was required on the conventional fusion welding might be unnecessary. This study is the result of "Friction stir welding of the wrapper tube materials for Na fast reactors" carried out under the Strategic Promotion Program for Basic Nuclear Research by the Ministry of Education, Culture, Sports, Science and Technology of Japan.
Sato, Yutaka*; Kokawa, Hiroyuki*; Yano, Yasuhide; Sekio, Yoshihiro
no journal, ,
no abstracts in English
Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Shibayama, Tamaki*; Watanabe, Seiichi*; Tokita, Shun*; Fujii, Hiromichi*; Sato, Yutaka*; Kokawa, Hiroyuki*
no journal, ,
In order to improve ductility loss by helium embrittlement (or grain boundary embrittlement) induced under high temperature and neutron irradiation dose in nickel alloys which are expected to have high-temperature phase stability under non-irradiation, the grain boundary engineering was applied for NIMONIC PE16 to enhance the grain boundary strength. And, its high temperature tensile properties under non-irradiation were investigated as the first approach. As a result, the temperature dependence of the yield stress in the grain boundary engineered (GBE) PE16 was similar to that in NIMINIC PE16, but the yield stress was slightly lower and the uniform elongation was slightly higher at each temperature in GBE PE16 comparing to NIMINIC PE16. This would be caused by grain coarsening due to some heat treatments. If the gain size of GBE PE16 is optimized, tensile properties of GBE PE16 would be the same or more than that of NIMONIC PE16.
Yamashita, Shinichiro; Sekio, Yoshihiro; Sakaguchi, Norihito*; Shibayama, Tamaki*; Watanabe, Seiichi*; Kokawa, Hiroyuki*
no journal, ,
Recent grain boundary structure studies have shown that optimal distribution of a high frequency of coincidence site lattice boundaries and consequent discontinuity of random boundary network in the material is one of very effective methods to enhance the intergranular corrosion resistance. This advantageous property, one of important ones for structural material of nuclear reactor, can be obtained through simple thermomechanical treatment process without any change of original chemical composition. In this study, grain boundary character distribution(GBCD)-optimized Ni-based alloy (PE16) has been developed as a prospective high-performance nuclear reactor material by grain boundary engineering processing, and then tensile behavior of GBCD-optimized Ni-based alloy was investigated to evaluate the effect of grain boundary engineering processing on mechanical property. The result of tensile test at room temperature showed that tensile strength of GBCD-optimized PE16 was somewhat lower than that of as-received PE16. However, no significant change was confirmed in elongation property. Details on tensile behavior analyses would be discussed in the conference.
