Papers - HAGIHARA Koji
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六方晶系材料にて観察される変形帯の特徴
本浪雅史, 萩原幸司, 伊津野仁史, 多根正和, 山崎倫昭, 眞山剛, 中野貴由, 河村能人
第58回 日本学術会議材料工学連合講演会 講演論文集 333 2014.10
Language：Japanese Publishing type：Research paper (other academic)
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強化相としてのLPSO相が示す塑性異方性
萩原幸司, 岡本拓也, 伊津野仁史, 本浪雅史, 山崎倫昭, 中野貴由, 河村能人
第58回 日本学術会議材料工学連合講演会 講演論文集 325 - 326 2014.10
Language：Japanese Publishing type：Research paper (other academic)
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単結晶による生体用β型チタン合金の交番変形特性解明
萩原幸司
チタン 62 266 2014.10
Language：Japanese Publishing type：Research paper (scientific journal)
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高機能構造材料開発への取り組み Reviewed
萩原幸司
まてりあ（日本金属学会誌） 53 348 - 354 2014.08
Language：Japanese Publishing type：Research paper (scientific journal)
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Control of microstructure and fracture toughness improvement of NbSi2/MoSi2 duplex lamellar silicides by TaC particles dispersion Reviewed
Koji Hagihara, Tatsuya Fushiki, Takayoshi Nakano
SCRIPTA MATERIALIA 82 53 - 56 2014.07
Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD
The floating-zone melting method enabled the dispersion of TaC particles in a C40-(Mo0.85Nb0.15)Si-2 single crystal. By annealing the C40 crystal, coarse C11(b) phases were formed around the TaC particles and the precipitation of the D8(8)-(Mo,Nb,Ta)(5)Si3C phase was also induced, in addition to the development of a C40/C11(b) lamellar microstructure. Such a microstructure containing TaC particles led to a reduction in the orientation dependence of the fracture toughness of duplex silicide crystals. (c) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Highly ordered 10H-type long-period stacking order phase in a Mg-Zn-Y ternary alloy Reviewed
Michiaki Yamasaki, Masafumi Matsushita, Koji Hagihara, Hitoshi Izuno, Eiji Abe, Yoshihito Kawamura
SCRIPTA MATERIALIA 78-79 13 - 16 2014.05
Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD
A highly ordered long-period stacking order (LPSO) structure of 10H-type is found to form in Mg75Zn10Y15 (at.%) alloys annealed at 773 K, with a remarkably developed in-plane long-range order of Zn/Y atoms. The degree of order of the present 10H-LPSO Mg-Zn-Y phase is similar to that of the Mg-Al-Gd alloys, the structural characteristics of which are described according to order/disorder-type intermetallic polytypes. The measured composition Mg77.2Zn9.7Y13.1 appears to be precisely consistent with an ideal stoichiometry of the 10H-Mg23Zn3Y4 (Mg76.7Zn10Y13.3) phase. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Microsructure and mechanical properties of the NbSi2/MoSi2 crystal with lamellar structure Reviewed
K. Hagihara, Y. Hama, T. Fushiki, K. Yuge, T. Nakano
Materials Science Forum 783-786 1123 - 1128 2014.04
Language：English Publishing type：Research paper (scientific journal)
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Ab-initio study of long-period superstructures and anti-phase boundaries in Al-rich gamma-TiAl (L1(0))-based alloys Reviewed
P. S. Ghosh, A. Arya, U. D. Kulkarni, G. K. Dey, S. Hata, T. Nakano, K. Hagihara, H. Nakashima
PHILOSOPHICAL MAGAZINE 94 ( 11 ) 1202 - 1218 2014.04
Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD
In this work, we report first-principles investigation of structural stability of all experimentally observed ordered long-period superstructures (LPSs), viz., r-Al2Ti, h-Al2Ti, Al5Ti3 along with Al5Ti3 ', Al11Ti7 and Al3Ti2 LPSs, which are observed only as short-range ordered clusters at nanoscale level in Al-rich TiAl-based alloys. We adopt a procedure based on space-filling tiling arrangement of ordered Ti2Al, Ti3Al, Ti4Al motifs and their combination along with a symmetry analysis programme to determine the unit cell and the crystallographic information of Al5Ti3 ', Al11Ti7 and Al3Ti2 LPSs in terms of L1(0) fcc unit cell. First-principles calculations are performed to further refine these crystallographic parameters (Wyckoff positions and lattice parameters) obtained from the above procedure. Moreover, it is found that the family of five LPSs have subgroup-supergroup relationships with gamma-TiAl (Sp. gr. P4/mmm) and among themselves. Further, we find the inherent stability of r-Al2Ti + gamma-TiAl and 2Al(5)Ti(3) + gamma-TiAl phase mixtures at 0 K compared to isomolecular Al3Ti2 and Al11Ti7 LPSs at their respective concentrations. The calculations of single-crystal elastic constants of Al5Ti3, Al11Ti7, Al3Ti2 and Al5Ti3 ' LPSs show all these four structures are mechanically stable. We also calculate antiphase boundary (APB) formation energies for two types of APBs, viz., type-A and type-C in ordered Al5Ti3 LPS using the supercell approach. The relaxed APB energies for type-A and type-C APBs are 15.44 and 124.16 mJ/m(2), respectively.
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Development of Microstructures of Long-Period Stacking Ordered Structures in Mg85Y9Zn6 Alloys Annealed at 673 K (400 degrees C) Examined by Small-Angle X-Ray Scattering Reviewed
Hiroshi Okuda, Toshiki Horiuchi, Toshiki Maruyama, Michiaki Yamasaki, Yoshihito Kawamura, Koji Hagihara, Shinji Kohara
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 45A ( 1 ) 147 - 151 2014.01
Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER
Development of LPSO structure and in-plane ordering during annealing the Mg85Y9Zn ternary alloy sample at 673 K (400 degrees C) was examined by synchrotron radiation small-angle scattering/diffraction measurements. By examining the first diffraction peaks for 18R, 10H, and in-plane order spot, the growth kinetics of in-plane order domain and the transition from 10H into 18R were discussed. The domain growth of in-plane order was characterized by small domain with little correlation between neighboring segregation layers. (C) The Minerals, Metals & Materials Society and ASM International 2013
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OS0101 Characteristics of the deformation bands formed in the LPSO phase
HAGIHARA Koji, HONNAMI Masahito, YAMASAKI Michiaki, OKAMOTO Takuya, IZUNO Hitoshi, TANE Masakazu, NAKANO Takayoshi, KAWAMURA Yoshihito
The Proceedings of the Materials and Mechanics Conference 2014 ( 0 ) _OS0101 - 1_-_OS0101-2_ 2014
Language：Japanese Publishing type：Research paper (other academic) Publisher：The Japan Society of Mechanical Engineers
Formation of curious deformation bands has been reported as one of the deformation mechanisms occurring in a Mg-based long period stacking ordered (LPSO) phase. The origin of the deformation band is still unknown, and the possibility of the deformation kink band and/or the deformation twin has been discussed. To clarify this, the crystallographic nature of deformation bands formed in the LPSO phase was examined by scanning electron microscope-electron backscatter diffraction (SEM-EBSD) pattern analysis. The deformation band in the LPSO phase was found to show three arbitrariness on its crystallographic nature: an ambiguous crystal rotation axis that varied on the [0001] zone axis from band to band; an arbitral crystal rotation angle that was not fixed and showed relatively wide distributions; and a variation in crystal rotation angle depending on the position even within a deformation band boundary itself. These features were coincident with those observed in the deformation bands formed in Zn polycrystals, suggesting that the formed deformation bands in LPSO phase crystals are mainly deformation kink bands.
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Interface migration with segregation in MoSi<inf>2</inf>-based lamellar alloy simulated by phase-field method Reviewed
Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki Inui
Advanced Materials Research 922 832 - 837 2014
Language：English Publishing type：Research paper (international conference proceedings)
MoSi2-based alloys are attracting attention as ultra-high temperature structural material for super-high efficiency gas turbine power generation systems. In this study, the effects of Cr- and Zr-addition on interface migration in MoSi2/NbSi2 lamellar silicide were examined by phase-field simulations employing the segregation energies evaluated by the first principles calculation in addition to thermodynamic free energy in order to take into account the chemically-driven interfacial segregation. The simulation results indicate that both Cr and Zr can segregate at the lamellar interface to suppress its migration, and the Zr-addition is more effective to lower the interface migration rate than the Cr-addition owing to its higher segregation energy. © (2014) Trans Tech Publications, Switzerland.
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Microstructure and mechanical properties of NbSi2/MoSi2 crystals with lamellar structure Invited Reviewed International journal
Koji Hagihara, Yoichiro Hama, Tatsuya Fushiki, Koretaka Yuge, Takayoshi Nakano
Materials Science Forum 783-786 1123 - 1128 2014
Language：English Publishing type：Research paper (international conference proceedings) Publisher：Trans Tech Publications Ltd
NbSi2/MoSi2 duplex silicide crystals are potentially a new-class of ultra-high temperature structural materials. Improvement in the thermal stability of their lamellar microstructure was accomplished by the addition of a minute amount of either Cr or Zr. The mechanical properties of the duplex silicide, such as fracture toughness and high temperature strength, show strong orientation dependence, thereby suggesting the importance of the control of microstructure to improve their properties. © (2014) Trans Tech Publications, Switzerland.
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Mg基シンクロ型LPSO相の塑性変形機構、Mg合金強化に及ぼす寄与 Invited
萩原幸司, 山崎倫昭, 中野貴由, 河村能人
第57回 日本学術会議材料工学連合講演会 講演論文集 2013.11
Language：Japanese Publishing type：Research paper (other academic)
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Cr segregation at C11(b)/C40 interface in MoSi2-based alloys: A first-principles study Reviewed
Koretaka Yuge, Kyosuke Kishida, Haruyuki Inui, Yuichiro Koizumi, Koji Hagihara, Takayoshi Nakano
INTERMETALLICS 42 165 - 169 2013.11
Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD
Based on the first-principles calculation, we investigated Cr segregation behavior at the C11(b)/C40 lamellar interface for MoSi2-based alloys. We first elucidated the energetically stable interface structure among possible contacts between C11(b) and C40, where the interface energy is 1.7 meV/angstrom(2). Without inclusion of lattice vibrational contribution to segregation energy, Cr composition at the interface was lower than that at C40 phase, which was inconsistent with the early experimental result. Inclusion of the vibrational contribution successfully resulted in strong Cr segregation at the interface over that at C11(b) as well as C40 phase. This indicates that Cr segregation at the most stable interface is a thermodynamically stable state, in which lattice vibration plays a significant role. (C) 2013 Elsevier Ltd. All rights reserved.
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Possibility of Mg- and Ca-based intermetallic compounds as new biodegradable implant materials Reviewed
Koji Hagihara, Kenta Fujii, Aira Matsugaki, Takayoshi Nakano
MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS 33 ( 7 ) 4101 - 4111 2013.10
Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV
Mg- or Ca-based intermetallic compounds of Mg2Ca, Mg2Si, Ca2Si and CaMgSi are investigated as possible new candidates for biodegradable implant materials, attempting to improve the degradation behavior compared to Mg and Ca alloys. The reactivity of Ca can be indeed reduced by the formation of compounds with Mg and Si, but its reactivity is still high for applications as an implant material. In contrast, Mg2Si shows a higher corrosion resistance than conventional Mg alloys while retaining biodegradability. In cytotoxicity tests under the severe condition conducted in this study, both pure Mg and Mg2Si showed relatively high cytotoxicity on preosteoblast MC3T3-E1. However, the cell viability cultured in the Mg2Si extract medium was confirmed to be better than that in a pure Mg extract medium in all the conditions investigated with the exception of the 10% extract medium, because of the lower corrosion rate of Mg2Si. The cytotoxicity derived from the Si ion was not significantly detected in the Mg2Si extract medium in the concentration level of -70 mg/l measured in the present study. For aiming the practical application of Mg2Si as an implant material, however, its brittle nature must be improved. (C) 2013 Elsevier B.V. All rights reserved.
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Elastic properties of an Mg-Zn-Y alloy single crystal with a long-period stacking-ordered structure Reviewed
M. Tane, Y. Nagai, H. Kimizuka, K. Hagihara, Y. Kawamura
ACTA MATERIALIA 61 ( 17 ) 6338 - 6351 2013.10
Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD
The elastic properties of an Mg85Zn6Y9 (at.%) alloy single crystal with a long-period stacking-ordered (LPSO) structure, synchronized with periodic enrichment of Zn and Y atoms, were investigated, the properties having remained unclear because of the difficulty in growing large single crystals. Directionally solidified (DS) Mg85Zn6Y9 alloy polycrystals consisting of a single phase of the 18R-type LPSO structure were prepared using the Bridgman technique. For the DS polycrystals, a complete set of elastic constants was measured with resonant ultrasound spectroscopy combined with electromagnetic acoustic resonance, in which the texture formed by the directional solidification was taken into account. By analyzing the elastic stiffness of DS polycrystals on the basis of a newly developed inverse Voigt Reuss Hill approximation, the elastic stiffness components of the single-crystalline LPSO phase were determined. It was revealed that the Young's modulus of the LPSO phase along (00 01) in the hexagonal expression was clearly higher than that along < 1 1 (2) over bar0 >, and the Young's modulus and shear modulus were clearly higher than those of pure magnesium. These findings were validated by first-principles calculations based on density functional theory. Analyses by first-principles calculations and micromechanics modeling indicated that the long periodicity of the 18R-type stacking structure hardly enhanced the elastic modulus, whereas the Zn/Y-enriched atomic layers, containing stable short-range ordered clusters, exhibited a high elastic modulus, which contributed to the enhancement of the elastic modulus of the LPSO phase in the Mg-Zn-Y alloy. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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シンクロ型LPSO相におけるキンク変形帯の結晶学的特徴 Invited
萩原幸司
日本機械学会 2013年度年次大会 講演論文集 OS-0415 2013.09
Language：Japanese Publishing type：Research paper (other academic)
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Deformation behavior of LPSO phase and Zn accompanied by kink band formation Reviewed
K. Hagihara, Y. Fukusumi, M. Yamasaki, R. Matsumoto, M. Honnami, H. Izuno, T. Nakano, Y. Kawamura
Proc. of PRICM8 973 - 978 2013.08
Language：English Publishing type：Research paper (scientific journal)
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Non-basal slip in Ni-3(Ti, Nb) and Ni-3(Ti, Al) single crystals with various long-period stacking ordered structures Reviewed
Koji Hagihara, Tetsunori Tanaka, Hitoshi Izuno, Yukichi Umakoshi, Takayoshi Nakano
ACTA MATERIALIA 61 ( 12 ) 4365 - 4373 2013.07
Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD
Variations in operative non-basal slip systems in Ni3Ti-based long-period stacking ordered (LPSO) phases with the stacking sequence of the closely packed planes and the temperature dependence of the critical resolved shear stress (CRSS) were investigated. It was confirmed that the {(1) over bar 100} prism slip is operative in most of the LPSO phases with hexagonal unit cells, while the {(1) over bar 011} pyramidal slip is operative in 9R LPSO phase with rhombohedral unit cell. The mechanism controlling the deformation by non-basal slip at low temperatures is considered to be governed by the energy of the antiphase boundary (APB) formed between the a/6 < 11 (2) over bar0 > superpartial dislocations in accordance with the kink pair nucleation mechanism proposed by Mitchell et al. The dependence of variations in CRSS for non-basal slip on the Nb content was found to be much smaller than that for basal slip. The present results suggest that the mobility of dislocations on the non-basal plane hardly affected the behavior of yield stress anomalies (YSAs) caused by basal slip in Ni-based LPSO phases, although the Kear-Wilsdorf locking process, which is responsible for the YSA by basal slip, accompanies microscopic cross-slip from the basal slip plane onto the non-basal planes. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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1400℃に耐える合金 International journal
萩原幸司, 中野貴由
Ceramics Japan 48 555 2013.06
Language：Japanese Publishing type：Research paper (scientific journal)
