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Yano, Yasuhide; Tanno, Takashi; Kaito, Takeji; Otsuka, Satoshi; Onuma, Masato*; Nakashima, Hideharu*; Toyama, Takeshi*
no journal, ,
no abstracts in English
Oka, Hiroshi*; Hashimoto, Naoyuki*; Tanno, Takashi; Yano, Yasuhide; Otsuka, Satoshi; Kaito, Takeji
no journal, ,
The effect of nitrogen concentration on microstructure and high temperature creep strength of 9Cr-ODS ferritic/martensitic steel was investigated. The results showed that the tensile strength and high temperature creep strength decreased with increasing nitrogen concentration. The microstructural analysis suggests that the non-uniform dispersion of Y-Ti-O particles due to the increase in nitrogen concentration may have been the cause of the decrease in high temperature creep strength. The non-uniform dispersion of Y-Ti-O particles is probably the result of the consumption of Ti by the formation of Ti nitrides, which weakened its refinement effect on the nano-sized oxide particles.
Otsuka, Satoshi; Onuma, Masato*; Mitsuhara, Masatoshi*; Nakashima, Hideharu*; Toyama, Takeshi*; Yano, Yasuhide; Hashidate, Ryuta; Kaito, Takeji
no journal, ,
Fuel cladding tube takes on an important function in fuel safety by confining the fission products in fuel element and keeping the coolant flow path in fuel assembly. Oxide dispersion strengthened (ODS) steels have excellent mechanical strength and dimensional stability. The application of ODS steel for fuel cladding tube of sodium-cooled fast reactor (SFR) can restrain the rupture and excessive deformation of fuel pin, thus enhancing the fuel safety. For implementation of ODS steel cladding tube to the driver fuel of SFR, it is essential to correctly understand its irradiation performance, and improve the reliability of structural integrity under operation. This study carries out the research towards the development of new technique efficiently evaluating irradiation properties of ODS steel on the basis of correlation between mechanical strength and microstructure peculiar to ODS steels, which has been proved by the authors.
Imagawa, Yuya; Hashidate, Ryuta; Onizawa, Takashi; Kato, Shoichi; Otsuka, Satoshi; Onuma, Masato*; Nakashima, Hideharu*; Toyama, Takeshi*
no journal, ,
Oxide dispersion strengthened (ODS) steel, which has high strength at high to very high temperatures by uniform dispersion of nano-sized oxide particles with excellent thermal stability, is expected to be applied as a fuel cladding tube material to improve safety in the next generation sodium-cooled fast reactor (SFR). In this study, circumferential creep tests and evaluations of ODS steels at high to very high temperatures were carried out in order to obtain basic data for clarifying the correlation between microstructure and mechanical properties in the temperature range from high temperatures during abnormal transients to very high temperatures during accidents.
Ha, Yoosung; Shimodaira, Masaki; Katsuyama, Jinya
no journal, ,
no abstracts in English
Toyama, Takeshi*; Tanno, Takashi; Yano, Yasuhide; Otsuka, Satoshi; Mitsuhara, Masatoshi*; Nakashima, Hideharu*; Onuma, Masato*
no journal, ,
no abstracts in English
Mitsuhara, Masatoshi*; Kurino, Koichi*; Nakashima, Hideharu*; Yano, Yasuhide; Otsuka, Satoshi; Onuma, Masato*; Toyama, Takeshi*
no journal, ,
no abstracts in English
Yamazaki, Jin*; Onuma, Masato*; Otsuka, Satoshi; Tanno, Takashi; Toyama, Takeshi*; Mitsuhara, Masatoshi*; Nakashima, Hideharu*
no journal, ,
X-ray small angle scattering (SAXS) analysis was carried out in order to evaluate the stability of nano-sized dispersed oxide particles in oxide dispersed strengthened (ODS) steels after creep test. The size of oxide particles was not changed after creep tests at 800
C and below. On the other hand, the size tended to increase in the sampled tested at over 800C. However, the SAXS analysis showed that the nano-sized Y
TiO
oxide particle still existed in the sample after the creep test at 1000C. The result shows that dispersed nano-sized oxide particles in ODS steels have superior stability under creep test at high temperature.
Hayashi, Yusaku*; Ueda, Mitsutoshi*; Kawamura, Kenichi*; Irisawa, Eriko; Komatsu, Atsushi; Kato, Chiaki; Okubo, Nariaki
no journal, ,
It is necessary to form a protective oxide film on the surface in order to protect stainless steel from corrosion by liquid LBE at high temperatures. A resistance change type sensor using the reduction/oxidation phenomenon of metal oxides was devised for the oxygen concentration in liquid LBE decreases and the protective oxide film disappears from the stainless steel surface. In this paper, the principle of operation of the sensor was experimentally confirmed and its response was evaluated.
Tsuru, Tomohito; Lobzenko, I.; Yuge, Koretaka*; Aoyagi, Yoshiteru*; Shimokawa, Tomotsugu*; Kubo, Momoji*; Ogata, Shigenobu*
no journal, ,
In the present study, we investigated the short-range order and the core structure of dislocations in body centered cubic (BCC) HEAs using density functional theory (DFT) calculations. Special quasirandom structures (SQS) scheme was employed to mimic randomly-distributed five-component BCC-HEAs with equiatomic fraction. According to the phase stability based on DFT calculations, MoNbTaVW and ZrNbTaTiHf HEAs are taken as the typical cases of energetically stable and unstable BCC-HEAs.
Sato, Yuki*; Abe, Yosuke; Okubo, Kenji*; Tanioka, Takashi*
no journal, ,
Self-interstitial atom (SIA) clusters are produced from collision cascades, after which they escape quickly through one-dimensional (1D) migration, affecting the microstructural evolution in materials. In this study, we examined impurities induced by heat treatment for specimen preparation and their effects on the 1D migration of self-interstitial atom clusters in copper by in situ observations using a high-voltage electron microscopy. The results showed that for high-purity specimens, 1D migration distances were considerably suppressed by a standard heat treatment (cold-rolled, punched-out, and annealed) compared to those without annealing (mechanically polished, and punched-out). On the other hand, for low-purity specimens, where a large amount of residual impurities was intrinsically contained, 1D migration distances were almost same among specimens with and without the heat treatment. The results suggest that not only residual impurities but also impurities induced by the heat treatment affect the 1D migration behavior.
O
irradiated with swift heavy ions; Fluence dependenceIshikawa, Norito; Kondo, Keietsu; Fujimura, Yuki; Ogawa, Hiroaki
no journal, ,
AlO single crystals are irradiated with MeV Au ion beams, and the samples are analyzed with EBSD technique. As a result, strain increased with increasing fluence. Especially, decrease in lattice parameter is observed in the direction perpendicular to the irradiation direction.
Hashimoto, Naoyuki*; Isobe, Shigehito*; Oka, Hiroshi*; Hayashi, Shigenari*; Ueda, Mikito*; Yamashita, Shinichiro; Itakura, Mitsuhiro; Tsuru, Tomohito
no journal, ,
Owing to the reduced defects, low cost, and high efficiency, the additive manufacturing (AM) technique has attracted increasingly attention and has been applied in high-entropy alloys (HEAs) in recent years. For the purpose of creating new materials which show no radiation damage or prompt recovery of radiation damage, we launched a new program in which additive-manufactured HEAs are target materials and their fundamental properties are under investigation. In this presentation, we reported the some of new test results which are conducted in the program.
Nakabachi, Kaito*; Yokoyama, Kenichi*; Ishijima, Yasuhiro; Ueno, Fumiyoshi; Abe, Hitoshi
no journal, ,
To investigate the effects of strain and thermal aging on hydrogen embrittlement of Ta, tensile tests and internal friction measurements were carried out on cold rolled Ta after hydrogen charging and thermal aging. As a result, the internal friction increased with cold rolling. The internal friction was further increased by hydrogen charging. However, the internal friction of these specimens decreased after thermal aging. These results suggest that aging causes the annihilation or re-arrangement of defects or a change in the hydrogen trapping. In addition, the ductility of the hydrogen-charged and cold-rolled specimens decreased after thermal aging, suggesting that the change in hydrogen and defect state due to thermal aging affects the mechanical properties.
Suzudo, Tomoaki; Ebihara, Kenichi; Tsuru, Tomohito
no journal, ,
BCC metals are used for various purposes as structural materials, but it is known that they become brittle in the low temperature region and brittleness is promoted by impurities such as hydrogen. It is desirable to properly model and predict the phenomenon, but the mechanism is very complicated and it is not easy to model. Fracture is a macroscopic phenomenon, but it is also a microscopic phenomenon caused by the breakage of interatomic bonds. Therefore, it is necessary to accurately reproduce the atomic arrangement and stress concentration at the crack tip, and to predict the breakage and plastic deformation of the interatomic bond. In this study, to model the cleavage of BCC metals, molecular dynamics simulation was performed for iron as an example. The results showed that cleavage on {100} was the easiest to grow.