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-base GdO
precipitations in a Mg-Zn-Gd alloyIto, Yuto*; Egusa, Daisuke*; Yamaguchi, Masatake; Abe, Eiji*
Materials Transactions, 64(8), p.2022 - 2025, 2023/08
Times Cited Count：0 Percentile：0(Materials Science, Multidisciplinary)We have found that, during 
scanning transmission electron microscopy observations, heating of a Mg
Zn
Gd
(at.%) alloy at 623K leads to dynamic precipitations of face-centered-cubic ()-based Gd nanoparticles. With the aid of density-functional theory (DFT) calculations, the observed lattice constant of 5.32
, which is larger than that expected for pure -Gd of 5.06, is likely to be due to oxygen atoms inserted at tetrahedral interstitial sites with essentially a fractional occupation. Systematic DFT calculations show possible occurrences of -Gd-based oxide phase with a wide non-stoichiometry range by occupying either tetrahedral or octahedral interstitial positions, being represented as GdO.
Zn
Y
alloy using X-ray photoelectron spectroscopyMiyazaki, Hidetoshi*; Akatsuka, Tatsuyoshi*; Kimura, Koji*; Egusa, Daisuke*; Sato, Yohei*; Itakura, Mitsuhiro; Takagi, Yasumasa*; Yasui, Akira*; Ozawa, Kenichi*; Mase, Kazuhiko*; et al.
Materials Transactions, 64(6), p.1194 - 1198, 2023/06
Times Cited Count：1 Percentile：54.26(Materials Science, Multidisciplinary)We investigated the electronic structure of the MgZnY alloy using hard and soft X-ray photoemission spectroscopy and electronic band structure calculations to understand the mechanism of the phase stability of this material. Electronic structure of the MgZnY alloy showed a semi-metallic electronic structure with a pseudo-gap at the Fermi level. The observed electronic structure of the MgZnY alloy suggests that the presence of a pseudogap structure is responsible for phase stability.
Urakawa, Yutaka*; Egusa, Daisuke*; Itakura, Mitsuhiro; Abe, Eiji*
Materials Transactions, 64(5), p.1065 - 1071, 2023/05
Times Cited Count：0 Percentile：0(Materials Science, Multidisciplinary)Sato, Yohei*; Egusa, Daisuke*; Miyazaki, Hidetoshi*; Kimura, Koji*; Itakura, Mitsuhiro; Terauchi, Masami*; Abe, Eiji*
Materials Transactions, 64(5), p.950 - 954, 2023/05
Times Cited Count：1 Percentile：54.26(Materials Science, Multidisciplinary)Dilute Mg-Zn-Y alloy with a mille-feuille structure (MFS) exhibits a mechanical strength comparable to Mg-Zn-Y alloy with long period stacking/ordered (LPSO) structure through kink deformation. In order to deepen understanding the thermal stability of the MFS-type Mg alloys, it is required to clarify the solute cluster structures composed of Zn and Y in solute enriched stacking faults (SESFs). In this study, electron energy-loss and energy dispersive X-ray spectroscopy based on scanning transmission electron microscopy (STEM-EELS/EDS) were conducted to investigate the electronic structure and composition of Zn and Y in the SESFs of the MFS-Mg alloy. Zn-L2,3 spectra indicated that the valence charges of Zn in the dilute Mg alloy were different from that of the LPSO-type Mg-Zn-Y alloy. In addition, the intensity ratio of L3/L2 in Y-L2,3 spectrum of the dilute MFS-Mg alloy was larger than that of the LPSO-Mg alloy, reflecting the electron occupancies of 4d3/2 and 4d5/2 orbitals of Y atoms were different from those of the LPSO-Mg alloys. STEM-EELS analysis of the SESF composition in the dilute MFS-Mg alloy indicated that the Zn/Y ratio should be lower than that of the LPSO-Mg alloy, which was confirmed also by STEM-EDS measurements. These results indicate that the cluster structure in the SESFs of the dilute MFS-Mg alloy should be different from the ideal Zn6Y8 cluster in the LPSO-type Mg-Zn-Y alloys.
Itakura, Mitsuhiro; Yamaguchi, Masatake; Egusa, Daisuke*; Abe, Eiji*
Materials Transactions, 64(4), p.813 - 816, 2023/04
Times Cited Count：2 Percentile：54.26(Materials Science, Multidisciplinary)
-Mg alloys based on peak asymmetry analysisEgusa, Daisuke*; Manabe, Ryo*; Kawasaki, Takuro; Harjo, S.; Sato, Shigeo*; Abe, Eiji*
Materials Today Communications (Internet), 31, p.103344_1 - 103344_6, 2022/06
Times Cited Count：8 Percentile：66.14(Materials Science, Multidisciplinary)Itakura, Mitsuhiro; Yamaguchi, Masatake; Egusa, Daisuke*; Abe, Eiji*
Acta Materialia, 203, p.116491_1 - 116491_9, 2021/01
Times Cited Count：23 Percentile：88.82(Materials Science, Multidisciplinary)Solute cluster in LPSO alloys plays a key role in their idiosyncratic plastic behavior such as kink formation and kink strengthening. Identifying the atomistic details of the cluster structure is a prerequisite for any atomistic modeling of LPSO alloys aiming for their improved strength and ductility, but there have been uncertainty about interstitial atom in the cluster. While density functional theory calculations have shown that inclusion of interstitial atom is energetically favorable, it has been unclear how the extra atom is provided, how much of the cluster have interstitial atoms, and what kind of element they are. In the present work we use density functional theory calculations to investigate the growth process of the solute cluster, specifically that of Mg-Y-Zn LPSO alloy, to determine the precise atomistic structure of solute cluster. We show that a pair of an interstitial atom and a vacancy is spontaneously created when a certain number of solute atoms are absorbed into the cluster, and all the full-grown cluster should include interstitial atom. We also show that interstitial atom is either Mg or Y atom, while Zn interstitial atom is extremely rare. These knowledge greatly simplifies atomistic modeling of solute clusters in Mg-Y-Zn alloy. Owing to the vacancies emitted from the cluster, vacancy density should be over-saturated in regions where solute clusters are growing, and the increased vacancy density accelerates cluster growth.
Itakura, Mitsuhiro; Yamaguchi, Masatake; Egusa, Daisuke*; Abe, Eiji*
no journal, ,
To predict the distributions of interstitial atoms in the solute clusters in LPSO alloys, and to determine the kind of elements present, it is necessary to identify mechanisms by which interstitial atoms are created. In the present work, we use density functional theory calculations to investigate growth processes of solute clusters, in order to determine the precise atomistic structure of its solute clusters. We show that a pair of an interstitial atom and a vacancy are spontaneously created when a certain number of solute atoms are absorbed into the cluster, and that all full-grown clusters should include interstitial atoms. We also demonstrate that interstitial atoms are mostly Mg, while the rest are Y; interstitial Zn atoms are negligible. This knowledge greatly simplifies the atomistic modeling of solute clusters in Mg-Y-Zn alloys.
Egusa, Daisuke*; Zhao, Y.*; Saito, Hikaru*; Hata, Satoshi*; Itakura, Mitsuhiro; Abe, Eiji*
no journal, ,
no abstracts in English
Hiyoshi, Kensuke*; Egusa, Daisuke*; Yamaguchi, Masatake; Abe, Eiji*
no journal, ,
no abstracts in English
Ito, Yuto*; Egusa, Daisuke*; Yamaguchi, Masatake; Abe, Eiji*
no journal, ,
no abstracts in English
Itakura, Mitsuhiro; Yamaguchi, Masatake; Egusa, Daisuke*; Abe, Eiji*
no journal, ,
Ito, Yuto*; Egusa, Daisuke*; Yamaguchi, Masatake; Abe, Eiji*
no journal, ,
no abstracts in English
Ito, Yuto*; Egusa, Daisuke*; Yamaguchi, Masatake; Abe, Eiji*
no journal, ,
no abstracts in English
Ito, Yuto*; Egusa, Daisuke*; Yamaguchi, Masatake; Abe, Eiji*
no journal, ,
Among HCP metals, Zn and Cd, which exhibit high c/a ratios, exhibit a peculiar deformation mode with crystal rotation called kink deformation under conditions where the main slip system is suppressed. Although a model of kink deformation has been proposed based on collective rearrangement of dislocations, the details of the kink deformation have not been clarified. In this study, we evaluate the phonon dispersion relation using first-principles calculations for HCP metals under uniaxial compression in the basal plane, where kink deformation is known to occur, and verify the generalized stacking fault energy, which is considered important for characterization of dislocations.
Saegusa, Yu; Nishino, Saki; Horie, Koji; Yatabe, Hitoshi; Yamada, Takashi; Oyama, Daisuke; Uchida, Naoki
no journal, ,
All the spent fuel stored in the Tokai Reprocessing Plant is transported to the overseas reprocessing plant. When spent fuel transportation, we use dry type cask instead of wet type cask. Therefore, equipment of the wet type cask is not used. And the equipment is some possibility of interfere with cask because the equipment is stored in the transport route. So, we were dismantled receiving and storage process equipment as preparation work for spent fuel transportation. In dismantlement work, we selected cutting equipment after scrutinizing size and shape of equipment, contamination and workability. Moreover, we have taken safety measures during work such as fire prevention and contamination control. As a result, the work was completed as originally planned.
Ito, Yuto*; Egusa, Daisuke*; Yamaguchi, Masatake; Abe, Eiji*
no journal, ,
Among hcp metals, Zn and Cd, which have high c/a ratios, exhibit kink deformation characterized by crystal rotation under conditions of suppressed basal slip under in-basal compression. Kink deformation has recently attracted attention because it compensates for the plastic deformation of the hcp structure, which has a limited independent slip system, and also contributes to high strength in some Mg alloys. In this study, we evaluated the structural stability of hcp metals under uniaxial compression conditions where basal slip is suppressed, using first-principles calculations of the Phonon dispersion relation and generalized stacking fault energy (GSFE) to understand the kink deformation mechanism.
