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Ebihara, Kenichi; Sekine, Daiki*; Sakiyama, Yuji*; Takahashi, Jun*; Takai, Kenichi*; Omura, Tomohiko*
International Journal of Hydrogen Energy, 48(79), p.30949 - 30962, 2023/09
Times Cited Count：0 Percentile：0.00(Chemistry, Physical)To understand hydrogen embrittlement (HE), which is one of the stress corrosion cracking of steel materials, it is necessary to know the H distribution in steel, which can be effectively interpreted by numerical simulation of thermal desorption spectra. In weld metals and TRIP steels, residual austenite significantly influences the spectra, but a clear H distribution is not well known. In this study, an originally coded two-dimensional model was used to numerically simulate the previously reported spectra of high-carbon ferritic-austenitic duplex stainless steels, and it was found that H is mainly trapped at the carbide surface when the amount of H in the steel is low and at the duplex interface when the amount of H is high. It was also found that the thickness dependence of the H desorption peak for the interface trap site is caused by a different reason than the conventional one.
Saito, Kei*; Hirade, Tetsuya; Takai, Kenichi*
Key Engineering Materials, 967, p.11 - 16, 2023/07
Hydrogen-enhanced strain-induced vacancy, one of the defects associated with promising hydrogen embrittlement mechanisms, was validated for tempered martensitic steel showing quasi-cleavage fracture with a tensile strength of 1500 MPa level by slow strain rate tensile test in-situ electrochemical hydrogen charging. The effect of newly formed vacancy-type defects on mechanical properties of tempered martensitic steel was also studied. Combined use of low-temperature thermal desorption spectroscopy (L-TDS) and the tensile test revealed the following three things: (i) hydrogen enhanced the accumulation of vacancy-type defects with plastic straining, (ii) accumulated vacancy-type defects deteriorated the ductility of the tempered martensitic steel after hydrogen release, and (iii) aging in the range from 50
C to 150C after applying given plastic strain with hydrogen charging decreased the amount of newly formed vacancy-type defects, and then resulted in the recovery of the ductility.
Ebihara, Kenichi; Sugiyama, Yuri*; Matsumoto, Ryosuke*; Takai, Kenichi*; Suzudo, Tomoaki
Metallurgical and Materials Transactions A, 52(1), p.257 - 269, 2021/01
Times Cited Count：9 Percentile：41.71(Materials Science, Multidisciplinary)We simulated the thermal desorption spectra of a small-size iron specimen to which was applied during charging with hydrogen atoms using a model incorporating the behavior of vacancies and vacancy clusters. The model considered up to vacancy clusters 
, which is composed of nine vacancies and employed the parameters based on atomistic calculations, including the H trapping energy of vacancies and vacancy clusters that we estimated using the molecular static calculation. As a result, we revealed that the model could, on the whole, reproduced the experimental spectra except two characteristic differences, and also the dependence of the spectra on the aging temperature. By examining the cause of the differences, the possibilities that the diffusion of clusters of 
and 
is slower than the model and that vacancy clusters are generated by applying strain and H charging concurrently were indicated.
Saito, Kei*; Hirade, Tetsuya; Takai, Kenichi*
Metallurgical and Materials Transactions A, 50(11), p.5091 - 5102, 2019/11
Times Cited Count：35 Percentile：84.86(Materials Science, Multidisciplinary)An attempt was made to separate and identify hydrogen peaks desorbed from lattice defects formed by plastic-strain in the presence of hydrogen in tempered martensitic steel showing quasi-cleavage fracture using thermal desorption spectroscopy from a low temperature (L-TDS) and positron annihilation spectroscopy (PAS). The L-TDS results made it possible to separate two peaks, namely, that of the original desorption and also that of new desorption. The PAS results revealed that the new desorption obtained by L-TDS corresponded to vacancy-type defects. Hydrogen enhanced vacancy-type defect concentration, approximately 10
order in terms of atomic ratio, formed within 1.5 mm from the fracture surface, These results indicate that the accumulation of excess vacancy-type defects enhanced by hydrogen in the local region can lead to nanovoid nucleation and coalescence in plastic deformation, resulting in quasi-cleavage fracture of tempered martensitic steel.
Ebihara, Kenichi; Saito, Kei*; Takai, Kenichi*
"Suiso Zeika No Kihon Yoin To Tokusei Hyoka" Kenkyukai Hokokusho, p.57 - 61, 2018/09
no abstracts in English
Ebihara, Kenichi; Saito, Kei*; Takai, Kenichi*
Proceedings of 2016 International Hydrogen Conference (IHC 2016); Materials Performance in Hydrogen Environments, p.470 - 477, 2017/00
For understanding hydrogen (H) embrittlement of steels, it is necessary to infer the state that defects trap H in the steels. Thermal desorption spectra of H obtained by the thermal desorption spectrometry (TDS) are used for inferring such a state. Because the thermal desorption spectra include the influence of experimental conditions and hydrogen diffusion as well as information of the defects trapping H, it is necessary to interpret the spectra using the numerical simulation. In the presentation, we determined the detrapping and the trapping rate constants which are necessary for the simulation from the experimental spectra obtained for plate specimens which is so small that H diffusion is ignorable. Then we confirmed that the model using the obtained rate constants can simulate the spectra of larger cylindrical specimens, so that it was found that the rate constant for small specimens can be used for the simulation of the spectra for specimens of different shape or size.
Ebihara, Kenichi; Saito, Kei*; Takai, Kenichi*
"Suiso Zeika No Kihon Yoin To Tokusei Hyoka Kenkyukai Chukan Hokokukai" Shimposium Yokoshu (USB Flash Drive), p.30 - 35, 2016/09
no abstracts in English
Ebihara, Kenichi; Saito, Kei*; Takai, Kenichi*
"Suiso Zeika No Kihon Yoin, Kaiseki To Hyoka" Shimposium Yokoshu (USB Flash Drive), p.27 - 33, 2015/09
The thermal desorption spectra which reflect the H segregation state can be obtained by heating a specimen including H at a constant rate. However, the simulation of spectra needs to extract information of the H segregation state because spectra is affected by experimental conditions and H diffusion. The detrapping activation energy E
and the pre-exponential factor of detraping rate constant which are simulation parameters are fixed from the data previously reported or by fitting experimental spectra. Instead, we evaluated both of them from the experimental spectra of the specimen in which the H diffusion effect can be ignored, and simulated the spectra using them. As a result, in the case of iron, we could simulate spectra better than by the previous parameters. In the case of tempered martensitic steel, we could simulate spectra by the value obtained by adjusting the evaluated p
along with the evaluated E.
Doshida, Tomoki*; Suzuki, Hiroshi*; Takai, Kenichi*; Hirade, Tetsuya; Oshima, Nagayasu*
NanotechJapan Bulletin (Internet), 8(3), 5 Pages, 2015/07
Studying the creation and time evolution of defects is an important issue for interpreting the hydrogen embrittlement mechanism of steels. We have been studied the relationship between hydrogen embrittlement of high strength steel and lattice defects associated with hydrogen by thermal desorption analysis (TDA) and positron probe microanalyzer (PPMA).
Ebihara, Kenichi; Kaburaki, Hideo; Takai, Kenichi*
Zairyo To Purosesu (CD-ROM), 27(1), P. 418, 2014/03
In order to understand the mechanism of hydrogen embrittlement, identifying the state of hydrogen trapped by defects in steels is dispensable. In the identification of the hydrogen trapping state, thermal desorption profiles of hydrogen obtained in the thermal desorption analysis of steel specimens are widely used, and need to be analyzed using the numerical model because they include the effect of the specimen size and the experimental conditions as well as the effect of defects. The prefactor of detrap rate in the model is previously used as a fitting parameter. In the presentation, the influence of specimen size on the identification of the prefactor was examined numerically. As a result, in the specimens of pure iron and martensite steels whose size is larger than 0.3 mm, the accuracy of the identification rapidly drops. In addition, according to the influence of the prefactor on the desorption profile, it is possible to identify the order of magnitude of the prefactor.
Ebihara, Kenichi; Kaburaki, Hideo; Takai, Kenichi*
Proceedings of 2012 International Hydrogen Conference; Hydrogen-Materials Interactions, p.553 - 561, 2014/02
The crack causing hydrogen embrittlement is observed in steels as the structural material. Accurate evaluation of hydrogen detrapping activation energy, which represents the binding strength between hydrogen atoms and the lattice defects, is crucial to the understanding of the mechanism of hydrogen embrittlement in steels. The Choo and Lee's method, which experimentally evaluates the detrapping energy from the hydrogen thermal desorption profile, should be scrutinized, because this method neglects the hydrogen diffusion in the specimen. By their method, we have evaluated detrapping activation energies from the experimental desorption profiles for pure iron, and also from that simulated by the 1D reaction-diffusion equation. We found that their method underestimates the detrapping energies as the specimen size is large. We also found that this dependence on the specimen size is caused by the degradation of the desorption peak of the detrapping process by the diffusion process.
Doshida, Tomoki*; Suzuki, Hiroshi*; Takai, Kenichi*; Oshima, Nagayasu*; Hirade, Tetsuya
ISIJ International, 52(2), p.198 - 207, 2012/02
Times Cited Count：68 Percentile：92.78(Metallurgy & Metallurgical Engineering)Hydrogen behavior and hydrogen-enhanced lattice defect formation under elastic stress of tempered martensitic steel were clarified with respect to dislocations and vacancies by thermal desorption analysis (TDA) using hydrogen as a probe of defects and a positron probe microanalyzer (PPMA). The relationship between hydrogen embrittlement and lattice defects associated with hydrogen was also investigated. The amount of lattice defects increased gradually with increasing time of applied stress. The specimen fractured under elastic stress. The enhanced vacancies due to interactions between dislocations and hydrogen under elastic stress directly caused ductility loss. Even though hydrogen was completely removed by degassing the vacancies remain. Besides hydrogen content and applied stress, the time of formation and accumulation of vacancies are also concluded to be important factors causing hydrogen embrittlement.
Ebihara, Kenichi; Kaburaki, Hideo; Suzudo, Tomoaki; Takai, Kenichi*
ISIJ International, 49(12), p.1907 - 1913, 2009/12
Times Cited Count：33 Percentile：78.97(Metallurgy & Metallurgical Engineering)We present a systematic benchmark study on different numerical models for analyzing hydrogen thermal desorption spectra, by focusing on the adoption of the local equilibrium hypothesis in these models. We find that the direct numerical method of the full set of the extended mass conservation equations is only able to predict the experimental behavior of thermal desorption spectra for pure iron in the thin specimen limit, while other models incorporating the local equilibrium hypothesis fail to predict this behavior.
Ebihara, Kenichi; Suzudo, Tomoaki; Kaburaki, Hideo; Takai, Kenichi*; Takebayashi, Shigeto*
Tetsu To Hagane, 94(11), p.62 - 71, 2008/11
Times Cited Count：5 Percentile：34.93(Metallurgy & Metallurgical Engineering)We have developed a numerical model to simulate the hydrogen desorption profiles for pure iron and eutectoid steel, which is obtained in thermal desorption analysis (TDA). Our model incorporates the equation of McNabb and Foster without the hydrogen diffusion term combined with the Oriani's local equilibrium theory. It is found that the present numerical model successfully simulates the hydrogen desorption profile using the concentration of hydrogen trapping sites which is inferred from experiments both for pure iron and for eutectoid steel. We further verify the model by discussing the trapping site concentration and the effect of hydrogen diffusion. (Although this paper is similar to [ISIJ International 47(2007)1131], the process of numerical calculation is described in more detail.)
Ebihara, Kenichi; Suzudo, Tomoaki; Kaburaki, Hideo; Takai, Kenichi*; Takebayashi, Shigeto*
ISIJ International, 47(8), p.1131 - 1140, 2007/08
Times Cited Count：22 Percentile：71.12(Metallurgy & Metallurgical Engineering)In thermal desorption analysis(TDA), a hydrogen desorption profile, which represents the relation between the amount of desorbed hydrogen and specimen temperature, can be obtained by heating the specimen including hydrogen with a certain rate. We can estimate the amount of sites trapping hydrogen in the specimen, such as vacancies, dislocations and interfaces of phases from the profile. We have developed a numerical model to simulate the hydrogen desorption profiles for pure iron and eutectoid steel. Our model incorporates the equation of McNabb and Foster, which is a kind of rate equation, without the hydrogen diffusion term combined with the Oriani's local equilibrium theory, which describes the hydrogen trapping state. It is found that the present numerical model successfully simulates the profile both for pure iron and for eutectoid steel. We further verify the model by discussing the trapping site concentration and the effect of hydrogen diffusion.
Wada, Yuki; Mitomo, Hiroshi*; Kasuya, Kenichi*; Nagasawa, Naotsugu; Seko, Noriaki; Katakai, Akio; Tamada, Masao
Journal of Applied Polymer Science, 101(6), p.3856 - 3861, 2006/09
Times Cited Count：22 Percentile：54.20(Polymer Science)Radiation-induced graft polymerization of acrylic acid (AAc) on the surface of poly(3-hydroxybutyric acid) (PHB) film was carried out by applying pre-irradiation techniques. The PHB films grafted with AAc (PHB-g-AAc) possessed a degree of grafting higher than 5% have completely lost the enzymatic degradability. The enzymatic degradability of the grafted film was recovered by remolding. And the highest enzymatic degradation rate was observed to grafted films with AAc 10% of degree. Difference of enzymatic degradability of PHB-g-AAc film was caused by decrement of amount of enzyme contact and decrement of crystallinity of PHB by remolding.
Takahashi, Masato; Magara, Masaaki; Sakurai, Satoshi; Kurosawa, Setsumi; Esaka, Fumitaka; Taguchi, Takuji; Takai, Konomi; Fukuyama, Hiroyasu; Lee, C. G.; Yasuda, Kenichiro; et al.
Dai-23-Kai Kaku Busshitsu Kanri Gakkai Nihon Shibu Nenji Taikai Rombunshu, 8 Pages, 2002/09
Based on the strengthen safeguard program of the IAEA to detect undeclared nuclear activities, the method of precise and accurate isotope ratio determination for uranium and plutonium in the environmental samples (cotton swipes) has been developed at JAERI. The samples should be treated in clean environment in order to secure the analytical reliability by eliminating external contamination from the samples containing trace amount of uranium and plutonium. Since the measurement by ICP-MS is favorable to bulk analysis from view points of analytical capacity and operation simplicity, we have studied sample preparation procedures for the trace amount of uranium and plutonium to be applied to ICP-MS. Up to the present, interfering factors involved during analytical processes and the ICP-MS measurement of uranium and plutonium were examined. As a result, uranium and plutonium isotope measurement more than 100 pg and 100 fg, respectively, became possible at JAERI clean facility. At presentation, other progress in the development will be reported.
Esaka, Fumitaka; Magara, Masaaki; Hanzawa, Yukiko; Sakurai, Satoshi; Taguchi, Takuji; Takai, Konomi; Sakakibara, Takaaki; Kurosawa, Setsumi; Takahashi, Masato; Yasuda, Kenichiro; et al.
Dai-22-Kai Kaku Busshitsu Kanri Gakkai Nihon Shibu Nenji Taikai Rombunshu, 8 Pages, 2001/11
no abstracts in English
Jiang, L.*; O'Rourke, B. E.*; Harada, Yoshihisa*; Takatsu, Shuhei*; Ito, Kenji*; Okubo, Masataka*; Hirade, Tetsuya; Uedono, Akira*; Suzuki, Ryoichi*; Takai, Kenichi*; et al.
no journal, ,
We are studying the depth dependence of the density of the defects induced by the electrical discharge machining (EDM) in SUS316L, using the electron probe microanalysis (EPMA), Positron annihilation lifetime spectroscopy (PALS) and X-ray diffraction (XRD). EPMA results show a large change in the composition over the first 10 
m. This layer can be assumed to correspond to the recast layer. PALS and XRD results suggest a defect layer with a thickness of around 50 m. This depth can be assumed to correspond to the heat affected zone where dislocations and vacancy clusters exists. For PALS (and other methods) analysis, it is recommended to remove the topmost 100 m of the samples by chemical polishing after EDM.
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dual phase steels using numerical simulationEbihara, Kenichi; Sekine, Daiki*; Takai, Kenichi*
no journal, ,
no abstracts in English
