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Journal Articles

Numerical modeling of thermal desorption spectra of hydrogen; A Review of thermal desorption models

Ebihara, Kenichi; Kaburaki, Hideo

ISIJ International, 52(2), p.181 - 186, 2012/02

 Times Cited Count:12 Percentile:50.86(Metallurgy & Metallurgical Engineering)

In the study of hydrogen embrittlement, it is indispensable to identify the hydrogen trapping state in steels. The hydrogen thermal desorption profile, which is obtained from the thermal desorption analysis (TDA) and is the relation between temperature and the amount of desorbed hydrogen of a specimen heated at a constant rate, is effective. Since various factors such as the specimen size, the heating rate, the hydrogen diffusion and the trapping effect of defects affect the desorption profile, however, it is necessary to model the process of the hydrogen desorption from the specimen. This paper reviewed the present model which can simulate the desorption profile by categorizing them according to the rate-determining process of the hydrogen desorption. The historical background and the range of validity of the models were also mentioned.

Journal Articles

Evaluation of stress and hydrogen concentration at grain boundary of steels using three-dimensional polycrystalline model

Ebihara, Kenichi; Itakura, Mitsuhiro; Yamaguchi, Masatake; Kaburaki, Hideo; Suzudo, Tomoaki

Progress in Nuclear Science and Technology (Internet), 2, p.38 - 43, 2011/10

The decohesion model in which hydrogen segregating at grain boundaries reduces cohesive energy is considered to explain hydrogen embrittlement. In order to verify the decohesion model, it is necessary to evaluate stress and hydrogen concentration at grain boundaries under experimental conditions. Thus, we calculated the stress and the hydrogen concentration at grain boundaries in the 3-dimensional polycrystalline model generated by the random Voronoi tessellation. The crystallographic anisotropy was given to each grain as a characteristic. As the boundary conditions, data extracted from the results calculated in the notched round-bar specimen model under the tensile test condition was given to the polycrystalline model. As a result, it was found that the evaluated stress does not reach the fracture stress estimated by first-principles calculations. Therefore, it was considered that the initiation of grain boundary fracture needs some factors except the crystallographic anisotropy.

Journal Articles

Evaluation of local stress and local hydrogen concentration at grain boundary using three-dimensional polycrystalline model

Ebihara, Kenichi; Itakura, Mitsuhiro; Yamaguchi, Masatake; Kaburaki, Hideo; Suzudo, Tomoaki

Proceedings of Joint International Conference of 7th Supercomputing in Nuclear Application and 3rd Monte Carlo (SNA + MC 2010) (USB Flash Drive), 6 Pages, 2010/10

The decohesion model in which hydrogen segregating at grain boundaries reduces their strength is considered to explain hydrogen embrittlement of steels. Therefore in order to understand hydrogen embrittlement from this model, stress and hydrogen concentration at grain boundaries need be evaluated under the fracture condition for tensile test specimens. From this consideration, we evaluated the stress and the hydrogen concentration at grain boundaries in the three-dimensional polycrystalline model which was generated by Voronoi tessellation. The different crystallographic orientation was given to each grain. Extracted data from the calculation in the notched round-bar specimen model under the tensile test condition was given to the polycrystalline model as the boundary condition. As a result, it was found that the valuated stress does not reach the fracture stress which was estimated under the condition of the evaluated hydrogen concentration by first principles calculation.

Journal Articles

High-energy total reflection X-ray photoelectron spectroscopy for polished iron surface

Nagoshi, Masayasu*; Kawano, Takashi*; Makiishi, Noriko*; Baba, Yuji; Kobayashi, Katsumi*

Surface and Interface Analysis, 40(3-4), p.738 - 740, 2008/04

 Times Cited Count:3 Percentile:91.86(Chemistry, Physical)

Grazing incidence X-ray photoelectron spectroscopy (XPS) has been applied to mirror-polished stainless steel sheets and Si-wafer using incident X-ray with high energy from synchrotron radiation. Monochromatized X-ray with the energy of 1.8 keV to 3.6 keV was irradiated to the sample surfaces with various incident angles. Total reflection condition with the high-energy incident X-ray provides us X-ray photoelectron spectra having remarkably low background intensity. The results will be compared with background calculations in previous researches and discussed in terms of the penetration depth of X-ray and inelastic mean free path of photoelectrons. We also discuss the depth information of the obtained spectra.

Oral presentation

First-principles study on the grain boundary embrittlement of metals by hydrogen

Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Suzudo, Tomoaki; Kaburaki, Hideo

no journal, , 

no abstracts in English

Oral presentation

Brittle to ductile transition in the fracture process of an $$alpha$$-iron single crystal containing a grain boundary; Molecular dynamics simulation

Kaburaki, Hideo; Kadoyoshi, Tomoko; Itakura, Mitsuhiro; Yamaguchi, Masatake

no journal, , 

Many single crystal metals intrinsically exhibit brittle-to-ductile transition (BDT) as a function of temperature and strain rate. These materials are generally brittle at low temperatures or high strain rates, and become ductile as the temperature rises or the strain rate decreases. Since the atomistic picture of brittle-to-ductile transition is still unknown, we have performed molecular dynamics simulations on the fracture process of iron single crystal by varying the temperature and strain rate in a wide range. From the atomistic results, we have found that the transition point shifts to the higher temperature due to the high strain rate.

Oral presentation

Molecular dynamics simulation on the brittle-ductile transition of BCC iron

Kaburaki, Hideo

no journal, , 

Many single crystal metals, such as BCC iron, intrinsically exhibit brittle-to-ductile transition (BDT) as a function of temperature and strain rate. These materials are generally brittle at low temperatures or high strain rates, and become ductile as the temperature rises or the strain rate decreases. Although there have been many experimental studies on BDT, its mechanism is not clearly identified. We employed the atomistic method, molecular dynamics method, to clarify the mechanism of BDT for BCC iron. We studied the pure iron system containing one grain boundary to realize the BDT. We have found that the BDT temperature is shifted to the higher temperature region, compared to experiment, due to the high strain rate used in the molecular dynamics method.

Oral presentation

Numerical estimation of applicability of Choo and Lee's method for evaluating detrapping activation energy

Ebihara, Kenichi; Kaburaki, Hideo; Takai, Kenichi*

no journal, , 

In order to understand the mechanism of hydrogen embrittlement of steels, it is necessary to evaluate the binding energy between a lattice defect and a hydrogen atom which influences the hydrogen trapping state in steels. Since the binding energy can be evaluated theoretically and experimentally due to recent development of technologies, it may become possible to estimate the binding energy in practical steels. Because the Choo-Lee method for estimating the binding energy from the thermal hydrogen desorption analysis is restricted to the case of the thermal-detrapping-determining hydrogen desorption process, the applicability of the Choo-Lee method was studied numerically. As a result, it was found that the restriction of the Choo-Lee method is relaxed when the hydrogen-charged specimen is held below the temperature at which the hydrogen desorption starts.

Oral presentation

Mobile effect of hydrogen in hydrogen-induced intergranular embrittlement of iron; First-principles calculations

Yamaguchi, Masatake; Kameda, Jun*; Ebihara, Kenichi; Itakura, Mitsuhiro; Kaburaki, Hideo

no journal, , 

no abstracts in English

Oral presentation

Dislocation emission from the transformed crack tip of bcc iron bulk nanocrystal; Molecular dynamics simulation

Kaburaki, Hideo; Itakura, Mitsuhiro; Yamaguchi, Masatake

no journal, , 

no abstracts in English

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