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Journal Articles

Analyzing the cross slip motion of screw dislocations at finite temperatures in body-centered-cubic metals; Molecular statics and dynamics studies

Suzudo, Tomoaki; Onitsuka, Takashi*; Fukumoto, Kenichi*

Modelling and Simulation in Materials Science and Engineering, 27(6), p.064001_1 - 064001_15, 2019/08

 Times Cited Count:5 Percentile:36.84(Materials Science, Multidisciplinary)

Plasticity of body-centered-cubic (BCC) metals at low temperatures is determined by screw dislocation kinetics. Because the core of screw dislocation in these metals has non-planar structure, its motion is complex and unpredictable. For example, although density functional theory (DFT) predicts slip on a { 110 } plane, the actual slip plane at elevated temperatures departs from the prediction, its mechanism having been a mystery for decades. Here we conduct a series of molecular dynamics simulations to track the screw dislocation motion and successfully reproduced the transition of the slip plane. We then devised an algorithm to scrutinize the activation of dislocation jump over the Peierls barrier and discovered the possible origin of this unexpected phenomenon, i.e., a large fluctuation leads to the kink-pair nucleation for the cross-slip jump without transition of dislocation core structure.

Journal Articles

Research of estimation method of thermal aging embrittlement on cast austenitic stainless steel

Abe, Teruyoshi; Nogiwa, Kimihiro*; Onitsuka, Takashi*; Nakamura, Takahisa; Sakakibara, Yasuhide

E-Journal of Advanced Maintenance (Internet), 6(4), p.146 - 152, 2015/02

Thermal embrittlement of cast austenitic stainless steel components from the decommissioned advanced thermal prototype reactor Fugen has been characterized. Cast stainless steel materials were obtained from recirculation pump casing. The actual time at temperature for the materials was 138,000 h at 275$$^{circ}$$C. The "Fugen" material show modest decrease in Charpy-impact properties and a small increase in micro-Vickers hardness in ferrite phase because of thermal aging at relatively low service temperatures. The fracture toughness prediction method (H3T model) predicts slightly lower values for Charpy-impact energy obtained from the Fugen material. The results from microstructural analysis suggest that the prediction method have the potential to provide higher accuracy by considerations of the activation energy for embrittlement at low service temperatures.

Journal Articles

Influence of thermal aging on cast stainless steels used in JAEA's nuclear reactor Fugen

Nogiwa, Kimihiro; Onitsuka, Takashi; Abe, Teruyoshi; Sakakibara, Yasuhide; Horie, Kaoru; Nakamura, Takahisa

Journal of Nuclear Science and Technology, 50(9), p.883 - 890, 2013/09

 Times Cited Count:2 Percentile:77.96(Nuclear Science & Technology)

The degree of influence of thermal aging on cast stainless steels over a protracted time at low temperatures was investigated by means of a toughness test and microstructural characterization performed on components dismantled from the advanced thermal proto-type reactor "Fugen". The thermal embrittlement mechanism was examined using data obtained dismantled from the materials that had aged on site. The results of a Charpy impact test and microstructural characterization performed using 3DAP analysis reveal early signs of a thermal aging effect over a protracted period at low temperatures corresponding boiling-water reactor (BWR).

Oral presentation

Radiation hardening in Fe-Ni base low alloy

Onitsuka, Takashi; Ando, Masami; Jitsukawa, Shiro; Iwai, Takeo*

no journal, , 

no abstracts in English

Oral presentation

MD/RT analysis on microstructural evolution during charged particle irradiation in martensitic and austenitc steels at temperatures $$<$$ 673 K

Abe, Yosuke; Onitsuka, Takashi; Ando, Masami; Okubo, Nariaki; Jitsukawa, Shiro

no journal, , 

Fe ion-beam irradiation at 5MeV and electron beam irradiation at 1MeV (in-situ observation with a High Voltage Electron Microscope) have been performed to damage levels up to 10 displacements per atom at temperatures ranging between ambient temperature and 673K. Results were qualitatively agreed with those obtained by the fission reactor irradiation experiments. Microstructural change has been analyzed by computational simulation technique with molecular dynamics and rate theory models. Damage level and temperature dependence of size and number density of defect clusters obtained by calculation with parameters of point defect mobility, defect cluster mobility, sink strength, temperature and damage rate are compared with results by transmission electron microscopy on irradiated martensitic and austenitic steels. Significance of the mobility and sink strength of defect clusters is discussed.

Oral presentation

Influence of thermal aging on cast duplex stainless steels in Fugen served materials

Nogiwa, Kimihiro; Onitsuka, Takashi; Abe, Teruyoshi; Sakakibara, Yasuhide; Nakamura, Takahisa; Horie, Kaoru

no journal, , 

no abstracts in English

Oral presentation

Study of thermal ageing behaviour of duplex stainless steels by positron annihilation lifetime technique

Onitsuka, Takashi; Nogiwa, Kimihiro; Abe, Teruyoshi; Sakakibara, Yasuhide; Nakamura, Takahisa; Horie, Kaoru

no journal, , 

no abstracts in English

Oral presentation

Study of thermal ageing behaviour of duplex stainless steels by positron annihilation lifetime spectroscopy

Onitsuka, Takashi; Nogiwa, Kimihiro; Abe, Teruyoshi; Sakakibara, Yasuhide; Nakamura, Takahisa; Horie, Kaoru

no journal, , 

no abstracts in English

Oral presentation

Research of estimation method of thermal aging embrittlement on cast austenitic stainless steel

Nogiwa, Kimihiro; Onitsuka, Takashi; Abe, Teruyoshi; Sakakibara, Yasuhide; Nakamura, Takahisa

no journal, , 

Thermal embrittlement of cast austenitic stainless steel components from the decommissioned advanced thermal prototype reactor "Fugen" has been characterized. Cast stainless steel materials were obtained from recirculation pump casing. The actual time at temperature for the materials was 138,000 h at 275$$^{circ}$$C. The Fugen material show modest decrease in Charpy-impact properties and a small increase in micro-Vickers hardness in ferrite phase because of thermal aging at relatively low service temperatures. The fracture toughness prediction method (H3T model) predicts slightly lower values for Charpy-impact energy obtained from the Fugen material. The results from microstructural analysis suggest that the prediction method have the potential to provide higher accuracy by considerations of the activation energy for embrittlement at low service temperatures.

Oral presentation

Study of thermal aging embrittlement on stainless steels used Fugen nuclear reactor

Nogiwa, Kimihiro; Onitsuka, Takashi; Takeuchi, Tomoaki; Abe, Teruyoshi; Sakakibara, Yasuhide; Horie, Kaoru; Nakamura, Takahisa

no journal, , 

no abstracts in English

Oral presentation

Dynamical interaction between a screw dislocation and a void in pure iron using molecular dynamics

Okubo, Manabu*; Onitsuka, Takashi*; Fukumoto, Kenichi*; Suzudo, Tomoaki

no journal, , 

In structural materials of fast breeder and fusion rectors, vacancies produced by radiation displacements are clustered and form voids. Experimental evidence indicates that the voids become obstacles of dislocation motion and cause hardening of the materials, but the detailed mechanism of the hardening has not been clear. In the current study, we perform molecular dynamics simulation of the interaction between a screw dislocation and a void to clarify the radiation hardening mechanism. Our results clearly show that the screw dislocation is pinned between the center of the void and its rear interface.

Oral presentation

Analyses of dynamic interactions between void and screw dislocation in BCC metals using molecular dynamics

Onitsuka, Takashi*; Okubo, Manabu*; Fukumoto, Kenichi*; Suzudo, Tomoaki

no journal, , 

Many of BCC metals are used as structural materials in nuclear devices. A possible cause of embrittlement of such metals under neutron radiation is accumulation of lattice defects that hamper the dislocation motions. Molecular dynamics have been used for the analyses of such dislocation motions, but interaction mechanism between the lattice defects and screw dislocation are still unclear. In this talk, we utilize molecular dynamics and analyze the interaction between void and screw dislocation in BCC Fe.

Oral presentation

Molecular dynamics studies on interaction between a screw dislocation and a void in pure Fe, 2

Onitsuka, Takashi*; Okubo, Manabu*; Suzudo, Tomoaki; Fukumoto, Kenichi*

no journal, , 

Reactor structural materials such as pressure vessels become brittle under neutron irradiation. It is widely known that a cause of such phenomenon could be formation of extended lattice defects under irradiation such as voids that become obstacles for dislocation motion, but we do not know the strength of these obstacles accurately enough for establishing a quantitative model. In the present study, we choose pure iron as a substitute of steel and numerically simulate the interaction between screw dislocation and a void using molecular dynamics method. Especially, we analyze the critical shear stress.

Oral presentation

Molecular dynamics studies on interaction between a screw dislocation and a void in pure Fe, 5

Taniguchi, Keisuke*; Onitsuka, Takashi*; Fukumoto, Kenichi*; Suzudo, Tomoaki

no journal, , 

It is known that a cause of irradiation hardening of nuclear materials by neutron irradiation can be ascribed to voids as an obstacle against dislocation motion. In this research, molecular dynamics (MD) simulations were exploited in order to analyze the dynamical reaction mechanism at the atomic level of the screw dislocation and void in BCC pure Fe. In particular, the relationship between the dislocation-void contact position and the strength of interaction was analyzed. As a result, it turned out that there is a rule between the contact position and the shear stress.

Oral presentation

Screw dislocation behavior in BCC Fe; Study using molecular dynamics simulations

Suzudo, Tomoaki; Onitsuka, Takashi*; Fukumoto, Kenichi*

no journal, , 

The irradiation produces various defects such as dislocation loops, voids, and solute clusters. Since they become obstacles for dislocations, research on the interaction between dislocations and obstacles has been pursued. Regarding the slip plane of BCC iron, the slip plane is {110} at low temperature but changes to {112} when the temperature increases to about room temperature; however, this phenomena has not been reproduced by molecular dynamics. We reconsidered the interatomic potential to reproduce the above temperature transition of the slip plane by molecular dynamics. In addition, the mechanism of the transition was discussed from the Peierls potential of the screw dislocation. As a result, it was found that the temperature transition of the slip plane can be reproduced by selecting an appropriate interatomic potential. It was also found that the temperature transition was likely to have been caused by temperature fluctuations of the lattice.

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