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Journal Articles

Migration energy of a self-interstitial atom in $$alpha$$-iron estimated by in situ observation of interstitial clusters at low temperatures using high-voltage electron microscopy

Abe, Yosuke; Sato, Yuki*; Hashimoto, Naoyuki*

Philosophical Magazine, 101(14), p.1619 - 1631, 2021/07

 Times Cited Count:1 Percentile:72.02(Materials Science, Multidisciplinary)

Modeling cluster dynamics or rate theory to describe the microstructural evolution of irradiated materials requires a precise knowledge of the migration energy of a self-interstitial atom (SIA), a product of energetic particle radiation. We measured the evolution of the number density of SIA clusters in electron-irradiated $$alpha$$-iron at low temperatures (110-320 K) by in situ observation using high-voltage electron microscopy. We identified temperature-dependent physical quantities, including (1) the peak density of SIA clusters and (2) the critical defect-free zone thickness in a thin foil specimen, associated with interstitial mobility. By fitting these quantities to the Arrhenius relations derived by rate theory analysis, we obtained estimated interstitial migration energy values of $$0.26 pm 0.04$$ and $$0.30 pm 0.03$$ eV for (1) and (2), respectively.

Journal Articles

Change in damping capacity arising from twin-boundary segregation in solid-solution magnesium alloys

Somekawa, Hidetoshi*; Basha, D. A.*; Singh, A.*; Tsuru, Tomohito; Watanabe, Hiroyuki*

Philosophical Magazine Letters, 100(10), p.494 - 505, 2020/10

 Times Cited Count:2 Percentile:45.37(Materials Science, Multidisciplinary)

The damping capacity in the vicinity of {10$$bar{1}$$2} twin boundaries was measured before and after annealing by nano-dynamic mechanical analysis. The subsequent annealing process led to a lower damping capacity in all magnesium binary alloys, which was in contrast to the results in pure magnesium. This is on account of the segregation of solute atoms in incoherent twin boundaries. The alloying elements, which have the characteristic of a low segregation energy for twin boundaries, effectively prevents the damping capacity degradation.

Journal Articles

Quasi-one-dimensional magnetic interactions and conduction electrons in EuCu$$_5$$ and EuAu$$_5$$ with the characteristic hexagonal structure

Matsuda, Shinya*; Ota, Joji*; Nakaima, Kenri*; Iha, Wataru*; Gochi, Jun*; Uwatoko, Yoshiya*; Nakashima, Miho*; Amako, Yasushi*; Honda, Fuminori*; Aoki, Dai*; et al.

Philosophical Magazine, 100(10), p.1244 - 1257, 2020/04

 Times Cited Count:2 Percentile:45.37(Materials Science, Multidisciplinary)

Journal Articles

Effects of one-dimensional migration of self-interstitial atom clusters on the decreasing behaviour of their number density in electron-irradiated $$alpha$$-iron

Abe, Yosuke; Sato, Yuki*; Hashimoto, Naoyuki*; Onuki, Somei*

Philosophical Magazine, 100(1), p.110 - 125, 2020/00

 Times Cited Count:2 Percentile:25.87(Materials Science, Multidisciplinary)

We derive analytical models associated with the experimentally revealed one-dimensional (1D) migration mechanisms to examine the decreasing behavior of the cluster number density. The model calculation indicates that the detrapping of the stationary SIA clusters causes the surface annihilation of the liberated SIA clusters, leading to the decrease in their number density. The decreasing behavior is in closer accordance with the experimental data when setting the impurity concentration in the same order as the estimation from the previous in situ HVEM experiment. This result suggests that the trapping and detrapping of the SIA clusters are the possible underlying processes for the decreasing behavior.

Journal Articles

Characterisation of structural similarities of precipitates in Mg-Zn and Al-Zn-Mg alloys systems

Bendo, A.*; Maeda, Tomoyoshi*; Matsuda, Kenji*; Lervik, A.*; Holmestad, R.*; Marioara, C. D.*; Nishimura, Katsuhiko*; Nunomura, Norio*; Toda, Hiroyuki*; Yamaguchi, Masatake; et al.

Philosophical Magazine, 99(21), p.2619 - 2635, 2019/07

 Times Cited Count:13 Percentile:83.11(Materials Science, Multidisciplinary)

Journal Articles

Effects of stacking fault energies on formation of irradiation-induced defects at various temperatures in face-centred cubic metals

Nakanishi, Daiki*; Kawabata, Tomoya*; Doihara, Kohei*; Okita, Taira*; Itakura, Mitsuhiro; Suzuki, Katsuyuki*

Philosophical Magazine, 98(33), p.3034 - 3047, 2018/09

 Times Cited Count:4 Percentile:36.14(Materials Science, Multidisciplinary)

By using the six sets of interatomic potentials for face-centredcubic metals that differ in the stacking fault energy (SFE) while most of the other material parameters are kept almost identical, we conducted molecular dynamics simulations to evaluate the effects of SFE on the defect formation process through collision cascades. The ratio of glissile SIA clusters tends to decrease with increasing SFE. This is because perfect loops, the edges of which split into two partial dislocations with stacking fault structures between them in most cases, prefer to form at lower SFEs. The enhanced formation of glissile SIA clusters at lower SFEs can also be observed even at increased temperature.

Journal Articles

Interactions between clusters of self-interstitial atoms via a conservative climb in BCC-Fe

Hayakawa, Sho*; Okita, Taira*; Itakura, Mitsuhiro; Aichi, Masaatsu*; Suzuki, Katsuyuki*

Philosophical Magazine, 98(25), p.2311 - 2325, 2018/06

 Times Cited Count:3 Percentile:28.45(Materials Science, Multidisciplinary)

We conduct kinetic Monte Carlo simulations for the conservative climb motion of a cluster of self-interstitial atoms towards another SIA cluster in BCC Fe; the conservative climb velocity is inversely proportional to the fourth power of the distance between them, as per the prediction based on Einstein's equation. The size of the climbing cluster significantly affects its conservative climb velocity, while the size of the cluster that originates the stress field does not. The activation energy for the conservative climb is considerably greater than that derived in previous studies and strongly dependent on the climbing cluster size.

Journal Articles

Atomic simulations to evaluate effects of stacking fault energy on interactions between edge dislocation and spherical void in face-centred cubic metals

Doihara, Kohei*; Okita, Taira*; Itakura, Mitsuhiro; Aichi, Masaatsu*; Suzuki, Katsuyuki*

Philosophical Magazine, 98(22), p.2061 - 2076, 2018/05

 Times Cited Count:9 Percentile:63.65(Materials Science, Multidisciplinary)

In this study, molecular dynamics simulations were performed to elucidate the effects of stacking fault energy (SFE) on the physical interactions between an edge dislocation and a spherical void in the crystal structure of face-centred cubic metals at various temperatures and for different void sizes. Four different types of interaction morphologies were observed, in which (1) two partial dislocations detached from the void separately, and the maximum stress corresponded to the detachment of the trailing partial; (2) two partial dislocations detached from the void separately, and the maximum stress corresponded to the detachment of the leading partial; (3) the partial dislocations detached from the void almost simultaneously without jog formation; and (4) the partial dislocations detached from the void almost simultaneously with jog formation. With an increase in void size or SFE, the interaction morphology changed in the above-mentioned order. It was observed that the magnitude of the critical resolved shear stress (CRSS) and its dependence on the SFE were determined by these interaction morphologies. The value of the CRSS in the case of interaction morphology (1) is almost equal to an analytical one based on the linear elasticity by employing the Burgers vector of a single partial dislocation. The maximum value of the CRSS is also obtained by the analytical model with the Burgers vector of the two partial dislocations.

Journal Articles

Consideration of the oxide particle-dislocation interaction in 9Cr-ODS steel

Ijiri, Yuta*; Ono, Naoko*; Ukai, Shigeharu*; Yu, H.*; Otsuka, Satoshi; Abe, Yosuke; Matsukawa, Yoshitaka*

Philosophical Magazine, 97(13), p.1047 - 1056, 2017/02

 Times Cited Count:2 Percentile:17.39(Materials Science, Multidisciplinary)

The interaction between oxide particles and dislocations in a 9Cr-ODS ferritic steel is investigated by both static and in-situ TEM observation under dynamic straining conditions and room temperature. The measured obstacle strength ($$alpha$$) of the oxide particles was no greater than 0.80 and the average was 0.63. The dislocation loops around some coarsened particles were also observed. The calculated obstacle strength by a stress formula of the Orowan interaction is nearly equaled to the average experimental value. Not only cross-slip system but also the Orowan interaction should be considered as the main interaction mechanism between oxide particles and dislocation in 9Cr-ODS ferritic steel.

Journal Articles

Vacancy effects on one-dimensional migration of interstitial clusters in iron under electron irradiation at low temperatures

Sato, Yuki*; Abe, Yosuke; Abe, Hiroaki*; Matsukawa, Yoshitaka*; Kano, Sho*; Onuki, Somei*; Hashimoto, Naoyuki*

Philosophical Magazine, 96(21), p.2219 - 2242, 2016/06

 Times Cited Count:7 Percentile:45.78(Materials Science, Multidisciplinary)

We performed in situ observation of one-dimensional (1D) migration of self-interstitial atom (SIA) clusters in iron under electron irradiation at 110-300 K using high-voltage electron microscopy. Most 1D migration was stepwise positional changes of SIA clusters at irregular time intervals at all temperatures. The frequency of 1D migration did not depend on the irradiation temperature. It was directly proportional to the damage rate, suggesting that 1D migration was induced by electron irradiation. In contrast, the 1D migration distance depended on the temperature: distribution of the distance ranged over 100 nm above 250 K, decreased steeply between 250 and 150 K and was less than 20 nm below 150 K. The distance was independent of the damage rate at all temperatures. Next, we examined fluctuation in the interaction energy between an SIA cluster and vacancies of random distribution at concentrations $$10^{-4}$$-$$10^{-2}$$, using molecular statics simulations. The fluctuation was found to trap SIA clusters of 4 nm diameter at vacancy concentrations higher than $$10^{-3}$$. We proposed that 1D migration was interrupted by impurity atoms at temperatures higher than 250 K, and by vacancies accumulated at high concentration under electron irradiation at low temperatures where vacancies are not thermally mobile.

Journal Articles

Presence of $$varepsilon$$-martensite as an intermediate phase during the strain-induced transformation of SUS304 stainless steel

Hatano, Masaharu*; Kubota, Yoshiki*; Shobu, Takahisa; Mori, Shigeo*

Philosophical Magazine Letters, 96(6), p.220 - 227, 2016/06

 Times Cited Count:6 Percentile:40.83(Materials Science, Multidisciplinary)

We have investigated the formation process of $$alpha$$'-martensite from the $$gamma$$-phase induced by external strain using ${it in situ}$ synchrotron diffraction experiments, combined with Lorentz transmission electron microscopy (TEM) and high-resolution TEM observations. It is clearly demonstrated that $$varepsilon$$-martensite with hexagonal symmetry appears as an intermediate structure during the plastic deformation of SUS304 stainless steel. In addition to stacking faults and dislocations, interfaces between the twin structures presumably play a key role in the formation of $$varepsilon$$-martensite.

Journal Articles

Material design for magnesium alloys with high deformability

Somekawa, Hidetoshi*; Yamaguchi, Masatake; Osawa, Yoshiaki*; Singh, A.*; Itakura, Mitsuhiro; Tsuru, Tomohito; Mukai, Toshiji*

Philosophical Magazine, 95(8), p.869 - 885, 2015/02

 Times Cited Count:18 Percentile:73.71(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Single crystal growth and characterization of URu$$_2$$Si$$_2$$

Haga, Yoshinori; Matsuda, Tatsuma*; Tateiwa, Naoyuki; Yamamoto, Etsuji; Onuki, Yoshichika; Fisk, Z.

Philosophical Magazine, 94(32-33), p.3672 - 3680, 2014/11

 Times Cited Count:5 Percentile:32.87(Materials Science, Multidisciplinary)

Journal Articles

Multiscale thermodynamic analysis on fracture toughness loss induced by solute segregation in steel

Yamaguchi, Masatake; Kameda, Jun*

Philosophical Magazine, 94(19), p.2131 - 2149, 2014/04

 Times Cited Count:11 Percentile:56.01(Materials Science, Multidisciplinary)

A significant loss of fracture toughness ($$K_{rm Ic}$$) is induced by intergranular (grain boundary; GB) segregation of metalloid solute in alloy steels. Yet, the mechanism has not been clarified from a multiscale point of view. From a thermodynamic approach aided by first-principles calculations, we show here that segregated solute with higher energetic stability on fracture surfaces causes a larger linear reduction in the ideal work to intergranular fracture ($$2gamma_{rm int}$$); i.e., the energy difference between a GB and its two fracture surfaces. Remarkably, the combined analysis with first-principles calculations and fracture mechanics experiments found several orders of magnitude more energy loss in $$K_{rm Ic}$$ for a specific range in the $$2gamma_{rm int}$$ within only a few tenths of J/m$$^2$$. These results illustrate that the GB of steel has the threshold energy of atomic cohesion under which catastrophic failure occurs.

Journal Articles

X-ray backscattering study of crystal lattice distortion in hidden order of URu$$_2$$Si$$_2$$

Tabata, Chihiro*; Inami, Toshiya; Michimura, Shinji*; Yokoyama, Makoto*; Hidaka, Hiroyuki*; Yanagisawa, Tatsuya*; Amitsuka, Hiroshi*

Philosophical Magazine, 94(32-33), p.3691 - 3701, 2014/00

 Times Cited Count:14 Percentile:64.03(Materials Science, Multidisciplinary)

Journal Articles

Mobile effect of hydrogen on intergranular decohesion of iron; First-principles calculations

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

Philosophical Magazine, 92(11), p.1349 - 1368, 2012/04

 Times Cited Count:37 Percentile:88.41(Materials Science, Multidisciplinary)

Atomistic mechanisms of hydrogen-induced cracking along a bcc Fe $$Sigma 3(111)$$ symmetrical tilt grain boundary (GB) have been studied by first-principles calculations. The mobile and immobile effects of hydrogen on the GB decohesion are analyzed by calculating the dependence of hydrogen segregation energy on the coverage relevant to the repulsive interaction among segregated hydrogen atoms at the GB and on its fracture surfaces, together with generalizing McLean's formula. It was found that the segregation of combined mobile and immobile hydrogen atoms from the bulk and/or GB on the fracture surfaces causes much stronger reduction (70-80%) in the GB cohesive energy. It can occur even at a very low bulk hydrogen content of about 10$$^{-9}$$ atomic fraction during slow cracking. This is in contrast with only 10-20% decohesion induced by immobile hydrogen at much higher hydrogen content during fast cracking.

Journal Articles

Effect of Sn and Nb on generalized stacking fault energy surfaces in zirconium and $$gamma$$ hydride habit planes

Udagawa, Yutaka; Yamaguchi, Masatake; Tsuru, Tomohito; Abe, Hiroaki*; Sekimura, Naoto*

Philosophical Magazine, 91(12), p.1665 - 1678, 2011/04

 Times Cited Count:13 Percentile:61.58(Materials Science, Multidisciplinary)

We have investigated the effects of Sn and Nb on dislocation properties in a Zr lattice in order to elucidate the role of these alloying elements in hydride nucleation processes. According to experimental observations, $$gamma$$-hydride habit planes are close to the prismatic plane in pure Zr and close to the basal plane in zircaloy. Dislocation loops are observed around hydride precipitates, implying they play a part in hydride formation. Our ab initio generalized-stacking-fault energy calculations showed remarkable effects of Sn on unstable-stacking energy and stacking-fault energy: these parameters for basal slip were considerably reduced while those for prismatic slip were increased in the presence of Sn. These results suggest selective stabilization and enhancement of dislocation spreading in the basal plane, promoting possible elementary processes of hydride precipitation with basal habit plane, i.e. screw-dislocation spreading and edge-dislocation emission in the basal plane.

Journal Articles

Deformation twinning of Bi-Sb solid alloy formed under a strong gravitational field

Iguchi, Yusuke*; Mashimo, Tsutomu*; Ono, Masao; Okayasu, Satoru

Philosophical Magazine Letters, 90(7), p.513 - 518, 2010/07

 Times Cited Count:4 Percentile:32.25(Materials Science, Multidisciplinary)

We performed an ultracentrifuge experiment on Bi-Sb alloy. Deformation twins with misorientations of about 90 $$^{circ}$$ were observed in the low-gravitational region where grain refinement had not occurred. The twins were thicker than the conventional deformation twins and their thickness was proportional to the gravitational field. We found that the minimum gravitational field required for grain refinement was 1.7$$times$$10 $$^{5}$$ G at 240 $$^{circ}$$C for periods $$<$$ 10 h.

Journal Articles

Stress and temperature dependence of the structure of the martensite and X-phase in Ni$$_{2}$$MnGa

Fukuda, Takashi*; Terai, Tomoyuki*; Kushida, Hiroaki*; Kakeshita, Tomoyuki*; Osakabe, Toyotaka; Kakurai, Kazuhisa

Philosophical Magazine, 90(14), p.1925 - 1935, 2010/05

 Times Cited Count:6 Percentile:40.78(Materials Science, Multidisciplinary)

The stress and temperature dependence of the structure of the X-phase in Ni$$_{2}$$MnGa has been investigated by neutron diffraction measurements under compressive stress to clarify the structural relationship among the P-, I-, M- and X-phases. The structure of the X-phase in Ni$$_{2}$$MnGa depends strongly on stress and temperature compared to the M- or I-phase. In association with the X $$rightarrow$$ M transformation, both the position and intensity of the satellite reflection changes drastically, regardless of stress and temperature, while with X $$rightarrow$$ P transformation, the intensity of the satellite reflection fades gradually. For the I $$rightarrow$$ X transformation, the position and intensity of the satellite changes drastically when transformation occur under compressive stress, while the changes are continuous under zero stress. These results strongly suggest the existence of a multicritical point in Ni$$_{2}$$MnGa.

Journal Articles

Phase transformation of Cu precipitate in Fe-Cu alloy studied using self-guided molecular dynamics

Abe, Yosuke; Jitsukawa, Shiro

Philosophical Magazine Letters, 89(9), p.535 - 543, 2009/09

 Times Cited Count:5 Percentile:39.05(Materials Science, Multidisciplinary)

The self-guided molecular dynamics (SGMD) method which can enhance the conformational sampling efficiency in MD simulations, was applied in investigating the phase transformation of Cu precipitate in $$alpha$$-iron that took place during thermal ageing. It was shown that the SGMD method can accelerate calculating the bcc to 9R structure transformation of a small precipitate (even 4.0 nm in size), enabling the transformation without introducing any excess vacancies. The size dependence of the transformation also agreed with that seen in previous experimental studies.

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