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Journal Articles

The Two-step nucleation of G-phase in ferrite

Matsukawa, Yoshitaka*; Takeuchi, Tomoaki; Kakubo, Yuta*; Suzudo, Tomoaki; Watanabe, Hideo*; Abe, Hiroaki*; Toyama, Takeshi*; Nagai, Yasuyoshi*

Acta Materialia, 116, p.104 - 113, 2016/09

https://doi.org/10.1016/j.actamat.2016.06.013

Times Cited Count：73 Percentile：95.76(Materials Science, Multidisciplinary)

Atom probe tomography (APT) and TEM were combined for identifying the stage at which solute clusters transform into compounds crystallographically distinct from the matrix, in the precipitation of the G-phase (Ni $_{16}$ Si $_{7}$ Mn $_{6}$ ) from ferrite solid solution subjected to isothermal annealing at 673 K. Based on a systematic analysis of solute clusters as a function of annealing time, the nucleation of the G-phase was found to occur via a two-step process. Moreover, the structural change was found to occur via another two-step process. There was a time lag between the end of cluster growth to become a critical size and the start of the structural change. During the incubation period solute enrichment occurred inside the clusters without further size growth, indicating that the nucleation of the G-phase occurs at the critical size with a critical composition. Judging from the results of APT, TEM and the simulation of electron diffraction patterns, the critical composition was estimated to be Ni $_{16}$ Si $_{3.5}$ (Fe,Cr) $_{3.5}$ Mn $_{6}$ .

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

https://doi.org/10.1080/14786435.2016.1194533

Times Cited Count：12 Percentile：51.44(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

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

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

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

https://doi.org/10.1080/14786435.2010.543651

Times Cited Count：18 Percentile：65.36(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, -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

Ab initio study on plane defects in zirconium-hydrogen solid solution and zirconium hydride

Udagawa, Yutaka; Yamaguchi, Masatake; Abe, Hiroaki*; Sekimura, Naoto*; Fuketa, Toyoshi

Acta Materialia, 58(11), p.3927 - 3938, 2010/06

https://doi.org/10.1016/j.actamat.2010.03.034

Times Cited Count：101 Percentile：96.45(Materials Science, Multidisciplinary)

Journal Articles

TEM observation of growth process of zirconium hydride in zircaloy-4 during hydrogen ion implantation

Shinohara, Yasunari*; Abe, Hiroaki*; Iwai, Takeo*; Sekimura, Naoto*; Kido, Toshiya*; Yamamoto, Hiroyuki; Taguchi, Tomitsugu

Journal of Nuclear Science and Technology, 46(6), p.564 - 571, 2009/06

https://doi.org/10.3327/jnst.46.564

Times Cited Count：30 Percentile：87.31(Nuclear Science & Technology)

observation during hydrogen ion implantation was performed with a TEM installed in an ion accelerator to investigate the growth process of Zr hydride in Zicaloy-4. To clarify the effect of radiation damage, some samples were irradiated with 4 MeV Ni $^{3+}$ ions prior to hydrogen implantation. Growth processes of Zr hydrides accompanying the formation of dislocations were observed. The crystallographic relationship between the Zr matrix and Zr hydrides was identical with that found in previous studies: inter- and intragranular hydrides exhibiting a tendency to grow in the 110 direction. This growth can be attributed to a shear mechanism. In specimens preirradiated with Ni ions, the growth rate of hydrides was suppressed, but the growth direction was not affected by radiation defects. It was also confirmed that the black spots induced by Ni $^{3+}$ ion irradiation grew during hydrogen ion implantation, suggesting the formation of hydrides at the defects.

Journal Articles

Polymeric chains in C $_{60}$ and Co mixture

Lavrentiev, V.*; Abe, Hiroaki*; Naramoto, Hiroshi*; Sakai, Seiji; Narumi, Kazumasa

Chemical Physics Letters, 424(1-3), p.101 - 104, 2006/06

https://doi.org/10.1016/j.cplett.2006.04.046

Times Cited Count：14 Percentile：43.41(Chemistry, Physical)

We present transmission electron beam identification of C $_{60}$ -based polymeric chains in the mixture between Co and C $_{60}$ simultaneously deposited on (001) NaCl at room temperature. Estimation of intrachain distances taken from the direct image suggests bridging position of Co atoms between buckyballs. The chains tend to be coupled due to Coulomb interaction between the charged units of the polymers. We have confirmed the charge transfer between Co and C $_{60}$ detecting 0.6 eV upward shift of C $_{60}$ LUMO-derived peak in the electron-energy-loss spectrum of mixture. The systematic shifts of energy-loss $^{*}$ peaks imply distortion of C $_{60}$ cages belonging to the polymeric chains.

Journal Articles

Chemically driven microstructure evolution in cobalt-fullerene mixed system

Lavrentiev, V.; Naramoto, Hiroshi; Abe, Hiroaki*; Yamamoto, Shunya; Narumi, Kazumasa; Sakai, Seiji

Fullerenes, Nanotubes, and Carbon Nanostructures, 12(1-2), p.519 - 528, 2004/00

https://doi.org/10.1081/FST-120027216

Times Cited Count：3 Percentile：16.41(Chemistry, Physical)

no abstracts in English

Journal Articles

Influence of H and He on corrosion behavior of ion irradiated stainless steel

Nemoto, Yoshiyuki; Miwa, Yukio; Tsuji, Hirokazu; Tsukada, Takashi; Abe, Hiroaki*; Sekimura, Naoto*

JAERI-Review 2003-033, TIARA Annual Report 2002, p.171 - 173, 2003/11

https://jopss.jaea.go.jp/pdfdata/JAERI-Review-2003-033-p0001-p0187.pdf

The aim of this work is to evaluate corrosion behavior of irradiated materials for mechanistic understanding of irradiation assisted stress corrosion cracking (IASCC). Solution annealed high purity Fe-18Cr-12Ni specimens were used in this study. H and He were implanted during irradiation with 12MeV Ni $^{3+}$ ion at 573K. After corrosion procedure, the specimens were examined with atomic force microscope (AFM) to evaluate corrosion behavior. It was shown that the corroded volume of irradiated area increased with radiation damage. H implantation at lower temperature accelerated corrosion. He implantation suppressed corrosion.

Journal Articles

Nanoparticle formation by pulsed laser ablation of TiO $_{2}$

Yamaki, Tetsuya; Ito, Hisayoshi; Matsubara, Masakazu*; Abe, Hiroaki*; Asai, Keisuke*

Transactions of the Materials Research Society of Japan, 28(3), p.879 - 882, 2003/10

Titanium oxide nanoparticles were formed by pulsed laser ablation of a TiO $_{2}$ rutile pellet with a KrF excimer laser ( = 248 nm). The ablation was performed in atmospheres of Ar and O $_{2}$ at total pressures ranging from 0.2 and 10 Torr. At a higher pressure than 1 Torr, Ti in the nanoparticles had an oxidation state of 4+ to form TiO $_{2}$ . According to the X-ray diffraction analyses, the nanopartiles were found to contain both the anatase and rutile phases, which crystallized through extremely energetic, non-equilibrium reactions in an ablation plume. In contrast, at pressures of 0.2 and 0.5 Torr, the nanoparticles were composed of dominant TiO $_{2}$ with a small amount of a less oxidized phase such as Ti $_{2}$ O $_{3}$ . The important result is that the XRD patterns of the samples prepared at 1 and 5 Torr showed the different anatase-to-rutile ratio of the peak intensities. This indicates that the weight fraction of the rutile/anatase crystalline phases can be controlled by the ambient gas pressure.

Journal Articles

Isolation of Co nanoparticles by C $_{60}$ molecules in co-deposited film

Lavrentiev, V.; Abe, Hiroaki*; Yamamoto, Shunya; Naramoto, Hiroshi; Narumi, Kazumasa

Materials Letters, 57(24-25), p.4093 - 4097, 2003/08

https://doi.org/10.1016/S0167-577X(03)00272-6

Times Cited Count：9 Percentile：38(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Preparation of TiO $_{2}$ nanoparticles by pulsed laser ablation; Ambient pressure dependence of crystallization

Matsubara, Masakazu*; Yamaki, Tetsuya; Ito, Hisayoshi; Abe, Hiroaki*; Asai, Keisuke*

Japanese Journal of Applied Physics, Part 2, 42(5A), p.L479 - L481, 2003/05

Pulsed laser ablation with a KrF excimer laser was used to prepare fine particles of titanium dioxide (TiO $_{2}$ ). The ablation in an atmosphere of Ar and O $_{2}$ (5:5) at total pressures of 1 Torr led to the formation of TiO $_{2}$ nanoparticles composed of anatase and rutile structures without any suboxides. The weight fraction of the rutile/anatase crystalline phases was controlled by the pressure of the Ar/O $_{2}$ gas. The TiO $_{2}$ nanoparticles had a spherical shape and their size, ranging from 10 and 14 nm, also appeared to be dependent on the ambient pressure.

Journal Articles

RBS and SEM analysis of the nickel-fullerene hybrid systems

Vacik, J.; Naramoto, Hiroshi; Narumi, Kazumasa; Yamamoto, Shunya; Abe, Hiroaki*

Nuclear Instruments and Methods in Physics Research B, 206, p.395 - 398, 2003/05

https://doi.org/10.1016/S0168-583X(03)00770-5

Times Cited Count：9 Percentile：53.35(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Formation of promising Co-C nanocompositions

Lavrentiev, V.; Abe, Hiroaki; Yamamoto, Shunya; Naramoto, Hiroshi; Narumi, Kazumasa

Surface and Interface Analysis, 35(1), p.36 - 39, 2003/01

https://doi.org/10.1002/sia.1489

Times Cited Count：8 Percentile：22.7(Chemistry, Physical)

no abstracts in English

Journal Articles

Formation of carbon nanotubes under conditions of Co+C $_{60}$ film

Lavrentiev, V.; Abe, Hiroaki; Yamamoto, Shunya; Naramoto, Hiroshi; Narumi, Kazumasa

Physica B; Condensed Matter, 323(1-4), p.303 - 305, 2002/10

https://doi.org/10.1016/S0921-4526(02)01031-1

Times Cited Count：15 Percentile：59.47(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Boundary structure of Mo/Si multilayers for soft X-ray mirrors

Ishino, Masahiko; Yoda, Osamu; Haishi, Yasuyuki*; Arimoto, Fumiko*; Takeda, Mitsuhiro*; Watanabe, Seiichi*; Onuki, Somei*; Abe, Hiroaki

Japanese Journal of Applied Physics, Part 1, 41(5A), p.3052 - 3056, 2002/05

https://doi.org/10.1143/JJAP.41.3052

Times Cited Count：12 Percentile：45.92(Physics, Applied)

no abstracts in English

Journal Articles

Effects of annealing and quenching treatments on reconstruction of rutile thin films on sapphire substrates

Choi, Y.; Yamamoto, Shunya; Abe, Hiroaki; Ito, Hisayoshi

Surface Science, 499(2-3), p.203 - 209, 2002/03

https://doi.org/10.1016/S0039-6028(01)01822-2

Times Cited Count：13 Percentile：55.62(Chemistry, Physical)

Morphology change in rutile TiO2 thin films on sapphire substrate prepared by pulsed laser deposition under reduced oxygen envirnment was investigated as a function of film thickness, temperature and cooling treatment with AFM, XRD, and SEM/EDX. In case of 5 nm thick films, morphology strongly deponds on annealing and cooling treatments. Formation model of TiO2 particles on sapphire substrate is proposed based on instability of the substrate at elevated temperature.

Journal Articles