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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：117 Percentile：97.49(Materials Science, Multidisciplinary)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 
3(111) and fcc Al(Cu) 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.
Kadoyoshi, Tomoko; Kaburaki, Hideo; Shimizu, Futoshi; Kimizuka, Hajime*; Jitsukawa, Shiro; Li, J.*
Acta Materialia, 55(9), p.3073 - 3080, 2007/05
Times Cited Count：61 Percentile：90.89(Materials Science, Multidisciplinary)Critical conditions have been determined for intrinsic transformation of a vacancy Frank loop into a stacking fault tetrahedron in a face centered cubic metal by the molecular dynamics method. We found that a stacking fault tetrahedron can be formed from the scalene hexagonal vacancy Frank loops of wide range of sizes due to the dissociation of dislocations. We have also found atomistically the dynamical process in which vacancy and interstitial faulted Frank loops transform into perfect loops by the application of the external shear stress or by raising the temperature. We have determined numerically the critical shear stress and temperature for the initiation of unfaulting. The simulation results clearly unveiled the important role of temperature in the unfaulting mechanism of an interstitial Frank loop.
Shimizu, Futoshi; Kadoyoshi, Tomoko; Kaburaki, Hideo; Yamagishi, Nobuhiro*; Hasegawa, Yukihiro*; Higuchi, Kenji
Keisan Kogaku Koenkai Rombunshu, 8(2), p.801 - 804, 2003/05
no abstracts in English
Itakura, Mitsuhiro; Kadoyoshi, Tomoko*; Kaburaki, Hideo; Jitsukawa, Shiro
no journal, ,
Molecular dynamics and quasi-two dimensional dislocation dynamics simulations have been performed to find the hardening mechanism of FCC metals due to irradiation. The focus of this simulation has been placed on the effects of the dissociation of a dislocation in FCC metals and of density, distribution, and strength of pinning centers on the stress-strain relation. Molecular dynamics method is applied to find the behavior of the interaction of an edge or a screw dislocation with a pinning center, such as a rigid sphere or irradiation-induced hexagonal interstitial cluster, and to measure its pinning strength by deriving the stress-strain relation.
Kaburaki, Hideo; Kadoyoshi, Tomoko; Itakura, Mitsuhiro; Yamaguchi, Masatake; Suzudo, Tomoaki; Jitsukawa, Shiro
no journal, ,
Recent results on the microscopic simulations on the hardening and embrittlement of materials have been reviewed. The topics include the grain boundary embrittlement by the first principle calculations, unfaulting process of vacancy and interstitial clusters by the molecular dynamics, and dislocation pinning mechanism on the hardening by the molecular dynamics and two-dimensional dislocation dynamics.
Itakura, Mitsuhiro; Kadoyoshi, Tomoko; Kaburaki, Hideo
no journal, ,
Molecular dynamics and quasi-two dimensional dislocation dynamics simulations have been performed to find the Orowan hardening mechanism of a mixed dislocation in FCC metals. The effects of the dissociation of a dislocation in FCC metals on the stress-strain relation, in particular, the pinning strength of a leading and trailing partial dislocation, have been determined by these methods. We focus on studying the pinning behavior of a mixed dislocation, including an edge and a screw dislocation, as a function of the length between the Orowan pinning sites.
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.
Itakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake; Kadoyoshi, Tomoko
no journal, ,
To identify the mechanism of grain boundary crack propagation induced by hydrogen embrittlement, we have constructed a simulation model which couples hydrogen segregation and crack propagation. Using parameters obtained from quantum mechanical calculation, we obtained results which is consistent with experiments; The critical stress reduces to two third by hydrogen segregation, and it further reduces to one third for delayed fracture.
Kaburaki, Hideo; Yamaguchi, Masatake; Itakura, Mitsuhiro; Ebihara, Kenichi; Kadoyoshi, Tomoko; Suzudo, Tomoaki
no journal, ,
no abstracts in English
Kadoyoshi, Tomoko; Kaburaki, Hideo; Itakura, Mitsuhiro; Yamaguchi, Masatake
no journal, ,
Yamaguchi, Masatake; Ebihara, Kenichi; Itakura, Mitsuhiro; Suzudo, Tomoaki; Kaburaki, Hideo; Kadoyoshi, Tomoko*
no journal, ,
From first-principles, we calculated the trapping energy of hydrogen atoms in bcc Fe Sigma 3 (111) and fcc Al (Cu) Sigma 5 (012) symmetrical tilt grain boundaries and on the fracture surfaces with varying the trapping density of hydrogen. For Fe case, 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. For Al case, we find a similar trend as Fe case. For Cu case, on the other hand, the decrease in the cohesive energy of the grain boundary by the hydrogen trapping is much smaller than that for Fe and Al cases. This is because the trapping density of hydrogen atoms is very low in the Cu grain boundary and its fracture surface. The hydrogen trapping may cause brittle fracture in the grain boundaries for Fe and Al.
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.
Kadoyoshi, Tomoko; Kaburaki, Hideo; Itakura, Mitsuhiro; Yamaguchi, Masatake
no journal, ,
Kaburaki, Hideo; Kadoyoshi, Tomoko; Itakura, Mitsuhiro; Yamaguchi, Masatake
no journal, ,
-iron single crystal containing a grain boundary; Molecular dynamics simulationKaburaki, 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.
