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Journal Articles

Brittle-fracture simulations of curved cleavage cracks in $$alpha$$-iron; A Molecular dynamics study

Suzudo, Tomoaki; Ebihara, Kenichi; Tsuru, Tomohito

AIP Advances (Internet), 10(11), p.115209_1 - 115209_8, 2020/11

 Times Cited Count:0 Percentile:100(Nanoscience & Nanotechnology)

The mechanism of their brittle fracture of BCC metals is not fully understood. In this study, we conduct a series of three-dimensional molecular dynamics simulations of cleavage fracture of $$alpha$$-iron. In particular, we focus on mode-I loading starting from curved crack fronts. In the simulations, brittle fractures are observed at cleavages on the {100} plane, while the initial cracks become blunted on other planes as a result of dislocation emissions. Our modeling results agreed with a common experimental observation, that is, {100} is the preferential cleavage plane in bcc transition metals.

Journal Articles

Atomistic modeling of hardening in spinodally-decomposed Fe-Cr binary alloys

Suzudo, Tomoaki; Takamizawa, Hisashi; Nishiyama, Yutaka; Caro, A.*; Toyama, Takeshi*; Nagai, Yasuyoshi*

Journal of Nuclear Materials, 540, p.152306_1 - 152306_10, 2020/11

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Spinodal decomposition in thermally aged Fe-Cr alloys leads to significant hardening, which is the direct cause of the so-called 475C-embrittlement. To illustrate how spinodal decomposition induces hardening by atomistic interactions, we conducted a series of numerical simulations as well as reference experiments. The numerical results indicated that the hardness scales linearly with the short-range order (SRO) parameter, while the experimental result reproduced this relationship within statistical error. Both seemingly suggest that neighboring Cr-Cr atomic pairs essentially cause hardening, because SRO is by definition uniquely dependent on the appearance probability of such pairs. A further numerical investigation supported this notion, as it suggests that the dominant cause of hardening is the pinning effect of dislocations passing over such Cr-Cr pairs.

Journal Articles

Molecular dynamics study of phosphorus migration in $$Sigma$$5 grain boundary of $$alpha$$-iron

Ebihara, Kenichi; Suzudo, Tomoaki

Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.65 - 69, 2020/10

Phosphorus (P) is known as one of the elements which cause the grain boundary (GB) embrittlement in steels and its GB segregation is promoted by the increase of vacancies and self-interstitial atoms due to irradiation. Thus we have been developing the rate-theory model for estimating GB P segregation under several temperatures and irradiation conditions. Because the model does not include the trapping and de-trapping processes properly, however, the model cannot calculate GB P coverage which is measured by experiments. As for the de-trapping process, so far, we have considered the migration of a P atom in the GB region of $$Sigma$$3 symmetrical tilt GB using molecular dynamics (MD). In the current study, we also simulated the P migration in $$Sigma$$5 GB using MD and compared the result with that of $$Sigma$$3. As a result, at 800K, it was found that a P atom cannot migrate in $$Sigma$$5 without vacancies while a P atom can migrate between iron atoms in $$Sigma$$3.

Journal Articles

${it In situ}$ WB-STEM observation of dislocation loop behavior in reactor pressure vessel steel during post-irradiation annealing

Du, Y.*; Yoshida, Kenta*; Shimada, Yusuke*; Toyama, Takeshi*; Inoue, Koji*; Arakawa, Kazuto*; Suzudo, Tomoaki; Milan, K. J.*; Gerard, R.*; Onuki, Somei*; et al.

Materialia, 12, p.100778_1 - 100778_10, 2020/08

In order to ensure the integrity of the reactor pressure vessel in the long term, it is necessary to understand the effects of irradiation on the materials. In this study, irradiation-induced dislocation loops were observed in neutron-irradiated reactor pressure vessel specimens during annealing using our newly developed WB-STEM. It was confirmed that the proportion of $$<100>$$ loops increased with increasing annealing temperature. We also succeeded in observing the phenomenon that two $$frac{1}{2}$$$$<111>$$ loops collide into a $$<100>$$ loop. Moreover, a phenomenon in which dislocation loops decorate dislocations was also observed, and the mechanism was successfully explained by molecular dynamics simulation.

Journal Articles

Molecular dynamics simulations of phosphorus migration in a grain boundary of $$alpha$$-iron

Ebihara, Kenichi; Suzudo, Tomoaki

TMS 2020; 149th Annual Meeting & Exhibition Supplemental Proceedings, p.995 - 1002, 2020/02

Phosphorus (P) is known as an element which causes grain boundary (GB) embrittlement in steels. In addition, GB P segregation is promoted by the increase of vacancies and self interstitial atoms due to irradiation. Thus, the diffusion rate theory model for estimating irradiation-induced GB P segregation has been developed based on the atomic processes. Since the present model does not include the trapping and de-trapping processes at GBs, however, it cannot calculate the value which is directly compared with experimental results. In this study, we simulated the migration of a P atom in the $$Sigma$$3(111) symmetrical tilt GB. In addition, by tracking the migration of the P atom, the diffusion barrier energy was evaluated. As a result, the diffusion barrier energy was almost the same as the P segregation energy of an interstitial site in the GB, and it was found that P atoms migrate via interstitial sites in the GB.

Journal Articles

Atomistic simulation of phosphorus segregation to $$Sigma$$3(111) symmetrical tilt grain boundary in $$alpha$$-iron

Ebihara, Kenichi; Suzudo, Tomoaki

Modelling and Simulation in Materials Science and Engineering, 26(6), p.065005_1 - 065005_10, 2018/09

 Times Cited Count:1 Percentile:89.52(Materials Science, Multidisciplinary)

Irradiation-induced grain boundary phosphorus segregation is an important factor for estimating the embrittlement of nuclear reactor pressure vessel steels, but the physical process of phosphorus migration to grain boundaries is still unclear. We numerically studied phosphorus migration toward $$Sigma$$3(111) symmetrical tilt grain boundary in $$alpha$$-iron using molecular dynamics. We found that, in the vicinity of the grain boundary within $$sim$$1 nm distance, an iron-phosphorus mixed dumbbell and an octahedral interstitial phosphorus atom push a self-interstitial atom into the grain boundary, and the phosphorus atom becomes a substitutional atom. A phosphorus vacancy complex in the region also becomes dissociated, and the vacancy is absorbed in the grain boundary without dragging phosphorus. The results claim that a novel view of the segregation process is required.

Journal Articles

Molecular dynamics simulations of cesium adsorption on illite nanoparticles

Lammers, L.*; Bourg, I. C.*; Okumura, Masahiko; Kolluri, K.*; Sposito, G.*; Machida, Masahiko

Journal of Colloid and Interface Science, 490, p.608 - 620, 2017/03

 Times Cited Count:46 Percentile:9.33(Chemistry, Physical)

no abstracts in English

Journal Articles

Molecular dynamics simulation of telomeric single-stranded DNA and POT1

Kaburagi, Masaaki; Yamada, Hironao*; Miyakawa, Takeshi*; Morikawa, Ryota*; Takasu, Masako*; Kato, Takamitsu*; Uesaka, Mitsuru*

Polymer Journal, 48(2), p.189 - 195, 2016/02

 Times Cited Count:4 Percentile:76.26(Polymer Science)

We performed molecular dynamics (MD) simulations of telomeric single-stranded DNA and POT1 for 100 ns. The distance between $$C_alpha$$ (POT1) and O5' (telomeric ssDNA) is calculated to verify the binding system for 100 ns MD. We then calculated the distance between the bases of telomeric DNA ends and the root mean square deviation and gyration radius in single and binding states. We compared the root mean square fluctuations between single and binding states and calculated the number of hydrogen bonds between POT1 and telomeric DNA. There are many hydrogen bonds between Gln94 and the first guanine of the closest TTAGGG sequence in telomeric single-stranded DNA. These Gln94 and the guanine have a large difference in root mean square fluctuation between single and binding states. We found that Gln94 and guanine are important components of the binding system, and they are related to its stability.

Journal Articles

Protein boson peak originated from hydration-related multiple minima energy landscape

Jochi, Yasumasa*; Kitao, Akio*; Go, Nobuhiro

Journal of the American Chemical Society, 127(24), p.8705 - 8709, 2005/06

 Times Cited Count:27 Percentile:36.79(Chemistry, Multidisciplinary)

no abstracts in English

Journal Articles

Parallel molecular-dynamics simulation on ITBL

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

Journal Articles

An Introduction of parallel molecular dynamics stencil, 3

Shimizu, Futoshi; Kaburaki, Hideo

Ansanburu, (22), p.23 - 29, 2003/04

no abstracts in English

Journal Articles

Short-range structure of vitreous P$$_{2}$$O$$_{5}$$ by MD simulation

Suzuki, Yoshihiro*; Takase, Keiichi*; Akiyama, Isao*; Suzuya, Kentaro; Umesaki, Norimasa*; Otori, Norikazu*

Materials Transactions, 42(11), p.2242 - 2246, 2001/11

 Times Cited Count:7 Percentile:51.03(Materials Science, Multidisciplinary)

We have performed the molecular dynamics (MD) simulations for vitreous P$$_{2}$$O$$_{5}$$ using isotropic pair potentials composed only of coulombic and repulsive interaction. The obtained P-O pair distribution function reproduced the two peaks expected from the results of neutron diffraction experiments, in the nearest-neighbor P-O correlation. The neutron-weighted real-space correlation function were also in semi-quantitative agreement with that from the experimental results. The distribution of coordination number for O around P and P around O showed that most P atoms form tetrahedral PO$$_{4}$$ units in the glass and three-fifths of O atoms are bridging oxygen, O$$_{B}$$, and the others are terminal one, O$$_{T}$$. The pair distribution functions for P-O$$_{B}$$ and P-O$$_{T}$$ clarified the PO$$_{4}$$ units have three long P-O$$_{B}$$ bonds and one short P-O$$_{T}$$ bond. We have concluded that the short-range structure for vitreous P$$_{2}$$O$$_{5}$$ agrees well with the picture derived from many experiments.

Oral presentation

Diffusion of uranyl ions in water and montmorillonite; Molecular dynamics calculation

Arima, Tatsumi*; Inagaki, Yaohiro*; Idemitsu, Kazuya*; Kawamura, Katsuyuki*; Yotsuji, Kenji; Tachi, Yukio

no journal, , 

Molecular dynamics simulations of uranyl ion - carbonate ion - clay - water systems were performed to investigate diffusion behavior of uranyl ion in free water and montmorillonite interlayer.

Oral presentation

Interaction between facet voids and dislocations in BCC Fe

Yabuuchi, Kiyohiro*; Kimura, Akihiko*; Suzudo, Tomoaki

no journal, , 

Irradiation of high-energy particles into materials induces the formation of various lattice defects, which significantly influence their mechanical properties. Voids, which are aggregates of vacancies, are among such defects and become obstacles causing materials hardening. So far, we have been investigating obstacle strength factor of the facet voids created by ion-beam irradiation to pure Fe crystals. Because some ambiguity of the experimentally-measured factor was observed, we suspect that positional relation between interacting voids and dislocations influence the factor. The current study aimed at numerically investigating how this positional relation influences the factor by using molecular dynamics.

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

Atomistic study on the generation and gliding properties of pyramidal dislocations in magnesium

Kaburaki, Hideo; Itakura, Mitsuhiro; Yamaguchi, Masatake

no journal, , 

Oral presentation

Study on the process of grain boundary phosphorus segregation by molecular dynamics simulation

Ebihara, Kenichi; Suzudo, Tomoaki; Yamaguchi, Masatake

no journal, , 

no abstracts in English

30 (Records 1-20 displayed on this page)