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Journal Articles

First-principles study on the grain boundary embrittlement of metals by solute segregation, 2; Metal(Fe, Al, Cu)-Hydrogen (H) systems

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

Metallurgical and Materials Transactions A, 42(2), p.330 - 339, 2011/02

 Times Cited Count:111 Percentile:97.46(Materials Science, Multidisciplinary)

Journal Articles

A Numerical study on the validity of the local equilibrium hypothesis in modeling hydrogen thermal desorption spectra

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

ISIJ International, 49(12), p.1907 - 1913, 2009/12

 Times Cited Count:29 Percentile:78.15(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.

Journal Articles

First-principles study on the decohesion of grain boundary by hydrogen trapping in Aluminum and other metals

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

Proceedings of 18th International Symposium on Processing and Fabrication of Advanced Materials (PFAM-18), p.65 - 74, 2009/12

Generally speaking, the reduction of surface energy by hydrogen trapping is not considered as a key factor in the mechanism of hydrogen embrittlement of metals. This is because it is not known how much hydrogen atoms can be trapped at grain boundaries of metals and how much the cohesive energy (work of fracture) of the grain boundary can be reduced by the hydrogen trapping. From first-principles, we calculated the cohesive energy of bcc Fe $$Sigma$$3(111) and fcc Al(Cu) $$Sigma$$5(012) symmetrical tilt grain boundaries with varying the trapping density of hydrogen. We found that the cohesive energy of Fe, Al and Cu grain boundaries can be significantly reduced by the hydrogen trapping; it indicates that the reduction of surface energy can cause the hydrogen embrittlement in all Fe, Al, and Cu grain boundaries.

Journal Articles

The Mechanism of hydrogen embrittlement due to the reduction in surface energy; A First-principles study

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

Nihon Kikai Gakkai Dai-21-Kai Keisan Rikigaku Koenkai Rombunshu (CD-ROM), p.35 - 36, 2008/11

no abstracts in English

Journal Articles

Modeling of hydrogen thermal desorption profile of pure iron and eutectoid steel

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:35.76(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.)

Oral presentation

Simulation of separation of hydrogen desorption peak for grain boundary

Ebihara, Kenichi; Yamaguchi, Masatake; Suzudo, Tomoaki; Kaburaki, Hideo; Takai, Kenichi*

no journal, , 

The kind and the amount of defects in steel, that trap hydrogen, can be estimated from peaks in the hydrogen desorption profile obtained from thermal desorption analysis. We developed a numerical model which can simulate the desorption profiles for pure iron and eutectoid steel. Studying the mechanism of intergranular cracking by hydrogen embrittlement, in this presentation, we talk of the simulation of separating the peak for grain boundary from that for dislocation using the numerical model incorporating the binding energy of grain boundary which is obtained from the first-principles calculation.

Oral presentation

First-principles calculations of gran boundary cohesive energy; Embrittlement effect of hydrogen

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

no journal, , 

no abstracts in English

Oral presentation

Modeling of the mechanism of delayed fracture initiation

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

no journal, , 

Hydrogen greatly changes mechanical properties of metals, and, in particular, causes delayed fracture of high strength steels. Hydrogen-induced embrittlement has been known for almost a century, and, yet its mechanism is not exactly identified. We concentrated on studying the intergranular brittle fracture at high hydrogen content, using numerical methods, such as first principles calculation, cohesive zone model, and continuum model. We show from the simulation results that a hydrogen-induced intergranular fracture occurs due to the weakening of atomic bonds at the grain boundary region.

Oral presentation

Hydrogen embrittlement of a grain boundary in alpha-iron; A Molecular dynamics study

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

no journal, , 

Oral presentation

First-principles calculations of grain boundary cohesive energy, 2; Hydrogen embrittlement of iron

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

no journal, , 

It is not known in detail how much hydrogen atoms can be trapped in grain boundaries of metals and how much the cohesive energy (work of fracture) of grain boundary is decreased by the hydrogen trapping. From first-principles, we calculated the trapping energy of hydrogen atoms in bcc Fe Sigma 3 (111) symmetrical tilt grain boundaries and on the fracture surfaces with varying the trapping density of hydrogen. We find that hydrogen atoms can be trapped up to a high concentration in the grain boundaries and on the fracture surfaces for Fe. We also find that the trapping energy on the surface is significantly larger than that in the grain boundary. The cohesive energy of the grain boundary is decreased by hydrogen trapping by about 30% at most. Moreover, the cohesive energy can be decreased by about 70% at most if hydrogen in solid solution state moves quickly and then adsorbs onto the newly generated fracture surfaces.

Oral presentation

A Molecular dynamics study on hydrogen embrittlement of a grain boundary in alpha-iron

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

no journal, , 

Oral presentation

Molecular dynamics simulation on the grain boundary embrittlement of iron crystal

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

no journal, , 

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