論文 - 萩原 幸司
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Dynamic recovery around deformation kink boundary of Mg-Y-Zn alloy with long-period stacking ordered structure 査読あり 国際誌
Michiaki Yamasaki, Tsubasa Matsumoto, Tsuyoshi Mayama, Hidetoshi Somekawa, Koji Hagihara, Soya Nishimoto, Yoshihito Kawamura
Materials Letters 377 2024年09月
記述言語：英語 掲載種別：研究論文（学術雑誌）
This study demonstrated the possibility of dynamic recovery by forming a kink boundary in the long-period stacking ordered phase of the Mg85Y9Zn6 (at%) alloy. The compressive deformation at 1 % strain on the double-notched directionally solidified specimen produced three regions; undeformed, deformed, and kink-deformed regions. A nanoindenter was applied to three different regions. The deformed region sufficiently far from the kink boundary exhibited a 26 % higher nanoindentation hardness than the undeformed region owing to work-hardening, whereas the hardness decreased when approaching the kink boundary. At 1 μm or less from the kink boundary, the magnitude of hardness recovered to the same level as the undeformed region. This observation implies a “recovery kink zone” because of the dynamic recovery associated with kink boundary formation.
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Effects of multimodal microstructure on fracture toughness and its anisotropy of LPSO-type extruded Mg-1Zn-2Y alloys 査読あり 国際誌
Soya Nishimoto, Taiga Yasuda, Koji Hagihara, Michiaki Yamasaki
Journal of Magnesium and Alloys 12 2952 - 2966 2024年07月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
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High-temperature strength and kink-band formation in mille-feuille-structured Ti/FeTi eutectic alloys 査読あり 国際誌
Toko Tokunaga, Takuya Yonemura, Koji Hagihara
Materials Science and Engineering A 900 146505 - 146505 2024年04月
担当区分：最終著者, 責任著者 記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
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Effect of Rolling and Alloying Elements on the Impact Properties of Hypereutectoid Steels 査読あり 国際誌
Toko Tokunaga, Yoritoshi Minamino, Koji Yamamoto, Toshiyuki Sugimoto, Koji Hagihara
ISIJ International 64 ( 6 ) 1078 - 1088 2024年04月
担当区分：最終著者, 責任著者 記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Iron and Steel Institute of Japan
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Creep deformation behavior and microstructure of α-Mg/long-period stacking ordered (LPSO) duplex Mg-Y-Zn alloy prepared by hot extrusion and heat treatment 査読あり 国際誌
Takahiro Mineta, Daisuke Takahashi, Wataru Bando, Hiroyuki Sato, Koji Hagihara, Michiaki Yamasaki
Materials Today Communications 39 108912 - 108912 2024年04月
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New kink-band formation mechanism discovered in Zn-Al alloy with mille-feuille microstructure 査読あり 国際誌
Koji Hagihara, Shuhei Ohsawa, Toko Tokunaga
Materials and Design 239 112767 - 112767 2024年02月
担当区分：筆頭著者, 責任著者 記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
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Stress-induced symmetrical tilt boundaries in layer-structured Al-Cu eutectic alloys 査読あり
Daisuke Egusa, Tsuyoshi Mayama, Koji Hagihara, Eiji Abe
Scripta Materialia 244 116025 2024年02月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Effects of cementite particles on impact properties in high-hardness hypereutectoid steels 査読あり
T. Tokunaga , K. Yamamoto , Y. Minamino , T. Takayama , T. Sugimoto , K. Hagihara
ISIJ International 64 389 - 400 2024年01月
担当区分：最終著者, 責任著者 記述言語：英語 掲載種別：研究論文（学術雑誌）
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Local Plastic Deformation of Kink Band Opposing External Stress in Mg–Zn–Y Alloy 査読あり 国際誌
Ryutaro Matsumura, Yuri Ueda, Koji Hagihara, Yuri Shinohara, Tomonari Inamura
Materials Transactions 65 ( 1 ) 101 - 104 2024年01月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japan Institute of Metals
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Contributions of multimodal microstructure in the deformation behavior of extruded Mg alloys containing LPSO phase 査読あり 国際誌
Koji Hagihara, Tsuyoshi Mayama, Michiaki Yamasaki, Stefanus Harjo, Toko Tokunaga, Kazuki Yamamoto, Mika Sugita, Kairi Aoyama, Wu Gong, Soya Nishimoto
International Journal of Plasticity 173 103865 2023年12月
担当区分：筆頭著者, 責任著者 記述言語：英語 掲載種別：研究論文（学術雑誌）
The unique control mechanisms of the plastic deformation of two-phase extruded alloy composed of Mg and long-period stacking ordered (LPSO) phase were clarified by comparison with those of other Mg solid-solution alloys, focusing on the question “why do the Mg/LPSO two-phase alloys exhibit both large elongation and high strength?”. The stress-strain curves for each grain in the alloys could be imaginary estimated using neutron diffraction analysis during the tensile test. The results demonstrate that the deformation behaviors of the worked and recrystallized grains are significantly different in all the Mg-extruded alloys owing to the strong plastic anisotropy in Mg with hexagonal close-packed (hcp) structure. Therefore, the deformation behavior is controlled by a composite-like deformation mechanism, even in single-phase Mg solid-solution alloys. In Mg-Y-Zn ternary alloys, the recrystallized Mg grains exhibited significant lattice softening at the initial stage of yielding owing to the escape of basal dislocations from the Y/Zn dragging atmosphere. However, the worked grains acted as strengthening components. In the Mg/LPSO two-phase alloy, the composite-like deformation behavior was enhanced, and the LPSO phase significantly contributed to the strengthening of the alloy. Moreover, it was hypothesized that the LPSO phase contributes not only to the alloy's strength but also to its elongation by increasing the work-hardening rate. We proposed the new concept “Anisotropic Mechanical property-Induced Ductilization (AMID)” by multimodal microstructure, to explain this phenomenon. As the physical origin for inducing AMID, kink-band strengthening in the LPSO phase is believed to be one of the reasons for the increase in the work-hardening rate of the extruded LPSO-phase grains in the Mg/LPSO two-phase alloy, resulting in an improved ductility.
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Verifcation of Rank-1 Connection Model of Kink Band in Mg–Zn–Y Alloy 査読あり
Ryutaro Matsumura, Koji Hagihara, Tomonari Inamura
Materials Transactions 65 97 - 100 2023年11月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Modification of grain boundary microstructure by controlling dissolution behavior of θ particles in Cr-containing hypereutectoid steel 査読あり
Koji Yamamoto , Takemori Takayama , Yoritoshi Minamino , Yuichiro Koizumi , Toko Tokunaga , Koji Hagihara
Materials Characterization 205 113241 2023年10月
担当区分：最終著者, 責任著者 記述言語：英語 掲載種別：研究論文（学術雑誌）
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Development of Zn–Mg–Ca Biodegradable Dual-Phase Alloys 査読あり
Koji Hagihara , Shuhei Shakudo , Toko Tokunaga , Takayoshi Nakano
Metals 13 ( 6 ) 1 - 13 2023年06月
担当区分：筆頭著者, 責任著者 記述言語：英語 掲載種別：研究論文（学術雑誌）
DOI： 10.3390/met1306109
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Investigation of the electronic structure of the Mg99.2Zn0.2Y0.6 alloy using X-ray photoelectron spectroscopy 査読あり
Hidetoshi Miyazaki , Tatsuyoshi Akatsuka , Koji Kimura , Daisuke Egusa , Yohei K. Sato , Mitsuhiro Itakura , Yasumasa Takagi , Akira Yasui , Kenichi Ozawa , Kazuhiko Mase , Toko Tokunaga , Kouichi Hayashi , Koji Hagihara , Eiji Abe
Materials Transactions 64 1194 - 1198 2023年06月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Effect of short-range order on the high-temperature plastic deformation behavior of Ni–Cr–W, Ni–W, and Ni–Re single crystals 査読あり
Koji Hagihara
Journal of Materials Science and Technology 165 143 - 152 2023年05月
担当区分：筆頭著者, 責任著者 記述言語：英語 掲載種別：研究論文（学術雑誌）
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Local structural analysis around solute-element in annealed Mg99.2Zn0.2Y0.6 alloy using X-ray fluorescence holography 査読あり
Koji Kimura , Daisuke Egusa , Koji Hagihara , Naohisa Happo , Naomi Kawamura , Hiroo Tajiri , Kouichi Hayashi , Eiji Abe
Materials Transactions 64 750 - 755 2023年04月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Synchronized Formation of Kink Bands in Al/Al2Cu Mille-Feuille Structured Alloy 査読あり
Takayuki Shiraiwa , Naoya Hamada , Fabien Briffod , Manabu Enoki , Koji Hagihara
Materials Transactions 64 735 - 743 2023年04月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Relationship between Cluster-Arranged Nanoplate Formation and Mechanical Properties of Dilute Mg–Y–Zn Alloys Prepared by Combination of Low-Cooling-Rate Solidification and Extrusion Techniques 査読あり
Seitaro Ishizaki , Michiaki Yamasaki , Koji Hagihara , Soya Nishimoto , Taisuke Nakamura , Yoshihito Kawamura
Materials Transactions 64 756 - 765 2023年04月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Unified Understanding of Strengthening Mechanisms Acting in Mg/LPSO Two-Phase Extruded Alloys with Varying LPSO Phase Volume Fraction 査読あり
Koji Hagihara , Toko Tokunaga , Kazuki Yamamoto , Michiaki Yamasaki , Tsuyoshi Mayama , Takumi Shioyama , Yoshihito Kawamura , Takayoshi Nakano
Materials Transactions 64 720 - 729 2023年04月
担当区分：筆頭著者, 責任著者 記述言語：英語 掲載種別：研究論文（学術雑誌）
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Impact of gas flow direction on the crystallographic texture evolution in laser beam powder bed fusion 査読あり 国際共著
Hiroki Amano , Takuya Ishimoto , Koji Hagihara , Ryoya Suganuma , Keisuke Aiba , Shi-Hai Sun , Pan Wang , Takayoshi Nakano
Virtual and Physical Prototyping 18 2023年02月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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回折法を利用したLPSO型マグネシウム合金における 階層的変形機構に関する研究 査読あり
城 鮎美，菖蒲 敬久，萩原 幸司，渡邉 真史
SPring-8/SACLA 利用研究成果集 10 ( 5 ) 438 - 446 2022年11月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
DOI： 10.18957/rr.10.5.438
その他リンク： https://www.jstage.jst.go.jp/article/springresrep/10/5/10_438/_article/-char/ja/
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Kink-band formation in the directionally-solidified Mg/LPSO two-phase alloys 招待あり 査読あり 国際誌
Toko Tokunaga, Koji Hagihara, Michiaki Yamasaki, Tsuyoshi Mayama, Kazuki Yamamoto, Hiroki Narimoto, Taiki Kida, Yoshihito Kawamura, Takayoshi Nakano
Science and Technology of Advanced Materials 23 ( 1 ) 752 - 766 2022年11月
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Microstructural factors governing the significant strengthening of Al/Al2Cu mille-feuille structured alloys accompanied by kink-band formation 査読あり 国際共著
K. Hagihara, T. Tokunaga, S. Ohsawa, S. Uemichi, K. Guan, D. Egusa, E.Abe
International Journal of Plasticity 158 103419 2022年09月
担当区分：筆頭著者 記述言語：英語 掲載種別：研究論文（学術雑誌）
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α-Mg/LPSO (Long-Period Stacking Ordered) phase interfaces as obstacles against dislocation slip in as-cast Mg-Zn-Y alloys 査読あり 国際共著
T. Mayama, S. R. Agnew, K. Hagihara, K. Kamura, K. Shiraishi, M. Yamasaki, Y. Kawamura
International Journal of Plasticity 154 103294 2022年03月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Anisotropic control of crystallographic texture in metals and ceramics powder-bed-fusion-type additive manufacturing―A review 招待あり 査読あり 国際誌
K. Hagihara, T. Nakano
Journal of Metals (JOM) 74 1760 - 1773 2021年11月
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Change in elastic properties during room-temperature aging in body-centered cubic Mg-Li and Mg-Li-Al single crystals 査読あり 国際共著 国際誌
R. Liu, S. Higashino, K. Hagihara, L. Zhang, T. Sekino, M. Tane
Journal of Materials Science & Technology 109 49 - 53 2021年11月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
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Comparison of microstructure, crystallographic texture, and mechanical properties in Ti–15Mo–5Zr–3Al alloys fabricated via electron and laser beam powder bed fusion technologies 査読あり 国際共著 国際誌
S.-H. Sun, K. Hagihara, T. Ishimoto, R. Suganuma, Y.-F. Xue, T. Nakano
Additive Manufacturing 47 102329 2021年10月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
Depending on the application, establishing a strategy for selecting the type of powder bed fusion technology—
from electron beam (EB-PBF) or laser powder bed fusion (L-PBF)—is important. In this study, we
focused on the β-type Ti–15Mo–5Zr–3Al alloy (expected for hard-tissue implant applications) as a model material,
and we examined the variations in the microstructure, crystallographic texture, and resultant mechanical
properties of specimens fabricated by L-PBF and EB-PBF. Because the melting mode transforms from the conduction
mode to the keyhole mode with an increase in the energy density in L-PBF, the relative density of the LPBF-
built specimen decreases at higher energy densities, unlike that of the EB-PBF-built specimen. Although both
EB-PBF and L-PBF can obtain cubic crystallographic textures via bidirectional scanning with a 90◦ rotation in
each layer, the formation mechanisms of the textures were found to be different. The <100> texture in the build
direction is mainly derived from the vertically grown columnar cells in EB-PBF, whereas it is derived from the
vertically and horizontally grown columnar cells in L-PBF. Consequently, different textures were developed via
bidirectional scanning without rotation in each layer: the <110> and <100> aligned textures along the build
direction in L-PBF and EB-PBF, respectively. The L-PBF-built specimen exhibited considerably better ductility,
but slightly lower strength than the EB-PBF-built specimen, under the conditions of the same crystallographic
texture and relative density. We attributed this to the variation in the microstructures of the specimens; the
formation of the α-phase was completely absent in the L-PBF-built specimen. The results demonstrate the
importance of properly selecting the two technologies according to the material and its application. -
Quantitative estimation of kink-band strengthening in an Mg–Zn–Y single crystal with LPSO nanoplates 査読あり 国際誌
K. Hagihara, R. Ueyama, T. Tokunaga, M. Yamasaki, Y. Kawamura, T. Nakano
Materials Research Letters 9 467 - 474 2021年09月
担当区分：筆頭著者 記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Taylor and Francis
Kink-band strengthening was first quantitatively evaluated using an Mg–Zn–Y single crystal containing
long-period stacking ordered (LPSO) nanoplates. The ability of a kink-band boundary to act
as a barrier that hinders the motion of dislocations is high and comparable to that of a general random
grain boundary. Nevertheless, a kink-band boundary is regarded as a simple tilt boundary in
the dislocation model. One reason for the anomalous ability of kink-band boundary acting as barriers
is related to its peculiar hierarchical structure, in which many small kink bands with high crystal
rotation angles accumulate in a localized region. -
Control of kink-band formation in mille-feuille structured Al/Al2Cu eutectic alloys 査読あり 国際誌
K. Hagihara, T. Tokunaga, K. Nishiura, S. Uemichi, S. Ohsawa
Materials Science & Engineering A 825 141849 2021年08月
担当区分：筆頭著者 記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
Kink bands have recently received significant attention owing to their ability to increase the strength and
ductility of some Mg alloys. In this study, we first demonstrated that it is also expected even in Al alloys, by
controlling the morphology of the introduced kink bands. Several directionally solidified Al–Cu alloys, wherein
an Al/Al2Cu eutectic lamellar microstructure developed, were focused, and the variations in deformation
behavior with microstructure were examined. The alloys can be deformed at room temperature, and the yield
stress exhibits strong anisotropy. A high yield stress appears when stress is applied parallel to the lamellar
interface, accompanied by kink-band formation. The microstructure was found to play an important role in
controlling kink-band formation and the resultant mechanical properties. Only a few large kink bands form in a
eutectic alloy specimen with a full lamellar microstructure, which is accompanied by a lower yield stress. Thus,
the kink band cannot be used positively in it. In hypoeutectic alloys in which primary Al grains coexist with the
lamellar microstructure, however, significantly high yield stresses appear, which are accompanied by the homogeneous
formation of small kink bands. The results demonstrate that microstructural control can vary the role
of the deformation kink band from the fracture (buckling) mode to the deformation mode via the change in its
morphology. This enables a large increase in yield stress while maintaining the ductility of the Al/Al2Cu eutectic
alloy. The high yield stress is maintained at temperatures up to ~300 ◦C owing to the high thermal stability of
the lamellar microstructure. These findings provide new ways to develop novel high-temperature high-strength
Al alloys. -
Intrinsic kink bands strengthening induced by several wrought-processes in Mg-Y-Zn alloys containing LPSO phase 査読あり 国際誌
H. Somekawa, D. Ando, K. Hagihara, M. Yamasaki, Y. Kawamura
Materials Characterization 825 141849 2021年08月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
The kink bands strengthening effect was investigated using Mg-9at.%Y-6at.%Zn alloys produced by caliber
rolling or extrusion at intermediate and elevated temperatures (373 K and more than 673 K). The results of
microstructural observations showed that deformation kink bands were induced in all the alloys, regardless of
the wrought-processing method and the processing temperatures. Micro-Vickers hardness tests showed that the
regions including kink bands exhibited a higher hardness than those without kink bands, which reveal intrinsic
kink bands strengthening. Interestingly, the trend of this kink bands strengthening effect could be expressed by
an empirical relationship, which was divided into two lines associated with the wrought-processing temperature.
This tendency did not appear to depend on the wrought-processing method. The alloys produced at the intermediate
temperature showed markedly superior hardness, since, in addition to the kink bands strengthening, the
residual strains/dislocations around kink boundaries contributed to obstruct dislocation slips. -
Factor which governs the feature of texture developed during additive manufacturing; clarified from the study on hexagonal C40-NbSi2 査読あり 国際誌
K. Hagihara, T. Ishimoto, M. Suzuki, R. Ozasa, A. Matsugaki, P. Wang, T. Nakano
Scripta materialia 203 114111 2021年07月
担当区分：筆頭著者 記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
C40-NbSi 2 with a hexagonal unit cell is focused as a high-temperature structural material. We first at- tempted the fabrication of the bulk C40-NbSi 2 products via selective laser melting (SLM) in additive manufacturing (AM) process. Strong crystallographic texture control wherein < 0 0 01 > was parallel to the building direction, i.e. development of the so-called basal fiber texture, was achieved in this study. The texture developed in products does not largely vary by changing the scanning strategy, unlike the tex- tures of C11 b -MoSi2 with a tetragonal unit cell and a β-Ti alloy with a cubic unit cell. A comparison of these results led us to the conclusion that crystal symmetry, i.e., the multiplicity of the preferential crys- tal growth direction, is one of the primary factors that governs the features of the textures developed in AM-built materials.
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Ultrahigh specific strength in a magnesium alloy strengthened by spinodal decomposition 査読あり 国際共著 国際誌
Tongzheng Xin, Yuhong Zhao, Reza Mahjoub, Jiaxi Jiang, Apurv Yadav, Keita Nomoto, Ranming Niu, Song Tang, Fan Ji, Zakaria Quadir, David Miskovic, John Daniels, Wanqiang Xu, Xiaozhou Liao, Long-Qing Chen, Koji Hagihara, Xiaoyan Li, Simon Ringer, Michael Ferry
Science Advances 7 ( 23 ) eabf3039 - eabf3039 2021年06月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：American Association for the Advancement of Science (AAAS)
Strengthening of magnesium (Mg) is known to occur through dislocation accumulation, grain refinement, deformation twinning, and texture control or dislocation pinning by solute atoms or nano-sized precipitates. These modes generate yield strengths comparable to other engineering alloys such as certain grades of aluminum but below that of high-strength aluminum and titanium alloys and steels. Here, we report a spinodal strengthened ultralightweight Mg alloy with specific yield strengths surpassing almost every other engineering alloy. We provide compelling morphological, chemical, structural, and thermodynamic evidence for the spinodal decomposition and show that the lattice mismatch at the diffuse transition region between the spinodal zones and matrix is the dominating factor for enhancing yield strength in this class of alloy.
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Stability of crystallographic texture in laser powder bed fusion: Understanding the competition of crystal growth using a single crystalline seed 査読あり 国際誌
Takuya Ishimoto, Koji Hagihara, Kenta Hisamoto, Takayoshi Nakano
Additive Manufacturing 43 102004 - 102004 2021年05月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
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Formation of <0001>-rotation-type kink boundary in Mg–Zn–Y alloy with long-period stacking ordered structure 査読あり 国際誌
Michiaki Yamasaki, Tsuyoshi Mayama, Tsubasa Matsumoto, Koji Hagihara, Daria Drozdenko, Yoshihito Kawamura
Materials Science and Engineering: A 819 141466 - 141466 2021年05月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
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Surprising increase in yield stress of Mg single crystal using long-period stacking ordered nanoplates 査読あり 国際誌
Koji Hagihara, Ryohei Ueyama, Michiaki Yamasaki, Yoshihito Kawamura, Takayoshi Nakano
Acta Materialia 209 - 116797 2021年04月
担当区分：筆頭著者 記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
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Kink-band formation in directionally solidified Mg/Mg2Yb and Mg/Mg2Ca eutectic alloys with Mg/Laves-phase lamellar microstructure 査読あり 国際誌
Koji Hagihara, Kosuke Miyoshi
Journal of Magnesium and Alloys in press 2021年04月
担当区分：筆頭著者 記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
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Orientation dependence of the wear resistance in the Co–Cr–Mo single crystal 査読あり 国際共著 国際誌
Takayoshi Nakano, Koji Hagihara, Ana R. Ribeiro, Yusuke Fujii, Tsubasa Todo, Ryo Fukushima, Luís Augusto Rocha
Wear 478-479 203758 2021年03月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
This is the report clarifying the orientation dependence of the wear behavior of Co–Cr–Mo alloy. The wear resistance of the Co–Cr–Mo alloy with face-centered cubic (fcc) structure was found to be higher on the planes in order of {110}, {001} and {111}. Quantitatively, the wear resistance on {110} is 1.5 times larger than that on {111}. The tendency showed in coincident with the orientation dependence of the surface hardness, as empirically suggested. However, we additionally found in the observation of the worn surface in the fcc-single crystals that the volume fraction of the hexagonal close-packed (hcp)-phase, which was formed as the strain-induced martensite during the wear test, was larger in the same order of the wear resistance. The variation in formation frequency of the hcp-phase during the wear test can be explained by focusing on the Schmid factor along the resultant direction of the applied stress and the friction stress. On the {111} surface where the Schmid factor for the strain-induced ε-martensite formation is small, homogeneous deformation microstructure covered by it was not developed even after long-time wear, resulting in lower wear resistance. The results strongly suggest that not only the hardness, but the distribution of the ε-martensite is important to control the wear behavior of the Co–Cr alloys with the extremely low stacking fault energy, and it can be achieved by the crystal orientation control in the γ-phase.
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Inducement of kink-band formation in directionally solidified Mg/Mg17Al12 eutectic alloy - Inspired by the deformation behavior of the long-period stacking ordered (LPSO) phase 査読あり 国際誌
K. Hagihara, K. Hayakawa, K. Miyoshi
Materials Science & Engineering A 798 140087 2020年09月
担当区分：筆頭著者 記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
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Morphology and mechanical properties of the T-Al6Mg11Zn11 phase in the eutectic microstructure of Al–Zn–Mg ternary alloys 査読あり 国際誌
N. Takata, T. Okano, M. Aikawa, A.Suzuki, M. Kobashi, K. Hagihara
Intermetallics 124 106881 2020年07月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
-
Kink formation process in long-period stacking ordered Mg-Zn-Y alloy 査読あり 国際誌
S. Yamasaki, T. Tokuzumi, W. Li, M. Mitsuhara, H. Nakashima, K. Hagihara, T. Fujii
Acta Materialia 195 25 - 34 2020年06月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier BV
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Loading orientation dependence of the formation behavior of deformation kink bands in the Mg-based long-period stacking ordered (LPSO) phase 査読あり 国際誌
Koji Hagihara, Takuya Okamoto, Ryohei Ueyama, Michiaki Yamasaki, Yoshihito Kawamura, Takayoshi Nakano
Materials Transactions 61 ( 5 ) 1821 - 1827 2020年01月
担当区分：筆頭著者 記述言語：英語 掲載種別：研究論文（学術雑誌）
© 2019 The Japan Institute of Metals and Materials The variation in the deformation behavior of a directionally solidified (DS) Mg-based long-period stacking ordered (LPSO)-phase crystal depending on the loading orientation was examined. The frequency of formation of the beak-like shape of the deformation band, which is known as one of the important deformation mechanisms in the LPSO phase, monotonically decreased as the inclination angle of the loading orientation with respect to the crystal growth direction in the DS crystal increased, and was accompanied by a decrease in the yield stress due to the activation of basal slip. Deformation bands formed along a direction approximately perpendicular to the grain boundary independent of the loading orientation. The crystal rotation axes selected in the deformation bands were perpendicular to [0001] in almost all grains, independent of the loading orientation. However, the rotation axes in the bands were not fixed but varied between h1010 - i and h1120 - i; this variation was correlated with the loading axis. These observed features strongly suggest that the deformation bands formed in the LPSO phase are predominantly deformation kink bands and that the formation mechanism itself does not vary with the loading orientation but instead its details. The selectivity of the crystal rotation axis in the kink band is strongly affected by the loading orientation.
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Control of crystallographic orientation by metal additive manufacturing process of β-type Ti alloys based on the bone tissue anisotropy 招待あり 査読あり 国際誌
Takayoshi Nakano, Takuya Ishimoto, Aira Matsugaki, Koji Hagihara, Yuichiro Koizumi, Ryosuke Ozasa
MATEC Web of Conferences 321 05002 - 05002 2020年
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：EDP Sciences
Variation in the scanning strategy for β-type Ti alloys during additive manufacturing (AM) enables the fabrication of a singlecrystal-like microstructure possessing a crystallographic texture, in which the low-Young’s modulus-<100> direction is aligned along a specific direction. Thus, metal biomaterial with low elasticity, comparable to the bone Young’s modulus, can be developed by AM, which will contribute to suppress the stress shielding of bone and prevent degradation of bone tissue anisotropy.
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Enhancement of plastic anisotropy and drastic increase in yield stress of Mg-Li single crystals by Al-addition followed by quenching 査読あり
K. Hagihara, K. Mori, T. Nakano
Scripta Materialia 2019年07月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Quantitative ultrasound (QUS) axial transmission method reflects anisotropy in micro-arrangement of apatite crystallites in human long bones: A study with 3-MHz-frequency ultrasound 査読あり
T. Ishimoto, R. Suetoshi, D. Cretin, K. Hagihara, J. Hashimoto, A. Kobayashi, T. Nakano
Bone 127 82 - 90 2019年07月
掲載種別：研究論文（学術雑誌）
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Fabrication of the beta-titanium alloy rods from a mixture of pure?metallic element powders via selected laser melting 査読あり
M. Todai, T. Nagase, T. Hori, H. Motoki, S.-H. Sun, K. Hagihara, T. Nakano
Materials Science Forum 941 1260 - 1263 2019年07月
掲載種別：研究論文（学術雑誌）
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Strengthening of Mg-based long-period stacking ordered (LPSO) phase with deformation kink bands 査読あり
K. Hagihara, M. Yamasaki, Y. Kawamura, T. Nakano
Materials Science & Engineering A 763 138163 2019年07月
掲載種別：研究論文（学術雑誌）
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Additive Manufacturing プロセスによるシリサイド金属間化合物の結晶方位・組織制御 査読あり 国際誌
萩原幸司, 石本卓也, 孫世海, 中野貴由
スマートプロセス学会誌 8 84 - 89 2019年04月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Cr, Ir 共添加によるC40/C11b超高温耐熱複相シリサイドの格子ラメラ組織制御 査読あり
萩原幸司, 池西貴昭, 中野貴由
日本金属学会誌まてりあ 58 81 2019年02月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Mg 基LPSO 相をはじめとする種々の異方性材料に見られる特異な変形帯形成 査読あり
萩原幸司, 中野貴由, 山崎倫昭, 河村能人
日本金属学会誌まてりあ 57 607 2018年11月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Strengthening mechanisms acting in extruded Mg-based long-period stacking ordered (LPSO)-phase alloys 査読あり
K. Hagihara, Z.Li, M. Yamasaki, Y. Kawamura, T. Nakano
Acta Materialia 15 226 - 239 2018年10月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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In-plane positional correlations among dopants in 10H type long period stacking ordered Mg75Zn10Y15 alloy studied by X-ray fluorescence holography 査読あり
T. Nishioka, Y. Yamamoto, K. Kimura, K. Hagihara, H. Izuno, N. Happo, S. Hosokawa, E. Abe, M. Suzuki, T. Matsushita, K. Hayashi
Materialia 3 256 - 259 2018年09月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Plastic deformation behavior and operative slip systems in Mg17Al12 single crystals 査読あり
K. Hagihara, K. Hayakawa
Materials Science & Engineering A 737 393 - 400 2018年09月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Excellent mechanical and corrosion properties of austenitic stainless steel with a unique crystallographic lamellar microstructure via selective laser melting 査読あり
S.-H. Sun, T. Ishimoto, K. Hagihara, Y. Tsutsumi, T. Hanawa, T. Nakano
Scripta Materialia 159 89 - 93 2018年09月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Configuration of dislocations in low-angle kink boundaries formed in a single crystalline long-period stacking ordered Mg-Zn-Y alloy 査読あり
Tsubasa Matsumoto, Michiaki Yamasaki, Koji Hagihara, Yoshihito Kawamura
Acta Materialia 151 112 - 124 2018年06月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Acta Materialia Inc
The dislocation configuration around low-angle kink boundaries formed in bent single crystalline long-period stacking ordered (LPSO) Mg85Zn6Y9 alloys was investigated. Intragranular misorientation axis (IGMA) analysis through SEM/EBSD observation and g•b analysis through TEM observation were conducted. Various kink bands possessing different lattice rotation axes ranging from <
11¯00>
to <
12¯10>
i.e. along <
11¯00>
<
uvt0>
and <
12¯10>
were revealed using IGMA analysis. TEM observation with g•b analysis unveiled that the <
11¯00>
-rotation kink boundary observed using IGMA analysis consisted of basal <
a>
edge dislocations with one Burgers vector, while the <
12¯10>
/<
uvt0>
-rotation kink boundaries were comprised of basal <
a>
edge dislocations with more than one Burgers vector. Low-angle kink boundaries were regarded as low-angle tilt boundaries consisting of perfect basal <
a>
dislocations, regardless of their rotation axes. The formation of various kink bands with <
uvt0>
-combination-rotation axes ranging from <
11¯00>
to <
12¯10>
suggests that the statistically stored basal <
a>
dislocations may turn into geometrically necessary basal <
a>
edge dislocations during the initial stage of low-angle kink boundary formation. When a kink boundary is considered as a disclination, IGMA analysis capable of determining the lattice rotation axis and the angle is effective in evaluating the Frank vector of the kink boundary. -
C40/C11b超高温耐熱複相シリサイド合金における特異な「cross-lamellar microstructure」の発達 招待あり
萩原幸司, 池西貴昭, 中野貴由
日本金属学会誌まてりあ 57 204 2018年05月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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金属積層造形法における形状・組織制御による異方性付与 招待あり
萩原幸司, 石本卓也, 中野貴由
日本金属学会誌まてりあ 57 145 - 149 2018年04月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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チタン単結晶の塑性変形機構 招待あり 査読あり
萩原幸司
軽金属 68 172 - 180 2018年04月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Strain-rate dependence of deformation behavior of LPSO-phases 査読あり
Koji Hagihara, Zixuan Li, Michiaki Yamasaki, Yoshihito Kawamura, Takayoshi Nakano
Materials Letters 214 119 - 122 2018年03月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier B.V.
This is the first report clarifying the influence of the strain rate on the deformation behavior of Mg-based long-period stacking ordered (LPSO) phases with 14H, 18R, and 10H structures. The flow stress by basal slip showed a weakly positive or negligible strain-rate dependence, while the flow stress accompanied by the formation of deformation kink bands showed a unique negative strain-rate dependence. These results give the first experimental evidence on the recent proposal that Zn and Y atoms segregate at the kink band boundaries and hinder their migration, from the viewpoint of the mechanical properties.
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Phonon excitations in a single crystal Mg<inf>85</inf>Zn<inf>6</inf>Y<inf>9</inf> with a synchronized long-period stacking ordered phase 査読あり
Shinya Hosokawa, Koji Kimura, Jens Rüdiger Stellhorn, Koji Yoshida, Koji Hagihara, Hitoshi Izuno, Michiaki Yamasaki, Yoshihito Kawamura, Yoji Mine, Kazuki Takashima, Hiroshi Uchiyama, Satoshi Tsutsui, Akihide Koura, Fuyuki Shimojo
Acta Materialia 146 273 - 279 2018年03月
記述言語：英語 掲載種別：研究論文（学術雑誌）
© 2018 Acta Materialia Inc. Inelastic X-ray scattering (IXS) experiments were carried out at room temperature at BL35XU of the SPring-8 on a single crystal Mg85Zn6Y9 alloy with a synchronized long-period stacking ordered (LPSO) phase of purely 18R type. The IXS measurements were carried out in both the longitudinal and transverse directions along the Γ-K and Γ-M (momentum vector q⊥ lattice axis c), and Γ-A (q∥c) directions for the energy transfers ω below 40 meV. Peaks arising from longitudinal and transverse acoustic (LA and TA) modes were clearly observed in the IXS spectra. The dispersion relations of the LA and TA modes in the Mg85Zn6Y9 LPSO alloy are mostly similar to those of previous INS data on single crystal pure Mg. New impurity-derived dispersion-less excitation modes are observed along all of the crystal directions at about 5, 10, and 17 meV. Partial vibrational density of states (vDOS) was obtained using an ab initio molecular dynamics simulation, and it was found that the ∼10 meV peak mainly originates from the phonon excitations inside the L12-type Zn6Y8 clusters and the ∼17 meV peak from those between the cluster and the host Mg atoms, and a small shoulder at 5 meV consists of motions of all the elements. These findings clarify that the dispersion-less modes mainly correspond to localized stretching and twisting modes around the impurity clusters in the LPSO alloys.
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Effect of scanning strategy on texture formation in Ni-25 at.%Mo alloys fabricated by selective laser melting 査読あり
Shi-Hai Sun, Koji Hagihara, Takayoshi Nakano
Materials and Design 140 307 - 316 2018年02月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier Ltd
Variations in the crystallographic texture in Ni-25 at.%Mo alloys fabricated by selective laser melting with different scanning strategies were designed for the first time. Single-crystalline-like texture with a short-range order of Mo atoms can be produced via bidirectional scanning along one axis (X-scan) and bidirectional scanning with a 90° rotation in each layer (XY-scan), while only fiber texture was formed in bidirectional scanning with a 67° rotation (Rot-scan). The aligned crystal orientation along the build direction can be varied by the scanning strategy
〈001〉 is preferred in the XY- and Rot-scan samples, while 〈101〉 is preferred in the X-scan sample. The controlling mechanisms of the texture, focusing on the preferential growth directions of the columnar cells and the following epitaxial growth, are discussed. -
Plastic deformation mechanisms of biomedical Co-Cr-Mo alloy single crystals with hexagonal close-packed structure 査読あり
Wataru Kaita, Koji Hagihara, Luis Augusto Rocha, Takayoshi Nakano
SCRIPTA MATERIALIA 142 111 - 115 2018年01月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
This is the first report of the successful fabrication of Co-Cr-Mo biomedical alloy single crystals with a hexagonal close-packed (hcp) structure and the resultant clarification of its deformation behavior. The (0001) < 11 (2) over bar0 > basal and {1 (1) over bar 00} < 11 (2) over bar0 > prismatic slip systems were found to be predominately operative. The critical resolved shear stresses for the basal and prismatic slip systems at ambient temperature are similar to 204 and similar to 272 MPa, respectively, which are much higher than similar to 54 MPa for {111} < 11 (2) over bar > slip in the face-centered cubic (fcc) Co-Cr-Mo phase, quantitatively demonstrating that the hcp phase acts as an effective strengthening phase. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd.
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Mg基LPSO合金に働く強化機構
萩原 幸司, 山崎 倫昭, 河村 能人, 中野 貴由
M&M材料力学カンファレンス 2018 ( 0 ) 2018年
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：一般社団法人 日本機械学会
<p>Plastic deformation behavior of extruded alloy mainly composed of long-period stacking ordered phase (LPSO-phase) was examined by compression test, as a function of extrusion ratio, temperature and loading orientation. The yield stress showed a strong loading orientation dependence and the values were much higher along the extrusion direction (0°-orientation) than those along the direction inclined 45° with respect to the extrusion direction (45°-orientation), irrespective of the extrusion ratio. In the deformation along the 45°-orientation the basal slip predominantly occurred in all the specimens. In the deformation along the 0°-orientation, on the other hand, formation of deformation kink band was accompanied in addition to the basal slip, and its formation frequency was different depending on the extrusion ratio. The influence of the variation in texture as a function of extrusion ratio, and in addition the influence of kink deformation bands introduced in the alloy during the extrusion process to the plastic deformation behavior and mechanical properties are quantitatively discussed.</p>
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Experimental clarification of the cyclic deformation mechanisms of β-type Ti?Nb?Ta?Zr-alloy single crystals developed for the single-crystalline implant 査読あり
K. Hagihara, T. Nakano
International Journal of Plasticity 98 27 - 44 2017年11月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
1400℃でも使用可能な超高温耐熱材料を開発 国際誌
萩原幸司, 中野貴由
Ceramics Japan 52 724 2017年09月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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「高機能性構造材料」としてのマグネシウム合金開発 査読あり
萩原幸司
軽金属 67 293 - 300 2017年08月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
DOI： 10.2464/jilm.67.293
-
Unusual dynamic precipitation softening induced by dislocation glide in biomedical beta-titanium alloys 査読あり
K. Hagihara, T. Nakano, M. Todai
Scientific Reports 7 8056 2017年07月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
粉末積層造形法による形状と組織制御による異方性付与 査読あり
中野貴由, 石本卓也, 萩原幸司
粉体および粉末冶金 64 ( 6 ) 259 - 264 2017年06月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
DOI： 10.2497/jjspm.64.259
-
Outstanding compressive creep strength in Cr/Ir-codoped (Mo0.85Nb0.15)Si2 crystals with the unique cross-lamellar microstructure 査読あり
K. Hagihara, T. Ikenishi, H. Araki, T. Nakano
Scientific Reports 7 3936 2017年05月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
Texture control of beta-type Ti?15Zr?5Mo?3Al alloy by selective laser melting for the development of novel implants with an extremely low Young’s modulus 査読あり
T. Ishimoto, K. Hagihara, K. Hisamoto, S.-H.Sun, T. Nakano
Scripta Materialia 132 34 - 38 2017年04月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
Development of unique cross-lamellar microstructure, resulting in the drastic increase in fracture toughness in Cr/Ir-codoped (Mo0.85Nb0.15)Si-2 crystals 査読あり
Koji Hagihara, Takaaki Ikenishi, Takayoshi Nakano
SCRIPTA MATERIALIA 131 19 - 23 2017年04月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
We first found a development of unique "cross-lamellar microstructure" in the (Mo0,85Nb0,15)Si-2 C40/C11(b) two-phase crystals which is a promising ultrahigh-temperature structural material, via the codoping of Cr and Ir. In the cross-lamellar microstructure, rod-like C11(b)-phase grains that extend along a direction perpendicular to the lamellar interface develop in addition to fine lamellae. The fine lamellar microstructure increases in the frequency of delamination for crack-tip blunting, and in addition the rod-like C11(b)-phase grains enhances its effectiveness by inducing the shear-ligament-like toughening. As a result, the drastic increase in fracture toughness, which was never accomplished until now, could be first achieved. (C) 2016 Acta Materialia Inc Published by Elsevier Ltd. All rights reserved.
-
In-Plane Positional Fluctuations of Zinc Atoms in Single Crystal Mg85Zn6Y9 Alloy Studied by X-ray Fluorescence Holography 査読あり
K. Kimura, K. Hayashi, K. Hagihara, H. Izuno, N. Happo, S. Hosokawa, M. Suzuki, H. Tajiri
Materials Transactions 58 539 - 542 2017年03月
記述言語：英語 掲載種別：研究論文（学術雑誌）
-
Successful additive manufacturing of MoSi2 including crystallographic texture and shape control 査読あり
Koji Hagihara, Takayoshi Nakano, Masahiro Suzuki, Takuya Ishimoto, Suyalatu, Shi-Hai Sun
JOURNAL OF ALLOYS AND COMPOUNDS 696 ( 696 ) 67 - 72 2017年03月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCIENCE SA
MoSi2 is one of the promising candidates for ultrahigh-temperature structural materials. However, its product fabrication has been limited owing to its significant brittleness until now. As an approach to overcome this, we have first successfully fabricated MoSi2 samples via additive manufacturing (AM). Control of the thermal expansion coefficient of the start plate for AM is important for building a three-dimensional MoSi2 product with a low deformability. Moreover, unidirectional laser scanning is found to be significantly effective for controlling the crystallographic texture in MoSi2 with a low crystal symmetry. By the unidirectional scanning, [001] texture could be developed along the scanning direction, which possibly results in the fabrication of the MoSi2 products with better high-temperature strength. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license.
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Effect of building direction on the microstructure and tensile properties of Ti-48Al-2Cr-2Nb alloy additively manufactured by electron beam melting 査読あり
Mitsuharu Todai, Takayoshi Nakano, Tianqi Liu, Hiroyuki Y. Yasuda, Koji Hagihara, Ken Cho, Minoru Ueda, Masao Takeyama
Additive Manufacturing 13 61 - 70 2017年01月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Elsevier B.V.
This paper clarified a novel strategy to improve the tensile properties of the Ti-48Al-2Cr-2Nb alloys fabricated by electron beam melting (EBM), via the finding of the development of unique layered microstructure composed of duplex-like fine grains layers and coarser γ grains layers. It was clarified that the mechanical properties of the alloy fabricated by EBM can be controlled by varying an angle θ between EBM-building directions and stress loading direction. At room temperature, the yield strength exhibits high values more than 550 MPa at all the loading orientations investigated (θ = 0, 45 and 90�). In addition, the elongation at θ = 45� was surprisingly larger than 2%, owing to the development of this unique layered microstructure. The anisotropy of the yield strength decreased with increasing temperature. All the examined alloys exhibited a brittle-ductile transition temperature of approximately 750 �C and the yield strength and tensile elongation at 800 �C were over 350 MPa and 40%, respectively. By the detailed observation of the microstructure, the formation mechanism of the unique layered microstructure was found to be closely related to the repeated local heat treatment effect during the EBM process, and thus its control is further possible by the tuning-up of the process parameters. The results demonstrate that the EBM process enables not only the fabrication of TiAl products with complex shape but also the control of the tensile properties associated with the peculiar microstructure formed during the process.
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Anomalous strengthening behavior of Co-Cr-Mo alloy single crystals for biomedical applications 査読あり
Koji Hagihara, Takayoshi Nakano, Keita Sasaki
SCRIPTA MATERIALIA 123 149 - 153 2016年10月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
This is the first repot on the deformation behavior of Co-Cr-Mo biomedical alloy single crystals predominantly having an fcc structure. In the single crystal, one of four epsilon-variants was selectively formed, and its geometry was found to drastically affect the mechanical properties. The yield stress in the 1111] orientation, in which the formation of epsilon-phase strain-induced martensite (SIM) crosses the grown-in epsilon-variant, was more than six times larger than that in the [149] orientation, where SIM was formed parallel to the grown-in s-variant. The intersection mechanism of the epsilon-variants is discussed via observations of the deformation microstructure. (C) 2016 Elsevier B.V. All rights reserved.
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Plastic deformation behavior of the Mg-based LPSO phases with various crystal structures 査読あり
K. Hagihara, T. Okamoto, H. Izuno, M. Yamasaki, M. Matsushita, T. Nakano, Y. Kawamura
Proceedings of PRICM9 27 - 31 2016年08月
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス）
-
Effect of additional elements on fracture toughness of (Mo0.85Nb0.15)Si-2 C40/C11(b) lamellar-structured crystals 査読あり
Koji Hagihara, Koretaka Yuge, Takaaki Ikenishi, Haruka Araki, Takayoshi Nakano
MATERIALS LETTERS 177 99 - 103 2016年08月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCIENCE BV
Variations in the fracture toughness of lamellar-structured C40/C11(b) silicides as a function of the microstructure were examined by using Cr-, Zr-, and Ir-added (Mo0.85Nb0.15)Si-2 crystals. Fracture toughness variation showed strong orientation dependence, governed by the occurrence frequency of delamination and crack deflection. The refinement of the lamellar microstructure by Ir-addition led to an increase in fracture toughness when the lamella boundary was laid perpendicular to the loading axis, although it decreased at other orientations. The variation in fracture toughness when the alloyed crystal was loaded parallel to the lamellar boundary qualitatively showed good agreement with the predictions by first principles calculations on the cohesive energy of the C40/C11(b) interface. (C) 2016 Elsevier B.V. All rights reserved.
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Crystal-orientation-dependent corrosion behaviour of single crystals of a pure Mg and Mg-Al and Mg-Cu solid solutions 査読あり
Koji Hagihara, Masayoshi Okubo, Michiaki Yamasaki, Takayoshi Nakano
CORROSION SCIENCE 109 68 - 85 2016年08月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
Mg alloys are promising candidates for biodegradable materials. To control their dissolution rate, the orientation-dependent corrosion behaviour of pure-Mg single crystals was examined. The corrosion rates increased in the order (0001) < (11<(2)over bar>0) < (10<(1)over bar>0) < (11<(2)over bar>3) < (10<(1)over bar>2). We found the anodic reaction governs the orientation-dependent corrosion behaviour. The charge-transfer and film resistances were strongly orientation-dependent. Effects of Al or Cu-addition to the orientation-dependent corrosion behaviour were also examined as model materials. Al-addition promoted passivation in anodic polarization, while Cu-addition activated the cathodic reaction. However, neither Al nor Cu influenced the order of orientation-dependent corrosion behaviour. Such orientation-dependence may originate from the variation in surface atomic-packing density. (C) 2016 Elsevier Ltd. All rights reserved.
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Isotropic plasticity of β-type Ti-29Nb-13Ta-4.6Zr alloy single crystals for the development of single crystalline β-Ti implants 査読あり
K. Hagihara, T. Nakano, H. Maki, Y. Umakoshi, M. Niinomi
Scientific Report 6 20779 2016年07月
記述言語：英語 掲載種別：研究論文（学術雑誌）
DOI： 10.1038/srep29779
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シンクロ型LPSO構造の力学的性質とキンク変形挙動 査読あり
萩原幸司, 森川龍哉, 東田賢二
金属 （雑誌） 86 472 - 479 2016年06月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Plastic deformation behavior of 10H-type synchronized LPSO phase in a Mg-Zn-Y system 査読あり
Koji Hagihara, Takuya Okamoto, Hitoshi Izuno, Michiaki Yamasaki, Masafumi Matsushita, Takayoshi Nakano, Yoshihito Kawamura
ACTA MATERIALIA 109 90 - 102 2016年05月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
We recently succeeded in fabricating a new type of synchronized long-period stacking ordered (LPSO) phase crystal with the 10H crystal structure in the Mg-Zn-Y system. In the 10H LPSO phase, the long-range order of the Zn/Y-enriched L1(2)-like cluster was more significantly developed than that in the previously reported 18R LPSO phases in the Zn/Y concentrated layer. As the operative deformation mode in the 10H phase, (0001)<11<(2)over bar>0> basal slip was found to predominate. In addition, the formation of deformation kink bands was confirmed under conditions in which the operation of basal slip was macroscopically hindered. These features were similar to those observed in the 18R phase, but some differences were also observed in the deformation behavior owing to the development of in-plane ordering in the Zn/Y concentrated layers. The formation of a deformation kink band was localized in the deformation of the 10H crystal, and the localization of the kink-band formation was more enhanced in a specimen annealed at 500 degrees C for 24 h, in which the long-range order of the L1(2)-like cluster was pronounced. In addition, the operation of nonbasal slip was hindered in 10H crystals during deformation at high temperatures. The localization of kink-band formation and the prohibition of nonbasal slip induced the frequent formation of microcracks during the deformation of the 10H crystal, which led to fracture in the early stage of deformation. Experimental results demonstrated that the development of in-plane ordering of the L1(2)-like cluster in the Zn/Y concentrated layer is significantly detrimental to the ductility of the synchronized LPSO phase. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Electron backscatter diffraction pattern analysis of the deformation band formed in the Mg-based long-period stacking ordered phase 査読あり
Koji Hagihara, Takuya Okamoto, Michiaki Yamasaki, Yoshihito Kawamura, Takayoshi Nakano
SCRIPTA MATERIALIA 117 32 - 36 2016年05月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
A newly proposed analysis protocol using electron backscatter diffraction pattern analysis in scanning electron microscopy (SEM-EBSD) clarified that the deformation bands formed in the Mg-based long-period stacking ordered (LPSO) phase are predominantly deformation kink bands. The kink band contains many additional boundaries within it, and the coalescence of these boundaries varies the crystal rotation angle and rotation axis at the kink band boundaries during their development. The reason for the appearance of a "beak-like" shape in deformation kink band in the LPSO phase was clarified by proposing a unique three-dimensional morphology. (C) 2016 Elsevier Ltd. All rights reserved.
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High-temperature deformation behavior of (Mo0.85Nb0.15)Si2 crystals with C40/C11b lamellar microstructure 査読あり
K. Hagihara, H. Araki, T. Ikenishi, T. Nakano
Materials Science Forum 879 677 - 683 2016年04月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Creep-deformation behavior of (Mo0.85Nb0.15)Si-2 lamellar-structured C40/C11(b) two-phase crystals 査読あり
Koji Hagihara, Haruka Araki, Takaaki Ikenishi, Takayoshi Nakano
ACTA MATERIALIA 107 196 - 212 2016年04月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
The creep-deformation behavior of (Mo0.85Nb0.15)Si-2 crystals that were composed of C40 and C11(b) two-phases with an oriented lamellar microstructure was examined over 1200-1400 degrees C under compression. The creep behavior of the crystals varied greatly depending on the orientation of the loading axis with respect to the lamellar interfaces. The steady-state creep strain rate (SSCR) when the loading orientation was parallel to the lamellar interfaces (0 degrees-orientation) was approximately 2 orders of magnitude lower than that when the loading orientation was inclined by 45 degrees (45 degrees-orientation). Creep tests were performed also with single crystals of C40-single-phase (Mo0.85Nb0.15)Si-2, and proved that the C40-phase effectively acts as a strengthening phase in the creep behavior of the C40/C11(b) duplex-phase crystals. The variant-1-type C11(b) phase grains, which have a loading orientation parallel to [001], were also found to act as an effective strengthening component. The SSCR of the 0 degrees-orientation was succeeded to be further decreased by controlling the lamellar microstructure via the addition of Cr. The SSCR of the 1 at%-Cr-added lamellar-structured crystal under 300 MPa in the 0 degrees-orientation was approximately a third of that of the non-added ternary crystal. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Microstructure and fracture toughness in boron added NbSi2(C40)/MoSi2(C11(b)) duplex crystals 査読あり
Mitsuharu Todai, Koji Hagihara, Kyosuke Kishida, Haruyuki Inui, Takayoshi Nakano
SCRIPTA MATERIALIA 113 236 - 240 2016年03月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
The effect of B-addition on the microstructure and fracture toughness of (Mo0.85Nb0.15)Si-2 crystals with an oriented lamellar microstructure was investigated. B-addition led to an increase in the volume fraction of the Cub phase, which possesses different orientation relationship from that of the fine lamellae, and a reduction in their precipitation rate. The fracture toughness of the B-added crystal with the varied microstructure exhibited a value more than 4.0 MPa m(1/2), that was significantly higher than that of the ternary crystal. (C) 2015 Elsevier Ltd. All rights reserved.
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Orientation dependence of the deformation kink band formation behavior in Zn single crystal 査読あり
Koji Hagihara, Tsuyoshi Mayama, Masahito Honnami, Michiaki Yamasaki, Hitoshi Izuno, Takuya Okamoto, Tetsuya Ohashi, Takayoshi Nakano, Yoshihito Kawamura
INTERNATIONAL JOURNAL OF PLASTICITY 77 174 - 191 2016年02月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
Variations in deformation kink band formation behavior with loading orientation were examined by the combination of experiment and computer simulation, using the Zn single crystal as a model material. Based on the results, the controlling factors for the formation behavior of deformation kink bands and its general features were discussed. Due to compression parallel to the basal plane, several deformation bands formed in the Zn single crystal. By the examination of the crystallographic nature of the deformation bands, they were found to exhibit three characteristic features: an ambiguous crystal rotation axis on the [00011 zone axis, an arbitrary rotation angle with a wide variation, and a variation in the crystal rotation angle within the deformation band boundary itself. In addition, an analysis protocol to classify the nature of the deformation bands via the observation on (0001) was newly proposed. As a result, the deformation bands formed in the Zn single crystal were confirmed to be predominantly deformation kink bands rather than deformation twining.
Among the abovementioned three crystallographic features, we first experimentally confirmed by using the single crystal that the variations in the rotation axis in deformation kink bands exhibit a strong dependence on loading orientation. Using computer simulation based on the crystal plasticity finite element analysis, the origin of the variation in rotation axis in deformation kink bands was clarified to be due to the initiation of different types of basal dislocations that construct the deformation kink band boundaries, which depends on the loading orientation. In addition, the variations in types of the dislocations owing to the internal stress were found to cause the significant waviness of the deformation band boundaries on (0001) specimen surface. (C) 2015 Elsevier Ltd. All rights reserved. -
Elastic-modulus enhancement during room-temperature aging and its suppression in metastable Ti-Nb-Based alloys with low body-centered cubic phase stability 査読あり
M. Tane, K. Hagihara, M. Ueda, T. Nakano, Y. Okuda
ACTA MATERIALIA 102 373 - 384 2016年01月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
Changes in the elastic properties during room-temperature aging (RT aging) of metastable Ti-Nb-based alloy single crystals with low body-centered cubic (bcc)-phase stability were investigated. The elastic stiffness components of Ti-Nb-Ta-Zr alloys with different Nb concentrations were measured by resonant ultrasound spectroscopy during RT aging; the results revealed that shear moduli c' and c(44) were increased by RT aging. In the alloy with the lowest Nb concentration, i.e., with the lowest bcc phase stability, shear moduli c' and c44 were enhanced by the largest amount. The increase rates were similar to 5% for 1.1 x 10(7) s (127 days), whereas the bulk modulus was hardly changed by aging. In Ti-Nb-Ta-Zr-O alloys with different oxygen concentrations, shear moduli cl and c44 of the alloy with the lowest oxygen concentration increased most significantly. Moreover, the electrical resistivity of Ti-Nb-Ta-Zr and Ti-Nb-Ta-Zr-O alloys was increased by RT aging. Importantly, the enhancements of shear moduli and electrical resistivity were suppressed by increases in the bcc-phase stability (i.e., increase in the Nb concentration) and oxygen concentration; these factors are known to suppress omega (hexagonal) phase formation. However, transmission electron microscopy (TEM) observations revealed that only a diffuse or structure-an omega-like lattice distortion-was formed after RT aging. On the basis of alloying element effects, TEM observations, and analysis of the changes in elastic properties by using a micromechanics model, it was deduced that the enhancements of shear moduli and electrical resistivity were possibly caused by the formation of a diffuse omega structure. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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六方晶系材料における変形帯形成に関する，実験，計算両観点からの考察 査読あり
萩原 幸司, 眞山 剛, 山崎 倫昭, 大橋 鉄也, 河村 能人, 中野 貴由
M&M材料力学カンファレンス 2016 ( 0 ) OS01 - 11 2016年
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：一般社団法人 日本機械学会
<p>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, in this study the crystallographic nature of deformation bands formed in the hcp-Zn was first examined in details both by the experimental and computational approaches. And the obtained results were compared to those observed in LPSO phase. As a result, it was found that deformation bands formed in them showed many similar features, such as 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 etc. This suggests that the developing feature of the deformation bands in LPSO phase crystals can be explained by the "deformation kink band formation model".</p>
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生体骨程度の低ヤング率を示す単結晶ボーンプレートの創製
當代 光陽, 萩原 幸司, 中野 貴由
日本バイオマテリアル学会大会予稿集 37回 238 - 238 2015年11月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：日本バイオマテリアル学会
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シンクロ型LPSO構造相の塑性変形挙動 査読あり
萩原幸司, 東田賢二
日本金属学会誌まてりあ 54 60 - 64 2015年10月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Mechanisms of lamellar structure formation and Cr interfacial segregation in C11(b)-MoSi2/C40-NbSi2 dual phase silicide verified by a phase-field simulation incorporating elastic inhomogeneity 査読あり
Toshihiro Yamazaki, Yuichiro Koizumi, Koretaka Yuge, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Kyosuke Kishida, Haruyuki Inui
COMPUTATIONAL MATERIALS SCIENCE 108 358 - 366 2015年10月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCIENCE BV
We developed a phase-field model of C11(b)-MoSi2/C40-NbSi2 duplex silicide incorporating elastic inhomogeneity, and simulated microstructure formation and interface segregation. We examined the effect of elastic inhomogeneity on the morphology, volume fraction of the C11(b)-precipitate, stress distribution, and solute partitioning. In the simulations, parameters evaluated by first-principles calculation are used for the experimentally unknown parameters. The lamellar structure was not formed in the case incorporating the elastic strain energy only and ignoring the anisotropy of the interfacial energy. When the anisotropy of the interfacial energy was taken into account, the lamellar structure was formed parallel to (0001)(C40) as observed in the experiment. It was also found that the elastic strain energy changes the equilibrium concentrations by > 0.2 at%, but the difference between the equilibrium concentrations in homogeneous and inhomogeneous systems was < 0.1 at%. The interfacial segregation was also hardly affected by the elastic inhomogeneity. These results confirm that elastic inhomogeneity can be neglected in the simulation of MoSi2/NbSi2 lamellar silicide. (C) 2015 Elsevier B.V. All rights reserved.
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Effects of stacking sequence and short-range ordering of solute atoms on elastic properties of Mg-Zn-Y alloys with long-period stacking ordered structures 査読あり
M. Tane, H. Kimizuka, K. Hagihara, S. Suzuki, T. Mayama, T. Sekino, Y. Nagai
ACTA MATERIALIA 96 170 - 188 2015年09月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
The effects of stacking sequence and short-range ordering of solute atoms on the elastic properties of Mg-Zn-Y alloy single crystals with an 18R- or 10H-type long-period stacking ordered (LPSO) structure were studied. Instead of single crystals, the growth of which can be quite difficult, two directionally solidified (DS) Mg-Zn-Y alloy polycrystals, mainly consisting of 18R- or 10H-type LPSO structure, were prepared. X-ray pole figure analyses revealed that fiber textures, which differed in the two prepared alloys, were formed in the DS polycrystals. For the DS polycrystals, a complete set of elastic constants was measured during cooling from 300 to 7.5 or 5.5 K. By analyzing the elastic stiffness of DS polycrystals on the basis of a newly developed inverse Voigt-Reuss-Hill approximation, in which the detailed crystallographic texture could be taken into account, the elastic stiffness components of the single-crystalline LPSO phases from 300 to 7.5 or 5.5 K were determined. The elastic properties of the 18R- and 10H-LPSO phases were also evaluated by first-principles calculations based on density functional theory. Comparison of the measured elastic properties at 5.5 or 7.5 K with the first-principles calculations revealed that the elastic properties of the LPSO phase were virtually dominated by the stacking sequence of the LPSO structures and the formation energy of short-range ordered solute atom clusters, formed at the four consecutive atomic stacking layers. Importantly, the effects of the formation energy and stacking sequence were significant in the elastic moduli related to the atomic bonding between the stacking layers. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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シンクロ型LPSO構造相の塑性変形挙動 査読あり
萩原幸司, 東田賢二
まてりあ(日本金属学会誌) 54 60 - 64 2015年02月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Crystallographic nature of deformation bands shown in Zn and Mg-based long-period stacking ordered (LPSO) phase 査読あり
Koji Hagihara, Michiaki Yamasaki, Masahito Honnami, Hitoshi Izuno, Masakazu Tane, Takayoshi Nakano, Yoshihito Kawamura
PHILOSOPHICAL MAGAZINE 95 ( 2 ) 132 - 157 2015年01月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：TAYLOR & FRANCIS LTD
Formation of curious deformation bands has been reported as one of the deformation mechanisms occurring in an 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 results were compared to those of the deformation kink bands formed in hcp-Zn and deformation twins formed in hcp-Mg polycrystals. The deformation bands in the LPSO phase was confirmed not to exhibit a fixed crystal orientation relationship with respect to the matrix, different from the case shown in the deformation twin. Instead, the deformation band in the LPSO phase showed 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 predominantly deformation kink bands.
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β型Ti-15Mo-5Zr-3Al合金単結晶を用いた低ヤング率ボーンプレートの開発 査読あり
當代光陽, 萩原幸司, 石本卓也, 山本憲吾, 中野貴由
鉄と鋼 101 ( 9 ) 501 - 505 2015年
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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In-Situ Observation on the Formation Behavior of the Deformation Kink Bands in Zn Single Crystal and LPSO Phase 査読あり
Koji Hagihara, Masahito Honnami, Ryosuke Matsumoto, Yoshihiro Fukusumi, Hitoshi Izuno, Michiaki Yamasaki, Takuya Okamoto, Takayoshi Nakano, Yoshihito Kawamura
MATERIALS TRANSACTIONS 56 ( 7 ) 943 - 951 2015年
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：JAPAN INST METALS
The deformation microstructure and deformation process of the Mg-based long period stacking ordered (LPSO) phase accompanied by the formation of deformation kink bands were examined through dynamical observations during compression tests, and the features were compared to those in Zn single crystals. In both crystals, the formation of deformation kink bands was confirmed in specimens compressed along the direction parallel to the basal plane. The deformation kink bands formed in the directionally solidified (DS) LPSO phase crystals and the Zn single crystals had similar morphologies. Their formation induced plastic strain almost along the c-axis. However, their formation behaviors showed some different features. In the LPSO phase DS crystal, two different migration behaviors of the deformation kink band boundaries existed. The slower migration process was comparable to that observed in Zn single crystals. However, a migration process more than 105 times faster than the slower process was also monitored. The results imply that two different formation mechanisms of the deformation kink band might exist in the LPSO phase crystal.
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Crystal Plasticity Analysis of Development of Intragranular Misorientations due to Kinking in HCP Single Crystals Subjected to Uniaxial Compressive Loading 査読あり
Tsuyoshi Mayama, Tetsuya Ohashi, Yuichi Tadano, Koji Hagihara
MATERIALS TRANSACTIONS 56 ( 7 ) 963 - 972 2015年
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：JAPAN INST METALS
The mechanism and the effective factors for the development of intragranular misorientations due to kinking is studied by a crystal plasticity finite element method. A single crystal with hexagonal close-packed (HCP) structure in which only basal slip system is activated is used as a model material. To activate basal slip system, the initial crystal orientations are set to be the ones whose basal planes are slightly deviated from the compressive direction. The result shows that basal slip and the development of intragranular misorientations are sometimes localized near the center of the specimen depending on the initial deviation angle, strain hardening rate, and strain rate sensitivity. The mechanism is discussed in terms of the nonuniform stress distribution and lattice rotation. The effect of slight changes in the boundary conditions shows significant effect on the positions of slip localization. In summary, the present numerical results suggest that there are a number of effective factors for the development of the intragranular misorientations due to kinking including initial crystal orientation, material parameters, and boundary conditions.
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イノベーションスタイルの構築に向けた取り組みについて
荒木 秀樹, 中野 貴由, 石本 卓也, 萩原 幸司, 井手 拓哉, 中本 将嗣, 玉岡 秀房
まてりあ 54 ( 10 ) 519 - 521 2015年
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異方性カスタム材質・形状制御について
中野 貴由, 石本 卓也, 萩原 幸司, 井手 拓哉, 中本 将嗣, 蘇亜 拉図, 孫 世海, 荒木 秀樹, 玉岡 秀房
まてりあ 54 ( 10 ) 502 - 504 2015年
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Mechanisms of Cr segregation to C11(b)/C40 lamellar interface in (Mo,Nb)Si-2 duplex silicide: A phase-field study to bridge experimental and first-principles investigations 査読あり
Toshihiro Yamazaki, Yuichiro Koizumi, Koretaka Yuge, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Kyosuke Kishida, Haruyuki Inui
INTERMETALLICS 54 232 - 241 2014年11月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCI LTD
Cr segregation at lamellar interfaces in the MoSi2/NbSi2 duplex silicide was examined using a newly developed phase-field model to elucidate the mechanism of interfacial segregation, which is believed to improve the thermal stability of lamellar structures as well as creep resistance. This is because lamellar structures can improve the high-temperature strength, and the stabilization of the lamellar structures improves creep resistance. The model takes into account the segregation energy determined using first-principles calculations to reflect the chemical interaction between the solute atoms and the interface, in addition to the elastic interaction. Cr segregation occurs at the interface when the segregation energy is considered, whereas no segregation occurs in the case where only the elastic interaction is considered. However, the extent of segregation was much smaller than that observed experimentally when the segregation energy was evaluated using first-principles calculations without considering lattice vibrations (i.e., the calculations were performed for 0 K). A simulation that took into consideration the segregation energy with the lattice vibrations at 1673 K resulted in segregation similar to that observed experimentally, where the Cr-added MoSi2/NbSi2 duplex silicide was equilibrated at 1673 K, namely, the temperature at which the segregation energy was calculated. Thus, it was revealed that the solute-interface chemical interaction and its temperature dependence are responsible for the interfacial segregation of Cr. These results suggest that the segregation energy needs to be taken into account in the search for more effective additive elements for improving the thermal stability of lamellar structures as well as the creep resistance. (C) 2014 Elsevier Ltd. All rights reserved.
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Degradation behavior of Ca-Mg-Zn intermetallic compounds for use as biodegradable implant materials 査読あり
Koji Hagihara, Shuhei Shakudo, Kenta Fujii, Takayoshi Nakano
MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS 44 285 - 292 2014年11月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCIENCE BV
With the goal of developing new biodegradable implant materials, we have investigated the degradation behavior of (Ca, Mg)-based intermetallic compounds. The degradation behavior of the compounds within the Ca-Mg-Zn system was roughly classified into four groups, and their behaviors were strongly influenced by the compositions of the compounds. For example, the Ca3MgxZn((15) (-) x) compound exhibited a large solubility region with varying the Mg/Zn ratio, and the Ca3Mg12Zn3 phase alloy with the lowest Zn content was rapidly broken apart within 6 h of immersion. Alternatively, the Ca3Mg4.6Zn10.4 phase alloy with the highest Zn content retained the bulk shape even after 250 h of immersion. These varying degradation behaviors were ascribed to the difference in the formability of Zn oxide as a protective layer against corrosion on the specimen surfaces, depending on the Zn content. The gained results suggest that there is a feasibility on developing new biodegradable materials based on intermetallic compounds in which the degradation rate can be controlled by their compositions. (C) 2014 Elsevier B.V. All rights reserved.
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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年10月
記述言語：日本語 掲載種別：研究論文（その他学術会議資料等）
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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年10月
記述言語：日本語 掲載種別：研究論文（その他学術会議資料等）
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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年10月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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高機能構造材料開発への取り組み 査読あり
萩原幸司
まてりあ（日本金属学会誌） 53 348 - 354 2014年08月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Control of microstructure and fracture toughness improvement of NbSi2/MoSi2 duplex lamellar silicides by TaC particles dispersion 査読あり
Koji Hagihara, Tatsuya Fushiki, Takayoshi Nakano
SCRIPTA MATERIALIA 82 53 - 56 2014年07月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：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 査読あり
Michiaki Yamasaki, Masafumi Matsushita, Koji Hagihara, Hitoshi Izuno, Eiji Abe, Yoshihito Kawamura
SCRIPTA MATERIALIA 78-79 13 - 16 2014年05月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：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 査読あり
K. Hagihara, Y. Hama, T. Fushiki, K. Yuge, T. Nakano
Materials Science Forum 783-786 1123 - 1128 2014年04月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Ab-initio study of long-period superstructures and anti-phase boundaries in Al-rich γ-TiAl (L10)-based alloys 査読あり
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年04月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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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 査読あり
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年01月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：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 LPSO相の塑性変形にて形成する変形帯の特徴
萩原 幸司, 本浪 雅史, 山崎 倫昭, 岡本 拓也, 伊津野 仁史, 多根 正和, 中野 貴由, 河村 能人
M&M材料力学カンファレンス 2014 ( 0 ) _OS0101 - 1_-_OS0101-2_ 2014年
記述言語：日本語 掲載種別：研究論文（その他学術会議資料等） 出版者・発行元：一般社団法人 日本機械学会
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 査読あり
Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki Inui
Advanced Materials Research 922 832 - 837 2014年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス）
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 招待あり 査読あり 国際誌
Koji Hagihara, Yoichiro Hama, Tatsuya Fushiki, Koretaka Yuge, Takayoshi Nakano
Materials Science Forum 783-786 1123 - 1128 2014年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：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 招待あり
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年11月
記述言語：日本語 掲載種別：研究論文（その他学術会議資料等）
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Cr segregation at C11(b)/C40 interface in MoSi2-based alloys: A first-principles study 査読あり
Koretaka Yuge, Kyosuke Kishida, Haruyuki Inui, Yuichiro Koizumi, Koji Hagihara, Takayoshi Nakano
INTERMETALLICS 42 165 - 169 2013年11月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：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 査読あり
Koji Hagihara, Kenta Fujii, Aira Matsugaki, Takayoshi Nakano
MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS 33 ( 7 ) 4101 - 4111 2013年10月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：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 査読あり
M. Tane, Y. Nagai, H. Kimizuka, K. Hagihara, Y. Kawamura
ACTA MATERIALIA 61 ( 17 ) 6338 - 6351 2013年10月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：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 招待あり
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年09月
記述言語：日本語 掲載種別：研究論文（その他学術会議資料等）
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Deformation behavior of LPSO phase and Zn accompanied by kink band formation 査読あり
K. Hagihara, Y. Fukusumi, M. Yamasaki, R. Matsumoto, M. Honnami, H. Izuno, T. Nakano, Y. Kawamura
Proc. of PRICM8 973 - 978 2013年08月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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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 査読あり
Koji Hagihara, Tetsunori Tanaka, Hitoshi Izuno, Yukichi Umakoshi, Takayoshi Nakano
ACTA MATERIALIA 61 ( 12 ) 4365 - 4373 2013年07月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：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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Misfit strain affecting the lamellar microstructure in NbSi 2/MoSi2 duplex crystals 査読あり
Koji Hagihara, Yoichiro Hama, Koretaka Yuge, Takayoshi Nakano
Acta Materialia 61 ( 9 ) 3432 - 3444 2013年05月
記述言語：英語 掲載種別：研究論文（学術雑誌）
The effect of including an additional element, like Re, Cr, V, Zr or Ir, in (Mo0.85Nb0.15)Si2 crystals, carried out with the aim of improving the thermal stability of the fine lamellar microstructures of the crystals, was examined with the help of first-principles calculations. The addition improved the thermal stability of the microstructures at 1400 °C in all cases, and the effect was especially significant in crystals containing Cr and Zr additives. Quantitative evaluation by Moiré fringe analysis revealed that the misfit strain at the interfaces in crystals with added Cr and Zr was smaller than those in crystals with other elements added. The reduced misfit strain resulted in the suppression of the rapid growth of the C11b phase precipitates that did not possess the variant orientation relationship with the C40 matrix, and hence the thermal stability of the fine lamellar microstructures improved. The results further revealed that the ratio of the atomic size of the additive element to that of Mo, which is the main constituent element in the C11b phase, is an important factor that controlled the misfit strain at the lamellar interface by the result of Cr addition. However, the addition of Zr was found to result in a significant improvement in the thermal stability of the lamellar microstructure, despite the markedly larger atomic radius of Zr compared with that of Mo. This indicates that there may be other factors, in addition to the atomic radius of the additive, contributing to the thermal stability. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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First-principles investigation of phase stability and electronic structure of tetragonal (P4/m) Ga3-xAlxTi2 (x=03) compounds
P. S. Ghosh, A. Arya, U. D. Kulkarni, G. K. Dey, T. Nakano, Y. Umakoshi, K. Hagihara, S. Hata
PHILOSOPHICAL MAGAZINE LETTERS 93 ( 5 ) 273 - 282 2013年05月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：TAYLOR & FRANCIS LTD
We report a first-principles study of the phase stability and electronic structure of tetragonal (P4/m) Ga-3 (x) Al (x) Ti-2 (x=03) compounds to investigate the conspicuous absence of Al3Ti2 in the AlTi phase diagram while isostructural Ga3Ti2 is stable in the GaTi phase diagram. It is found that Ga3Ti2 is the most stable phase compared to its ternary derivatives (Ga-3 (x) Al (x) )Ti-2, with the stability of Al3Ti2 being the lowest. Furthermore, the equimolecular phase mixture of -TiAl and r-Al2Ti is found to be more stable than Al3Ti2. By analysing the total and partial density of states, the valence charge transfer and the valence charge density distributions, we substantiate our conclusions from the perspective of the electronic structure.
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Crystallographic classification of kink bands in an extruded Mg-Zn-Y alloy using intragranular misorientation axis analysis 査読あり
Michiaki Yamasaki, Koji Hagihara, Shin-ichi Inoue, Jason Paul Hadorn, Yoshihito Kawamura
ACTA MATERIALIA 61 ( 6 ) 2065 - 2076 2013年04月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
Within extruded Mg89Zn4Y7 (at.%) alloys containing a long period stacking ordered (LPSO) phase a unique deformation mode referred to as "kink deformation" is found to occur within the LPSO phase grains, forming kink bands that are each represented by an array of geometrically necessary dislocations. Intragranular misorientation axis (IGMA) analysis suggests that this kink deformation results in lattice rotation predominately about the < 1 (1) over bar 0 0 >, < 0 (1) over bar 1 0 >, < 0001 >, and < 1 (2) over bar 1 0 > axes of the 18R-type LPSO structure. IGMA analysis is based on slip-induced lattice rotation and determination of its rotation axis (Taylor axis). Therefore, it is possible to determine the dominant slip mode in a grain that is deformed by matching the Taylor axis for a given slip system to its experimentally obtained IGMA distribution. In this study the strong preference of < 1 (1) over bar 0 0 > and < 0 (1) over bar 1 0 > Taylor axes suggests that kinking occurs through a basal < a > slip mode. The < 0 0 0 1 > Taylor axes suggest that kink bands form through a prismatic < a > slip mode. These axes are categorized as "principal rotation" axes, which result from one Burgers vector of dislocations. Kink bands with a < 1 (2) over bar 1 0 > Taylor axis are produced through combination of basal < a > slip variants. This axis is categorized as a "combination-type rotation" axis, which results from more than one Burgers vector of dislocations. It is concluded that IGMA analysis can be effectively used to study and geometrically classify kink bands. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Yield stress anomaly controlled by the phase stability in NbSi2 single crystals 査読あり
Takayoshi Nakano, Koji Hagihara
SCRIPTA MATERIALIA 68 ( 5 ) 313 - 316 2013年03月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
Effects of alloying elements on the deformation behavior of C40-NbSi2 were examined. Yield stress anomaly (YSA), caused by the formation of a dragging atmosphere around dislocations, was found to be controlled by two factors. Dragging atmospheres were considered to be formed by point defects such as vacancies at 900-1200 degrees C and by substitutional elements at higher temperatures. Variation in YSA depended on the phase stability at higher temperatures. The magnitude of the YSA could be enhanced by increasing the stability of the C11(b)-phase in C40-NbSi2. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Long-period ordered superstructures that appear in an (Al,Ga)-rich (Al,Ga)Ti system 査読あり
Takayoshi Nakano, Koji Hagihara, Satoshi Hata, Hajime Shigyo, Hideharu Nakashima, Yukichi Umakoshi, Ashok Arya, Ulhas D. Kulkarni
Philosophical Magazine 93 ( 1-3 ) 22 - 37 2013年01月
記述言語：英語 掲載種別：研究論文（学術雑誌）
Long-period ordered superstructures in an (Al,Ga)-rich (Al,Ga)Ti system composed of (Al,Ga)x Ti100-x (x = 50-65 at. %) were investigated by using melt-spun ribbons, focusing on the ordering process of the superstructural phases. Compositional regions in which h-(Al,Ga)2Ti (Ga2Zr-type), (Al,Ga)5Ti3 and (Al,Ga) 3Ti2 with threefold, fourfold and fivefold periodicity, respectively, appeared coherently in the L10 matrix were identified by electron diffraction patterns in two different temperature conditions of as-spun (a relatively high-temperature state) and heat-treatment at 700°C (a relatively low-temperature state). The (Al,Ga)5Ti3 superstructural phase always existed between the compositional region where h-(Al,Ga)2Ti and (Al,Ga)3Ti2 dominantly appear. Therefore, periodical ordering proceeds following the periodicity of the concentration wave of pure (Al,Ga) layers parallel to {310) in the Ti (002) layers from threefold to fivefold periodicity via fourfold periodicity. We found that the (Al,Ga)3Ti2 long-period superstructural phase preferentially appeared with increasing Ga concentration in the melt-spun ribbon annealed at 700°C. In other words, the h-(Al,Ga)2Ti superstructure with threefold periodicity preferentially appeared at the high temperature and a low Ga concentration. Thus, the (Al,Ga)3Ti 2-type superstructure was never produced without the addition of Ga in the present study. The long-period ordered superstructures were composed of three pairs of primitive cells, (Al,Ga)Ti2, (Al,Ga)Ti3 and (Al,Ga)Ti4, with periodic atomic arrangements corresponding to lean rhombus, fat rhombus and square, respectively. We discuss the ordering process throughout the (Al,Ga)5 superstructure based on the periodic concentration wave and exchange of atoms. The effect of long-period ordered superstructures on hardness is also mentioned. © 2013 Copyright Taylor and Francis Group, LLC.
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シンクロ型LPSO相の塑性変形挙動 招待あり
萩原 幸司
セミナーテキスト シンクロ型LPSO構造の材料科学 −次世代軽量構造材料へのイノベーション− 19 - 22 2013年01月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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High-temperature compressive deformation behavior of Mg97Zn1Y2 extruded alloy containing a long-period stacking ordered (LPSO) phase 査読あり
K. Hagihara, A. Kinoshita, Y. Fukusumi, M. Yamasaki, Y. Kawamura
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING 560 71 - 79 2013年01月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCIENCE SA
It has recently been found that Mg97Zn1Y2 extruded alloy containing a long-period stacking ordered (LPSO) phase has superior mechanical properties. In this study, the high-temperature deformation mechanism of the Mg97Zn1Y2 extruded alloy was examined. Grain-boundary strengthening due to the refined Mg-matrix phase and fiber-like reinforcement due to the LPSO phase dominantly contribute to the strengthening of the alloy at room temperature, and they were confirmed to effectively act even at 200 degrees C. As a result, the extremely high strength of the alloy is maintained up to 200 degrees C, unlike other conventional Mg alloys. At 300 degrees C, however, the yield stress of the Mg97Zn1Y2 alloy largely decreases, and the orientation and the grain size dependence of the yield stress become weak. Increases in the operation frequency of non-basal slip in the Mg-matrix grains weaken the grain-boundary strengthening effect. In addition, the effect of fiber-like reinforcement due to the LPSO phase is also weakened at 300 degrees C because the window of microstructure suitable for inducing this effect becomes significantly narrow at this temperature. (C) 2012 Elsevier B.V. All rights reserved.
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OS0413 LPSO相, HCP結晶におけるキンク変形の実験的考察
萩原 幸司, 本浪 雅史, 伊津野 仁史, 中野 貴由, 山崎 倫昭, 河村 能人
M&M材料力学カンファレンス 2013 ( 0 ) _OS0413 - 1_-_OS0413-2_ 2013年
記述言語：日本語 掲載種別：研究論文（その他学術会議資料等） 出版者・発行元：一般社団法人 日本機械学会
The deformation behavior accompanied by the formation of deformation kink in synchronized LPSO-phase was examined by comparing the behavior in the hcp-Zn single crystal. Deformation process of the LPSO phase DS crystal accompanied by the formation of deformation kink was investigated by dynamical observation and the features were compared to that in Zn single crystal. In both crystals the formation of deformation kink bands were confirmed in specimens that were compressed along the direction parallel to the basal plane. The characteristic features of the deformation kink band showed many similarities in them.
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Phase-field simulation of lamellar structure formation in MoSi <inf>2</inf>/NbSi<inf>2</inf> duplex suicide 査読あり
Yuichiro Koizumi, Toshihiro Yamazaki, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki Inui
Materials Research Society Symposium Proceedings 1516 309 - 315 2013年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス）
We conducted phase-field simulations of microstructural evolution in C11b-MoSi2 / C40-NbSi2 dual phase alloy with and without Cr-addition to examine the factors responsible for the formation and stability of the lamellar structure on the basis of thermodynamics, micromechanics and first-principles calculations. The first principles calculation was used for evaluating the interfacial energy, segregation energy of solute Cr-atoms and lattice parameters of imaginary disilicides for estimating the effects of solute distribution on the lattice misfit. When both of lattice misfit and the anisotropy of interfacial energy is taken into account, a lamellar structure similar to that observed experimentally is formed. In the absence of Cr-addition, the straightness of lamellar structure decreased slightly. When an isotropic interfacial energy is assumed, lamellar structure is not formed. Instead, a microstructure with habit planes parallel to {1 0 1 1} plane of C40-phase is formed. Thus, the anisotropy of interfacial energy is crucial for the lamellar structure formation rather than the elastic energy due to lattice misfit. © 2013 Materials Research Society.
DOI： 10.1557/opl.2013.360
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Phase-field study on the segregation mechanism of additive elements in NbSi<inf>2</inf>/MoSi<inf>2</inf> duplex suicide 査読あり
Toshihiro Yamazaki, Yuichiro Koizumi, Akihiko Chiba, Koji Hagihara, Takayoshi Nakano, Koretaka Yuge, Kyosuke Kishida, Haruyuki Inui
Materials Research Society Symposium Proceedings 1516 145 - 150 2013年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス）
We have examined segregation behavior of various alloying elements at lamellar interfaces of C40-NbSi2/C11b-MoSi2 duplex suicide by a phase-field simulation, which takes into account not only bulk chemical free energy but also segregation energy evaluated by the first principles calculation to reflect interaction between solutes and interface. The simulation suggests that segregation behaviors greatly depend on additive elements. In the case of Cr-addition, the C40-phase becomes enriched with Nb and Cr, while the C11b-phase becomes enriched with Mo, which agrees with the equilibrium phase diagram. Slight segregation of Cr atoms is observed at the interface, whereas Nb and Mo concentrations monotonically change across the diffuse interface between C11b and C40 phases. Significant segregations of Zr and Hf are formed at static interfaces, which are attributed to the chemical interaction between solute atoms and the static interface. © 2013 Materials Research Society.
DOI： 10.1557/opl.2013.391
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Compression of micro-pillars of a long period stacking ordered phase in the Mg-Zn-Y system 査読あり
Atsushi Inoue, Kyosuke Kishida, Haruyuki Inui, Koji Hagihara
Materials Research Society Symposium Proceedings 1516 151 - 156 2013年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス）
Deformation behavior of an 18R-type long period stacking ordered (LPSO) phase in the Mg-Zn-Y system was studied by micro-pillar compressions of single crystalline specimens prepared by focused ion beam (FIB) technique as a function of loading axis orientation and specimen dimensions. When the loading axis is inclined to the basal plane of the LPSO phase by 42°, basal slip of (0001)〈1120〉-type is activated irrespective of the specimen dimensions. When the loading axis is parallel to the basal plane, the formation of thick deformation bands are observed for all specimens tested. Strong size-dependence of yield stress values is observed for both types of micro-pillar specimens with different loading axis orientations. © 2013 Materials Research Society.
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Non-basal slip systems operative in Mg12ZnY long-period stacking ordered (LPSO) phase with 18R and 14H structures 査読あり
K. Hagihara, Y. Fukusumi, M. Yamasaki, T. Nakano, Y. Kawamura
Materials Transactions 54 ( 5 ) 693 - 697 2013年
記述言語：英語 掲載種別：研究論文（学術雑誌）
Non-basal slip systems in the Mg12ZnY long-period stacking ordered (LPSO) phase, the operational frequency of which is increased at high-temperatures and affects the mechanical properties, were clarified. The {1100}(1120) prism slip was identified in both 18R and 14H LPSO phases, even though they have the different lattice systems. This behavior is different from that observed in a Ni-based LPSO phase. The peculiar chemical modulation in the Mg12ZnY LPSO phase may affect the selection of operative slip systems. © 2013 The Japan Institute of Metals and Materials.
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Biocompatible low Young's modulus achieved by strong crystallographic elastic anisotropy in Ti-15Mo-5Zr-3Al alloy single crystal 査読あり
S. -H. Lee, M. Todai, M. Tane, K. Hagihara, H. Nakajima, T. Nakano
JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS 14 48 - 54 2012年10月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCIENCE BV
The elastic anisotropy of the Ti-15Mo-5Zr-3Al (mass%) beta-Ti alloy, an ISO certified biomedical material, was investigated using its single crystal. It was revealed that the Young's modulus exhibited pronounced anisotropy. The Young's modulus was reduced to 44.4 GPa along the < 100 > direction in the Ti-15Mo-5Zr-3Al single crystal, that is comparable to that of human cortical bones. We determined the strategy that beta-Ti alloys with extremely low moduli can be developed by reducing the electron-atom (e/a) ratio in alloys, and by suppressing the formation of the omega-phase at the same time. This new knowledge must lead to the development of "single crystalline beta-Ti implant materials" as hard tissue replacements for reducing the stress shielding effect. (C) 2012 Elsevier Ltd. All rights reserved.
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シンクロ型LPSO相の塑性変形機構，Mg合金強化機構 招待あり
萩原幸司
日本機械学会2012年度年次大会 講演概要集 W012002 2012年09月
記述言語：日本語 掲載種別：研究論文（その他学術会議資料等）
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ミニ特集「若手研究者からみた研究教育のグローバル化とこれからの日本の材料科学」 査読あり
波多聰, 廣澤渉一, 村上恭和, 井誠一郎, 萩原幸司, 中川惠友, 池田賢一, 松田光弘, 宮野公樹, 塗溶
まてりあ 51 453 - 454 2012年05月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Microstructural and Orientation Dependence of the Plastic Deformation Behavior in beta-type Ti-15Mo-5Zr-3Al Alloy Single Crystals 査読あり
Sang-Hoon Lee, Koji Hagihara, Takayoshi Nakano
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE 43A ( 5 ) 1588 - 1597 2012年05月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：SPRINGER
The plastic deformation behavior of a beta-type Ti-15Mo-5Zr-3Al alloy with a body-centered cubic (bcc) structure, which is a promising material for biomedical applications, was investigated. The orientation dependence of the plastic deformation behavior was examined by using a single crystal. In addition, changes in the mechanical properties depending on the microstructure were examined. The beta single phase was maintained even after short-time annealing below 673 K (400 A degrees C). Thus, the variations in the mechanical properties were small. However, an ellipsoidal omega phase and a lath-like alpha phase were precipitated in long-time annealing at 573 K (300 A degrees C) and 673 K (400 A degrees C), leading to large increases in the yield stress. For the deformation behavior, a dislocation with a Burgers vector parallel to < 111 > was observed irrespective of the heat-treatment conditions and loading orientations. However, the observed slip plane changed considerably depending on the loading axis, and the yield stress exhibited a strong orientation dependence because of the dislocation core structure effect in the bcc-structured crystals. The physical properties of Mo, which is the main constituent atom in the current alloy, may strongly affect the dislocation core structure and induce the characteristic orientation dependence of the plastic behavior.
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First-principles study on phase stability of MoSi2-NbSi2 pseudobinary alloys 査読あり
Koretaka Yuge, Yuichiro Koizumi, Koji Hagihara, Takayoshi Nakano, Kyosuke Kishida, Haruyuki Inui
PHYSICAL REVIEW B 85 ( 13 ) 134106 2012年04月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：AMER PHYSICAL SOC
The phase stability of MoSi2-NbSi2 pseudobinary alloys was examined by Monte Carlo simulation and the cluster expansion technique based on first-principles calculations. We found that formation energies of all possible atomic arrangements exhibited a positive sign, indicating that no stable intermediate phase exists between MoSi2 with C11(b) and NbSi2 with C40 structures. The C40 phase has significantly greater solubility as well as higher temperature dependence of solubility than C11b, which agrees with previous experimental reports. Lattice vibration is found to significantly affect the solubility of both C11(b) and C40 phases, where its impact naturally increases at higher temperatures. From the analysis of Warren-Cowley short-range-order parameters, the C11(b) single phase can be interpreted as a nearly disordered state, while the C40 phase exhibits explicit deviation from the disordered state: C40 prefers Mo-Mo and Nb-Nb like-atom pairs for first-nearest-neighbor coordination, especially around equiatomic composition.
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OS0306 HCP金属,シンクロ型LPSO相におけるキンク変形
萩原 幸司, 福住 嘉浩, 中野 貴由, 山崎 倫昭, 河村 能人
M&M材料力学カンファレンス 2012 ( 0 ) _OS0306 - 1_-_OS0306-2_ 2012年
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：一般社団法人 日本機械学会
The deformation behavior accompanied by the formation of deformation kink in synchronized LPSO-phase was examined by comparing the behavior in the hcp-Zn single crystal. The features of the band like deformation product in LPSO-phase is similar to those of the deformation kink proposed in Zn single crystal, suggesting that the similar mechanism may govern the formation behavior of the deformation kink. However, the size of the deformation band and the migration speed of the interface were largely different between them. This implies that the crystal structure, morphology of the grain, loading orientation, etc. may affect the formation behavior of the deformation kink.
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Single Crystal Growth and its Microstructure in Co-Cr-Mo alloys for Biomedical Applications 査読あり
Takayoshi Nakano, Keita Sasaki, Koji Hagihara, Takuya Ishimoto, Yusuke Fujii, Ai Serizawa
THERMEC 2011, PTS 1-4 706-709 561 - + 2012年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：TRANS TECH PUBLICATIONS LTD
Co-Cr-Mo based alloys have been widely employed as heat resistant materials and as biomaterials for implants because of their high strength and superior wear resistance. In general, the alloys exhibit a very complicated composition-dependent microstructure containing stacking faults and related mechanical properties. Thus, the essential properties must be clarified by using not only polycrystals but also single crystals. To our knowledge, single crystals and related properties have not been reported elsewhere. Thus, Co-Cr-Mo single crystals were grown and used to analyze the microstructure and the related properties.
Single crystals with a composition Co-27 mass% Cr-6 mass% Mo alloy defined by ASTM F75 were grown by two single crystal apparatuses: the optical floating zone and the Bridgman methods. The single crystals with the smooth-surface shape were successfully obtained in the Bridgman method under an Ar gas atmosphere at a crystal growth rate of 5.0 or 2.5 mm/h.
A portion of the crystals contain Al as Al2O3 precipitates from the crucible. Since the Al2O3 precipitate induces martensitic phase transformation from fcc (gamma) phase to hcp (epsilon) phase, the single crystals were separated into two parts (a) containing Al2O3 precipitate and (b) in the absence of the clear precipitate. The microstructure was significantly altered by the martensitic phase transformation from the gamma to epsilon phase induced by stress field or heating. In addition, variant formation of E phase has a large influence on the mechanical functions of these Co-Cr-Mo alloys. Novel findings were preliminary obtained in the single crystals. -
Microstructural factors affecting the deformation behavior of Mg12ZnY LPSO-phase alloys 査読あり
Koji Hagihara, Akihito Kinoshita, Yoshihiro Fukusumi, Michiaki Yamasaki, Yoshihito Kawamura
THERMEC 2011, PTS 1-4 706-709 1158 - + 2012年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：TRANS TECH PUBLICATIONS LTD
Microstructural factors that govern the plastic deformation of the long-period stacking ordered (LPSO) phase were clarified. The decrease in length of the long-axis for the plate-like shape of LPSO-phase grains increases the yield stress of the alloy in which basal slip is predominant in deformation. On the other hand, the yield stress tended to increase as the thickness of the plate-like shapes of the grains decreased for the alloy in which the formation of deformation kinks carried the strain.
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Fracture behavior and toughness of NbSi2-based single crystals and MoSi2(C11(b))/NbSi2(C40) duplex crystals with a single set of lamellae 査読あり
K. Hagihara, T. Nakano
ACTA MATERIALIA 59 ( 10 ) 4168 - 4176 2011年06月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
The fracture behavior and toughness of (Mo0.85Nb0.15)Si-2 suicide crystals were investigated by three-point bending tests. Crystals with two different microstructures, namely the C40 single-phase single-crystalline form and MoSi2(C11(b))/NbSi2(C40) duplex crystals with an oriented single set of lamellae, were prepared, and their fracture behaviors were compared. The duplex microstructure improved the toughness, exhibiting higher values than the C40 single-phase single crystals at almost all loading orientations. An increase of more than 20% in the fracture toughness was obtained in a duplex specimen, A-2, in which the lamella boundaries are parallel to the side surface and have a notch face parallel to (1 (2) over bar 1 0)(C40). A complicated morphology appeared in the fracture surface of specimen A-2 as a result of significant deflection of crack propagation. Crack deflection occurred predominantly along the plane parallel to {1 0 (1) over bar 0} cleavage planes in the constituent C40 phase. The C11b lamella effectively prevented the initial rapid propagation of cracks along the notched plane, because the ease of gliding of its dislocations and its deformability effectively accommodated stress concentration. This induced crack deflection, resulting in improved fracture toughness. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Plastic Deformation Behavior of Mg12ZnY LPSO-Phase with 14H-Typed Structure 査読あり
K. Hagihara, Y. Sugino, Y. Fukusumi, Y. Umakoshi, T. Nakano
MATERIALS TRANSACTIONS 52 ( 6 ) 1096 - 1103 2011年06月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：JAPAN INST METALS
We investigated the influence of a change in the stacking sequence of the close-packed plane in a Mg12ZnY long-period stacking ordered (LPSO) phase on its mechanical properties. A 14H-typed LPSO-phase crystal was fabricated by annealing a directionally solidified (DS) crystal with a 18R-typed LPSO-structure at 525 degrees C for 3 days, and the temperature dependence and orientation dependence of the yield stress were examined via compression tests. (0001)< 11 (2) over bar0 > basal slip was identified as a dominant deformation mode, and deformation kink bands were formed under compression in the case of suppression of basal slip motion. The deformation mechanism of the 14H-typed LPSO-phase is almost similar to that of the 18R-typed LPSO-phase, even though a slight difference was observed at temperatures above 300 degrees C. [doi:10.2320/matertrans.MC201007]
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Effect of multimodal microstructure evolution on mechanical properties of Mg-Zn-Y extruded alloy 査読あり
Michiaki Yamasaki, Kenji Hashimoto, Koji Hagihara, Yoshihito Kawamura
ACTA MATERIALIA 59 ( 9 ) 3646 - 3658 2011年05月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
A high strength Mg-Zn-Y alloy featuring increased ductility and a multimodal microstructure is developed. The microstructure of the extruded Mg-Zn-Y alloy consists of three regions: a dynamically recrystallized alpha-Mg fine-grain region with random orientation; a hot-worked alpha-Mg coarse-grain region with strong basal texture; and a long-period stacking ordered (LPSO) phase grain region. Having found that bimodal microstructure evolution in the alpha-Mg matrix is influenced by the morphology of the LPSO phase in the as-cast state, the authors investigate the effect of secondary dendrite arm spacing (SDAS) in the cast state on the microstructure evolution and mechanical properties of the extruded Mg-Zn-Y alloy. Mg-Zn-Y alloy ingots with various SDAS are obtained by temperature-controlled solidification techniques at various cooling rates. Mg-Zn-Y ingots are extruded at 623 K and an extrusion ratio of 10. A decrease in SDAS is associated with dynamic recrystallization of the alpha-Mg phase region and a high dispersion of fiber-shaped LPSO phase during extrusion. An increase in dynamically recrystallized alpha-Mg grains with very weak texture improves ductility; the effective dispersion of the hot-worked alpha-Mg grains with a strong basal texture and the fiber-shaped LPSO phase grains conspire to strengthen the alloy. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Effects of Cr-addition and lamellar microstructure on the oxidation behavior of single crystal (Mo0.85Nb0.15)Si-2 査読あり
Ou Zhu, Lanting Zhang, Jinxing Yu, Aidang Shan, Jiansheng Wu, Koji Hagihara, Takayoshi Nakano
JOURNAL OF ALLOYS AND COMPOUNDS 509 ( 5 ) 1511 - 1516 2011年02月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCIENCE SA
The oxidation behavior of (Mo0.85Nb0.15)Si-2 single crystals and the influence of Cr-addition were studied focusing on its microstructure dependence. Cr-addition to single-phase C40-structured (Mo0.85Nb0.15)Si-2 crystal induced the formation of crystalline silica, leading to slightly larger weight gain during the oxidation test at 1200 degrees C. Furthermore, Cr-addition to C40/C11(b) duplex-phase (Mo0.85Nb0.15)Si-2 crystal with lamellar structure strongly suppressed the internal oxidation of the C11(b) phase, resulting in excellent oxidation resistance. C40/C11(b) lamellae-structured crystals showed better oxidation resistance than the C40-structured crystals. (C) 2010 Elsevier B.V. All rights reserved.
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OS2017 Mg基LPSO相の塑性挙動に及ぼす組織学的因子(OS20-3 チタンおよびLPSO型マグネシウム合金,OS-20 HCP金属の実験力学と計算力学)
萩原 幸司, 木下 昭人, 福住 嘉浩, 山崎 倫昭, 河村 能人
M&M材料力学カンファレンス 2011 ( 0 ) _OS2017 - 1_-_OS2017-2_ 2011年
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：一般社団法人 日本機械学会
Microstructural factors that govern the plastic deformation of the long-period stacking ordered (LPSO) phase were examined. The decrease in length of the long-axis for the plate-like shape of LPSO-phase grains increases the yield stress of the alloy in which basal slip is predominant in deformation. On the other hand, the yield stress tends to increase as the thickness of the plate-like shapes of the grains decreases for the alloy in which the formation of deformation kinks carries the strain.
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Low Young’s modulus of Ti-Nb-Ta-Zr alloys caused by softening in shear moduli c′ and c44 near lower limit of body-centered cubic phase stability 査読あり
M. Tane, S. Akita, T. Nakano, K. Hagihara, Y. Umakoshi, H. Mori, H. Nakajima
Acta Materialia 58 ( 20 ) 6790 - 6798 2010年12月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Effect of long-period stacking ordered phase on mechanical properties of Mg97Zn1Y2 extruded alloy 査読あり
K. Hagihara, A. Kinoshita, Y. Sugino, M. Yamasaki, Y. Kawamura, H. Y. Yasuda, Y. Umakoshi
ACTA MATERIALIA 58 ( 19 ) 6282 - 6293 2010年11月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
The mechanical properties of Mg97Zn1Y2 extruded alloy, composed of Mg matrix phase and a long-period stacking ordered phase, the so-called LPSO phase, with a volume fraction of approximately 24%, were investigated using compression tests at room temperature. The microstructure was varied to a large degree by various heat treatments at high temperatures above 400 degrees C, and the relationship between the microstructure and mechanical properties was clarified. The plastic behavior of the Mg,/LPSO two-phase alloy was compared with that of Mg99.2Zn0.2Y0.6 alloy, composed almost Mg-solid-solution phase, and the strengthening mechanisms at work in the Mg97Zn1Y2 extruded alloy are discussed. The existence of the LPSO phase strongly enhanced the refinement of Mg matrix grains during extrusion, which led to a large increase in yield stress through the Hall-Petch relationship. In addition, the LPSO phases, which were aligned along the direction of extrusion in the Mg97Zn1Y2 extruded alloy, acted as hardening phases, being roughly coordinated with the short-fiber reinforcement mechanism. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Effect of Extrusion Parameters on Mechanical Properties of Mg97Zn1Y2 Alloys at Room and Elevated Temperatures 査読あり
Masaaki Hirano, Michiaki Yamasaki, Koji Hagihara, Kenji Higashida, Yoshihito Kawamura
MATERIALS TRANSACTIONS 51 ( 9 ) 1640 - 1647 2010年09月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：JAPAN INST METALS
The effects of alloy extrusion parameters such as extrusion ratio temperature and speed on the mechanical properties at room and elevated temperatures and the microstructure evolution were investigated in the production of high strength Mg-Zn Y alloys The alloy used is a Mg97Zn1Y2 (at%) which is engineered to acquire a long period stacking ordered (LPSO) structure phase to increase alloy strength The microstructure of the extruded Mg97Zn1Y2 alloy consists of hot-worked and dynamically recrystallized (DRXed) alpha Mg grains that includes a fiber shaped LPSO phase elongated along the direction of extrusion Whereas an increase in average equivalent strain promotes the DRX of alpha-Mg matrix and the dispersion of the fiber shaped LPSO phase an increase in average metal flow rate is conductive to the DRX of alpha-Mg grams but is not to the dispersion of LPSO phase The mechanical properties of the extruded Mg Zn Y alloys are affected by changes in the area fraction of the DRXed grains and the dispersion of the fiber-shaped LPSO phase As the extrusion ratio and extrusion speed increase overall DRX bringing gram growth in its train in the alpha Mg matrix phase decreases the tensile strength of alloys, but the dispersed fiber shaped LPSO phase remaining in the DRXed grains region makes good the adverse effect of overall DRX followed by grain growth [doi 10 2320/matertrans MAW201026]
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Plastic deformation behavior of Mg97Zn1Y2 extruded alloys 査読あり
K. Hagihara, A. Kinoshita, Y. Sugino, M. Yamasaki, Y. Kawamura, H. Y. Yasuda, Y. Umakoshi
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA 20 ( 7 ) 1259 - 1268 2010年07月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCIENCE BV
The mechanical properties of the Mg97Zn1Y2 extruded alloy containing the long-period stacking ordered phase, the so-called LPSO-phase, with a volume fraction of 24%-25%, were examined by compression tests and cyclic tension compression deformation tests. The plastic behavior of the extruded alloys with compositions of Mg99.2Zn0.2Y0.6 and Mg89Zn4Y7 (molar fraction, %), which were almost the same compositions of Mg matrix phase and LPSO phase in Mg97Zn1Y2 Mg/LPSO two-phase alloy, respectively, were also prepared. By comparing their mechanical properties, the strengthening mechanisms operating in the Mg97Zn1Y2 extruded alloy were discussed. Existence of the LPSO-phase strongly enhanced the refinement of Mg matrix grain size during extrusion, which led to a large increment of the strength of alloy. In addition, the LPSO-phases, which were aligned along the extrusion direction in Mg97Zn1Y2 extruded alloy, acted as hardening phases, just like reinforced fibers.
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Plastic deformation behavior of Mg89Zn4Y7 extruded alloy composed of long-period stacking ordered phase 査読あり
K. Hagihara, A. Kinoshita, Y. Sugino, M. Yamasaki, Y. Kawamura, H. Y. Yasuda, Y. Umakoshi
INTERMETALLICS 18 ( 5 ) 1079 - 1085 2010年05月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCI LTD
The deformation behavior of an Mg89Zn4Y7 (at.%) extruded alloy composed mostly of the long-period stacking ordered (LPSO) phases, was investigated at room temperature. Several heat-treatments were conducted for the extruded alloy in the temperature range between 400 and 525 degrees C, and the correlation between the microstructure and the mechanical properties were quantitatively examined. The yield stress of the as-extruded alloy showed extremely high value of similar to 480 MPa. The deformation of the as-extruded alloy proceeded accompanied by the formation of deformation kinks and small amounts of non-basal slips. The microstructure of the extruded alloy was highly thermally stable and the yield stress showed little change by heat-treatments below 400 degrees C. However, the yield stress was gradually decreased by annealing above 400 degrees C. The yield stress of the alloys annealed at and above 475 degrees C showed discontinuous decreases with increasing annealing temperature. The yield stress of the annealed specimens could be estimated by the Hall-Petch relationship by regarding the length of the long-axis of plate-like grains as the grain size. This suggests that the basal (0001) slip governed the plastic behavior of the LPSO-phase alloy composed of randomly oriented grains. (C) 2010 Elsevier Ltd. All rights reserved.
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Improvement of aligned lamellar structure by Cr-addition to NbSi2/MoSi2 duplex-silicide crystals 査読あり
K. Hagihara, T. Nakano, S. Hata, O. Zhu, Y. Umakoshi
SCRIPTA MATERIALIA 62 ( 8 ) 613 - 616 2010年04月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
The addition of Cr to (Mo0.85Nb0.15)Si-2 crystals significantly improves the thermal stability of the lamellar structure composed of C11(b)-MoSi2 and C40-NbSi2 phases. Analysis using electron microscopy indicates the segregation of Cr atoms at the C40/C11(b) lamellar interface. This leads to a decrease in the lattice misfit strain at the interface and better thermal stability of the lamellae. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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Plastic deformation behavior of Ni-3(Ti0.7Nb0.3) single crystals with D0(19) structure 査読あり
K. Hagihara, H. Fujimoto, T. Nakano, Y. Umakoshi
INTERMETALLICS 18 ( 4 ) 434 - 440 2010年04月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCI LTD
We have investigated the plastic deformation behavior of Ni-3(Ti0.7Nb0.3) crystals with the D0(19) structure in the temperature range of -196 to 1200 degrees C. The (0001) < 2<(1)over bar>(1) over bar0 > basal slip, {1 (1) over bar 00} < 11<(2)over bar>0 > prism slip, and {(2) over bar 111} < <(2)over bar>11 (6) over bar; > pyramidal slip are operative depending on the temperature and loading orientation. A strong yield stress anomaly (YSA) is caused by slip on the basal plane similar to that observed in other hcp-derivative geometrically close-packed (GCP) compounds such as D0(a)-Ni3Nb and D0(24)-Ni3Ti, due to the Kear-Wilsdorf (K-W) locking of screw dislocations. The features of YSA by basal slip, such as the profile of the temperature vs. critical resolved shear stress (CRSS) curve are quite similar in those Ni-3(Ti0.7Nb0.3), Ni3Nb, and Ni3Ti crystals; nevertheless, the profiles of the temperature vs. CASS curves observed in the case of prism slip are significantly different for each crystal. The results indicate that in the case of these hcp-derivative GCP compounds, although the K-W locking, which is the origin of YSA, accompanies the thermally activated cross-slip of the screw partial dislocations from the (0001) primary slip plane onto the {01 (1) over bar0} prism plane, the mobility of dislocations on the prism plane does not directly influence the YSA behavior of basal slip. (C) 2009 Elsevier Ltd. All rights reserved.
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Plastic deformation behavior of Mg12YZn with 18R long-period stacking ordered structure 査読あり
K. Hagihara, N. Yokotani, Y. Umakoshi
INTERMETALLICS 18 ( 2 ) 267 - 276 2010年02月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCI LTD
The recent development of high-strength Mg alloys has focused on the role of the strengthening phase with a long-period stacking ordered (LPSO) structure. In this study, the plastic deformation behavior of Mg12ZnY with an 18R LPSO-structure was investigated using directionally solidified crystals. The (0001)<11<(2)over bar>0> basal slip was identified to be the dominant operative deformation mode in Mg12ZnY, whose critical resolved shear stress (CRSS) was estimated to be 10-30 MPa. When the stress was loaded parallel to the (0001) plane, where the Schmid factor for the basal slip is negligible, deformation kinks were initiated in the specimens and accommodated the compressive strain to some extent. These results showed that the plastic behavior of LPSO Mg12ZnY is highly anisotropic and, hence, the control of the microstructure is expected to be extremely important in order to improve the mechanical properties of the LPSO-phases in high-strength Mg alloys. (C) 2009 Elsevier Ltd. All rights reserved.
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Change in Microstructure by Heat-treatment and Corresponding Deformation Behavior in Ni3V Single Crystals 査読あり
Koji Hagihara, Mayumi Mori, Takuya Kishimoto, Yukichi Umakoshi
THERMEC 2009, PTS 1-4 638-642 1318 - + 2010年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：TRANS TECH PUBLICATIONS LTD
D0(22)-Ni3V contains three variants whose [001] c-axes are mutually perpendicular In addition, due to the order-disorder transition the anti-phase domains (APD) are also introduced under some heat-treatment conditions In this study, the influence of such microstructures; the size of variants and APDs, on the plastic deformation behavior of Ni3V was investigated by using single crystals, in which the microstructure was variously controlled by heat-treatments
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Temperature Dependence of Compressive Deformation Behavior of Mg89Zn4Y7 Extruded LPSO-Phase Alloys 査読あり
Koji Hagihara, Akihito Kinoshita, Yuya Sugino, Michiaki Yamasaki, Yoshihito Kawamura, Hiroyuki Y. Yasuda, Yukichi Umakoshi
PRICM 7, PTS 1-3 654-656 607 - + 2010年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：TRANS TECH PUBLICATIONS LTD
Deformation mechanisms of Mg89Zn4Y7 (at.%) extruded alloy, which is mostly composed of LPSO-phase, was investigated focusing on their temperature dependence. The yield stress of as-extruded alloy showed extremely high value of similar to 480 MPa at RT, but it largely decreased to similar to 130 MPa at 300 degrees C. The decreasing rate of the yield stress could be significantly reduced, however, by the annealing of specimen at 400 degrees C, by suppressing the microyielding which is considered to occur related by the grain boundary sliding in restricted regions. The yield stress of the annealed specimens with random textures could be estimated by the liall-Petch relationship by regarding the length of long-axis of plate-like grains as a grain size between RT and 300 degrees C. The yield stress of the annealed specimens maintained high values even at 200 degrees C, but it also showed large decreases at 300 degrees C.
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Multimodal Microstructure Evolution in Wrought Mg-Zn-Y Alloys with High Strength and Increased Ductility 査読あり
Michiaki Yamasaki, Kenji Hashimoto, Koji Hagihara, Yoshihito Kawamura
PRICM 7, PTS 1-3 654-656 615 - + 2010年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：TRANS TECH PUBLICATIONS LTD
High strength and ductile Mg96Zn2Y2 (at%) alloys with multi-modal microstructure are developed. Microstructure of the extruded Mg96Zn2Y2 alloy consists of three regions; the dynamically recrystallized alpha-Mg fine-grains region, the hot-worked alpha-Mg coarse-grains region elongated along extrusion direction, and the long-period stacking ordered (LPSO) phase region with kink deformation bands. Bimodal microstructure evolution in alpha-Mg matrix is influenced by the morphology of the LPSO phase in the as-cast state, therefore, the effect of secondary dendrite arm spacing in cast state on the microstructure evolution and mechanical properties of the extruded Mg-Zn-Y alloy is investigated. An increase in the dynamically recrystallized grains improves ductility of the extruded alloys; the effective dispersion of the LPSO phase enhances strengthening of the alloy.
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Controlling factors on the fatigue behaviour of Ti-Nb-Ta-Zr alloys single crystals 査読あり
K.Hagihara, T.Nakano, M.Niinomi
Proc. of PFAM 18 (Processing and Fabrication of Advanced Materials 1023 - 1030 2009年12月
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス）
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Oxygen Distribution in Titanium Single Crystal Fabricated by Optical Floating-Zone Method under Extremely Low Oxygen Partial Pressure 査読あり
Koji Hagihara, Takahiro Tachibana, Keita Sasaki, Yoshiyuki Yoshida, Naoki Shirakawa, Tohru Nagasawa, Takayuki Narushima, Takayoshi Nakano
MATERIALS TRANSACTIONS 50 ( 12 ) 2709 - 2715 2009年12月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：JAPAN INST METALS
This study examines the properties of a titanium single crystal fabricated by the floating-zone-melting process in Ar gas flow atmosphere where the partial pressure of oxygen was maintained extremely low at P-O2 = similar to 10(-23) atm by the newly developed oxygen pump system. The distribution of solute oxygen atoms in the obtained single crystal exhibited a peculiar gradient. In the early stage of the titanium single crystal growth, the oxygen content in the single crystal (approximately 1600 ppm) was higher than that in the mother ingot (980 ppm). However, as the crystal growth progressed. the oxygen content gradually decreases and then reduced to 660 ppm in the final stage of crystal growth. Such a gradient of oxygen composition was not detected in titanium single crystals fabricated under conventional, commercial Ar gas flow atmosphere. owing to the unique gradient of oxygen content formed under extremely low oxygen partial pressure, the Vickers hardness of the single crystal decreased gradually along the crystal growth direction. [doi: 10.2320/matertrans.MA200903]
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Mg12ZnY長周期相の塑性変形機構、Mg合金強化機構 査読あり
萩原幸司, 木下昭人, 杉野裕也, 山崎倫昭, 河村能人, 馬越佑吉
日本機械学会 M&M2009材料力学カンファレンス論文集 2009年07月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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RELATION BETWEEN THE MICROSTRUCTURE AND THE PLASTIC DEFORMATION BEHAVIOR IN Mg12ZnY WITH LPSO STRUCTURE 査読あり
Koji Hagihara, Akihito Kinoshita, Yuya Sugino, Naoyuki Yokotani, Michiaki Yamasaki, Yoshihito Kawamura, Yukichi Umakoshi
MAGNESIUM TECHNOLOGY 2009 477 - + 2009年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：MINERALS, METALS & MATERIALS SOC
Plastic deformation behavior of Mg12ZnY with long-period stacking ordered (LPSO) structure of basal plane, called LPSO-phase, was examined using three single-phase alloys of directionally solidified (DS), as-solidified and extruded alloys with different microstructures at room temperature.
By using DS alloy, the dominantly operative deformation mode in LPSO-phase was identified to be (0001)<11<(2)over bar>0> basal slip. In compression parallel to the growth direction where the Schmid factor for the basal slip is negligible, on the other hand, the deformation proceeds accompanied by the formation of deformation kink, leading to higher yield stress than those at other loading axes.
The yield stress of as-solidified alloy, in which LPSO-phase grains show relatively large plate-like morphology but no texture, exhibits low value of around 110MPa at RT, due to the frequent operation of basal slip. On the other hand, the yield stress of extruded alloy shows much higher value than others accompanied by strong orientation dependence. The refined microstructure in extruded alloys effectively hinders the operation of basal slip, resulting in large increase in yield stress. -
OS0316 Mg_<12>ZnY長周期相の塑性変形機構,Mg合金強化機構(非立方晶型金属材料の変形現象とそのモデル化,オーガナイズドセッション)
萩原 幸司, 木下 昭人, 山崎 倫昭, 河村 能人, 馬越 祐吉
M&M材料力学カンファレンス 2009 ( 0 ) 732 - 733 2009年
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：一般社団法人 日本機械学会
Recently, the role of the strengthening phase with a long-period stacking ordered (LPSO) structure is focused for development of high-strength Mg alloys. In this study, the plastic deformation behavior of Mg_<12>ZnY with 18R LPSO-stnicture was investigated and the strengthening mechanism of the Mg/LPSO two-phase alloys was discussed. The (0001)<1120> basal slip was identified to be the dominant operative deformation mode in the LPSO phase, and deformation kinks were initiated to accommodated the compressive strain. The results showed that the plastic behavior of LPSO-phase is highly anisotropic. The existence of LPSO-phase in Mg alloys induces the grain refmement of Mg matrix grains dunng extrusion. In addition, it effectively acts as a fiber-like strengthening phase in deformation along the extruded direction.
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Role of the Microstructure on the Deformation Behavior in Mg12ZnY With a Long-Period Stacking Ordered Structure 査読あり
K. Hagihara, N. Yokotani, A. Kinoshita, Y. Sugino, H. Yamamoto, M. Yamasaki, Y. Kawamura, Y. Umakoshi
ADVANCED INTERMETALLIC-BASED ALLOYS FOR EXTREME ENVIRONMENT AND ENERGY APPLICATIONS 1128 329 - + 2009年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：MATERIALS RESEARCH SOC
The influence of a heat-treatment on the plastic deformation behavior in Mg12ZnY with a long-period stacking ordered (LPSO) structure was investigated by using crystals grown by the Bridgman method. Annealing of the crystal at 798 K for 3 days induced the change in the crystal structure of Mg12ZnY from the 18-fold rhombohedral structure (18R) to the 14-fold hexagonal structure (14H). The plastic behavior of those LPSO crystals showed a large variation depending on the loading axis in both crystals, because of the limitation of operative deformation modes in them. The change in the stacking sequence in the LPSO crystals did not show a large influence on the plastic deformation behavior at room temperature.
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Influence of heat-treatment on microstructure and plastic deformation behavior in Ni3V single crystals with the D022 structure 査読あり
K. Hagihara, M. Mori, T. Kishimoto, Y. Umakoshi
Journal of Physics: Conference Series 165 12004 2009年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：Institute of Physics Publishing
The control of microstructure in Ni3V single crystals such as variant and anti-phase boundary (APD) was attempted by quenching from the disordered state followed by annealing at several temperatures. In the heat-treatments, the microstructure strongly varied depending on the quenching speed from the disordered state. In slow-quenching, the lamellar structure composed of two variants was developed after annealing, as reported in many polycrystalline samples. However, only one of three variants was preferentially grown in the specimen rapidly quenched from the disordered state followed by annealing. The yield stress of slow-quenched specimen showed more than twice the value of the fast-quenched specimen. © 2009 IOP Publishing Ltd.
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Single-crystal growth and plastic deformation behaviour of a Ti-15Mo-5Zr-3Al alloy for biomedical application 査読あり
S. H. Lee, K. Hagihara, M. H. Oh, T. Nakano
Journal of Physics: Conference Series 165 12086 2009年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：Institute of Physics Publishing
A Ti-15Mo-5Zr-3Al alloy with a bcc structure are promising materials for biomedical application and were examined. The focus of this study was on the effect of heat treatment on microstructure and plastic deformation behaviour using a single crystal. The single crystal was successfully obtained by a floating zone method at a crystal growth rate of 2.5 mm/h. A slip at the <
111>
dislocation was present irrespective of heat treatment at 573K or 673K for 1.2 ks or 300 ks. The yield stress at the [149] loading axis varied significantly depending on microstructure, especially from the precipitation of the a phase. Al addition suppresses generation of the σ phase and increases the yield stress at the same time. © 2009 IOP Publishing Ltd. -
極低酸素分圧雰囲気下でのTi単結晶の帯溶融育成 査読あり
萩原幸司, 橘 孝洋, 佐々木啓太, 吉田良行白川直樹, 長澤 亨, 成島尚之, 中野貴由
日本金属学会誌 72 ( 12 ) 928 - 934 2008年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Peculiar elastic behavior of Ti-Nb-Ta-Zr single crystals 査読あり
M. Tane, S. Akita, T. Nakano, K. Hagihara, Y. Umakoshi, M. Niinomi, H. Nakajima
ACTA MATERIALIA 56 ( 12 ) 2856 - 2863 2008年07月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
The cause of a low Young's modulus was investigated in quaternary P-type Ti-Nb-Ta-Zr alloys, as the modulus is decreased to prevent bone absorption and degradation of bone quality when these alloys are implanted into human bones. This investigation was carried out using the alloys' single crystals. Acoustic measurements and analysis by the Hill approximation revealed that a low Young's modulus in a polycrystalline form is caused by the low shear modulus c', related to the low P-phase stability, low c(44), and relatively low bulk modulus B compared with those of binary Ti-based alloys. Furthermore, it was found that the single crystals had strong orientation dependence on Young"s modulus, where that in the < 100 >-direction E-100 is the lowest of all crystallographic orientations. For quaternary Ti29Nb-13Ta-4.6Zr alloy (mass%), E-100 is only similar to 35 GPa, which is similar to Young's modulus of human cortical bones as a result of the low B and c'. These results indicate that decreases in c', c(44) and B are essential for decreasing Young's modulus of novel beta-type Ti alloys which are expected to be developed in the near future. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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長周期積層構造相の力学特性、塑性変形挙動 招待あり
萩原幸司
日本金属学会分科会シンポジウム「長周期積層構造型マグネシウム合金の現状と今後の課題」 予稿 29 - 32 2008年05月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Fabrication and Plastic Deformation Behavior of Lamellar Ti-rich TiAl Crystals with Lotus-Type Aligned Pores 査読あり
T. Nakano, T. Tachibana, K. Hagihara, Y. Umakoshi, T. Ide, M. Tane, H. Nakajima
POROUS METALS AND METALLIC FOAMS: METFOAM 2007 213 - + 2008年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：DESTECH PUBLICATIONS, INC
Ti-rich TiAl crystals are a promising candidate as light-weight and heat-resistant materials for aerospace and automobile applications.
In this study, we fabricated Ti-48.0at.%Al (Ti-rich TiAl) crystals with lotus-type aligned pores, and examined the microstructure and plastic deformation behavior. We succeeded in obtaining the gamma/alpha(2) two-phase lamellar Ti-rich TiAl crystals with elongated pores aligned parallel to the heat transfer direction by the floating zone method under the pressure of hydrogen and helium mixed gas at a crystal growth :ate of 330 mu m/s. The as-grown and annealed crystals show a well-developed lamellar structure with a strict orientation relationship between the alpha(2) phase and six gamma variants in each grain. However, these crystals exhibit no strong texture of lamellar grains. The total pore volume and the mean pore diameter are approximately 52 % and 380 pm, respectively.
The macro-yield stress strongly depends on the loading axis relative to the elongated pore. When the loading axis is parallel and perpendicular to the elongated pore direction, the yield stress obeys K=1 and 2.5, respectively, in the equation of sigma=sigma(0)(1-P)(kappa), where a is the macro-yield stress with pores, sigma(0) is the macro-yield stress without pores and P is the volume fraction of pores. The difference of K value, K=1 and 2.5, indicates the change in deformation manner, i.e. macroscopically homogeneous and locally heterogeneous plastic deformation, respectively. The plastic deformation behavior was also investigated at elevated temperatures up to 1273 K. The relatively high stress was maintained independent of the loading axis up to around 1073 K. The K value shows no strong temperature dependence because aligned pores give no change in deformation behavior at elevated temperatures. -
Crystal growth and plastic deformation behavior of Ti-29Nb-13Ta-4.6Zr bcc-based single crystal 査読あり
T. Nakano, K. Hagihara, H. Maki, Y. Umakoshi, M. Niinomi
Proc. Ti-2007 JIMIC5 (Science and Technnology) 1437 - 1439 2007年06月
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス）
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Effect of bcc-phase stability on cyclic deformation behavior in beta-type Ti-Nb-Ta-Zr alloys single crystals with different Nb content 査読あり
K. Hagihara, T. Nakano, A. Sonoura, K. Watanabe, Y. Umakoshi, M. Niinomi
Proc. in Ti-2007 1445 - 1447 2007年06月
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス）
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Effect of C11(b)-Stabilized element on deformation mode in C40-type (Nb1-xMox)Si-2 (x=0-0.85) single crystals
Takayoshi Nakano, Koji Hagihara, Yukichi Umakoshi
ADVANCED INTERMETALLIC-BASED ALLOYS 980 297 - + 2007年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：MATERIALS RESEARCH SOC
Plastic deformation behavior and the dominant deformation mode in ternary (Nb1-xMox)Si-2 (x=0-0.85) single crystals with the C40 structure were examined focusing on the phase stability between the C40 and C11(b) structures. Temperature dependence of CRSS for the (0001) < 2 (1) over bar(1) over bar0] slip is strongly influenced by the Mo concentration accompanied by the change in the dissociation mode from the co-planar-type to the synchroshear-type. In the ternary crystals with x=0-0.30, anomalous strengthening clearly appeared, and the peak stress increased up to 1600 degrees C with an increase in the Mo content. Mo atoms may gather and form a dragging atmosphere around 1/3 < 2 (1) over bar (1) over bar 0] dislocations containing a superlattice intrinsic stacking fault (SISF), resulting in anomalous strengthening. In contrast, in crystals with x=0.60-0.85, a high CRSS was obtained with fracture in a brittle manner at low temperatures, and the stress decreased remarkably with an increase in the test temperature. HRTEM observation showed that the synchroshear-type dissociation of each super-partial dislocation, 1/6 < 2 (1) over bar (1) over bar 0], occurred on the neighboring slip planes, accompanied by a much wider separation distance of SF than that in the ternary crystals with a low Mo content. This change in plastic deformation behavior may be closely related to the decrease in phase stability of the C40 structure with the addition of the C11(b)-stabilized element, Mo. The phase stability can be represented by the ratio of h/b, where h is the (0003) spacing and b is the amplitude of 1/3 < 2 (1) over bar (1) over bar 0 As the h/b ratio increases with the addition of Mo, the dissociation mode chances from the co-planar-type to the synchroshear-type at a ratio of 0.465.
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Microstructure and plastic deformation behavior of Ni3V single crystals 査読あり
Koji Hagihara, Mayumi Mori, Yukichi Umakoshi
PRICM 6: SIXTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-3 561-565 407 - + 2007年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：TRANS TECH PUBLICATIONS LTD
Plastic deformation behavior of Ni3V with D0(22) structure was examined using the single crystals containing two dominant variants of three. At [557] loading orientation, {111} 1/6 < 112] twinning is dominantly operative at low temperatures, but {111} 1/2 < 112] slip is activated at high temperatures accompanied by a rapid drop of yield stress.
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Microstructure and deformation behavior of lamellar Ti-rich TiAl crystal with lotus-type aligned pores 査読あり
Takayoshi Nakano, Takahiro Tachibana, Koji Hagihara, Yukichi Umakoshi, Takuya Ide, Masakazu Tane, Hideo Nakajima
PRICM 6: SIXTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-3 561-565 383 - + 2007年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：TRANS TECH PUBLICATIONS LTD
A porous Ti-48.0at.%Al (Ti-rich TiAl) crystal, in which lotus-type long cylindrical pores were aligned and (gamma/alpha(2)) two-phase lamellar structure was simultaneously developed, was fabricated by floating zone method under the pressure of hydrogen and helium mixed gas. Plastic deformation behavior and microstructure of the Ti-rich TiAl crystal with lotus-type aligned pores were investigated by focusing on the elongated pore direction. The as-grown and annealed crystals show a well-developed lamellar structure and no texture accompanied by 52% porosity and a mean pore diameter of 380 mu m. Yield stress strongly depends on the loading direction against the elongated pore. When loading directions are parallel and perpendicular to the pore direction, yield stresses obey K=1 and 2.5, respectively, in equation of sigma=sigma(0)(1-P)(K), where a is the yield stress with pores, sigma(0) is the yield stress without pores and p is porosity. This reflects macroscopically homogeneous and locally heterogeneous plastic deformation between pores, respectively.
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Plastic deformation behavior of oriented Ni3V crystals with D0(22) structure 査読あり
Koji Hagihara, Mayumi Mori, Yukichi Umakoshi
ADVANCED INTERMETALLIC-BASED ALLOYS 980 523 - + 2007年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：MATERIALS RESEARCH SOC
Plastic deformation behaviour of Ni3V with D0(22) structure was examined using the single crystals containing two dominant variants of three. Three deformation modes were confirmed to be operative depending on temperature and loading orientation. {111} 1/6 < 112] twinnng and/or {111} < 110] slip isa dominantly operative at low temperatures, but {111} 1/2 112] slip is activated at high temperatures accompanied by a rapid of yield stress.
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Effects of the anisotropy of the anti-phase boundary energy on the yield-stress anomaly in Ni3X compounds with close-packed crystal structures 査読あり
K. Hagihara, T. Tanaka, T. Nakano, P. Veyssiere, Y. Umakoshi
PHILOSOPHICAL MAGAZINE LETTERS 87 ( 10 ) 705 - 712 2007年
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：TAYLOR & FRANCIS LTD
This paper is aimed at clarifying the effects of the anisotropy of the anti-phase boundary (APB) energy on the yield-stress anomaly (YSA) of five distinct Ni-3(Ti, Nb) single crystals with various long-period ordered structures, in which the APB energy on the non-close-packed (non-CP) plane varies with changes in the stacking sequence of the close-packed planes. The APB energies of interest are estimated, based on a pair-wise interaction parameter model to the second neighbour. The YSA can be categorized in two groups of two and three compounds, within which the mechanical properties are nearly independent of composition. The microstructures resulting from deformation at 700 degrees C were compared. It is verified that the YSA is dominantly controlled by differences in the probability of locking by a Kear-Wilsdorf mechanism, which itself is governed by the anisotropy of APB energy in the non-CP planes relative to the primary slip plane.
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Ni3X型金属間化合物の結晶構造と塑性変形挙動 招待あり 査読あり
萩原幸司
まてりあ 45 813 - 816 2006年11月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Isothermal oxidation behavior of two-phase TiAl-Mn-Mo-C-Y alloys fabricated by different processes
Y Wu, SK Hwang, K Hagihara, Y Umakoshi
INTERMETALLICS 14 ( 1 ) 9 - 23 2006年01月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCI LTD
The isothermal oxidation behavior of two-phase Ti-46.6Al-1.4Mn-2Mo-0.3C-0.3Y based alloys in synthetic air at 800 and 900 degrees C was investigated. The main emphasis was focused on the effect of microstructures obtained by different processes of extrusion, melting and hot rolling, i.e. fully lamellar, nearly lamellar and duplex. On the exposure for 350 h at 800 degrees C, the growth rate and the spallation behavior of oxide scales of the alloys depended strongly on the fabrication process. The extruded alloy with a fine fully lamellar microstructure showed an excellent oxidation resistance due to the lowest mass gain and strong adhesion of the scale to the substrate, and Y-addition was effective in improving oxidation resistance because of its oxygen-scavenging effect in EPM processing. However, the overall oxidation process was dominantly controlled by the beneficial effect of the Mo-addition in the melted alloy due to the doping effect and formation of Mo-rich Al-depletion layer close to the substrate. The rolled alloy with the duplex microstructure greatly accelerated the oxidation rate because of a high volume fraction of alpha(2)-Ti3Al. At 900 degrees C, the melted alloy showed an excellent oxidation resistance during 350 h exposure. The oxidation rate and the spallation resistance of oxide scales did not depend strongly on the microstructure for the extruded or the rolled alloy. The poor spallation resistance of the oxide scales in the extruded alloy was probably related to thicker Mn-containing scales. Neither Mo-rich layer nor Y-rich zone in the oxide scales in the rolled alloy was observed at two exposure temperatures as a result of fast oxidation rate of the scale. (c) 2005 Elsevier Ltd. All rights reserved.
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The effect of Ti-addition on plastic deformation and fracture behavior of directionally solidified NiAl/Cr(Mo) eutectic alloys
K. Hagihara, Y. Sugino, Y. Umakoshi
INTERMETALLICS 14 ( 10-11 ) 1326 - 1331 2006年
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCI LTD
To improve the high-temperature strength of NiAl/Cr(Mo) eutectic alloys, the effect of Ti-addition on microstructure and mechanical properties was examined. Three directionally solidified (DS) alloys with the composition of Ni-(33 - x)Al-31Cr-3Mo-xTi (x = 0, 3 and 5 at.%, respectively), denoted 0Ti-, 3Ti- and 5Ti-alloys hereafter, were prepared. Temperature dependence of the yield stress and the room temperature fracture toughness of these DS alloys was examined. The aligned lamellae with B2-NiAl and A2-Cr(Mo) were formed in 0Ti-alloy, but the formation of lamellar structure was hindered by the Ti-addition. Cellular microstructures containing short plate shapes of Cr(Mo) phases were obtained in 3Ti- and 5Ti-alloys. In 5Ti-alloy, the precipitation of the L2(1)-Ni2AlTi was continued in NiAl matrix phase after the DS treatment. The Ti-addition induced a significant increase in high-temperature strength accompanied by a large deterioration of room temperature fracture toughness. The fracture toughness of 5Ti-alloy showed the low value of about 4 MPa m(1/2) because of the disturbance of microstructure. (C) 2006 Elsevier Ltd. All rights reserved.
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骨再建のための骨代替材料のナノ解析と骨質評価 査読あり
中野貴由, 萩原幸司, 馬越佑吉, 明石満, 中嶋英雄, 今里聡, 田畑泰彦
日本金属学会2006 年春期（第138 回）大会（2006.3.21－23. 東京） 2006年
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Microstructure and plastic deformation behavior of Ni-3(Ti,X) (X = Nb,Al) single crystals with long-period geometrically closely packed crystal structures 査読あり
K. Hagihara, T. Tanaka, H. Fujimoto, T. Nakano, Y. Umakoshi
INTERMETALLICS 14 ( 10-11 ) 1332 - 1338 2006年
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCI LTD
The crystal structure, phase stability and plastic deformation behavior of Ni-3(Ti1-xNbx) [x = 0, 0.01, 0.03, 0.05 or 0.10] and Ni3(Ti1-yAly) [y = 0.16 or 0.28] single crystals were investigated. The Substitution of Ti by Nb in Ni3Ti induced the formation of various long-period stacking ordered (LPSO) structures with 18-fold, 10-fold or 9-fold stacking sequences of closely packed plane (CPP) depending on the Nb content. In compression tests, the yield stress anomaly (YSA) appeared in ternary LPSO crystals as well as in binary Ni3Ti by slip on the CPP. The change in stacking sequence of CPP in the LPSO phases strongly affects the YSA behavior due to the change in APB energy on the non-closely packed plane. (C) 2006 Elsevier Ltd. All rights reserved.
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Temperature and orientation dependence of fracture behavior of directionally solidified duplex-phase crystals composed of Ni(3)X-type intermetallic compounds
Koji Hagihara, Naoyuki Yokotani, Yukichi Urnakoshi
ADVANCED STRUCTURAL AND FUNCTIONAL MATERIALS DESIGN, PROCEEDINGS 512 67 - 72 2006年
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：TRANS TECH PUBLICATIONS LTD
Fracture behaviors of three directionally solidified (DS) duplex-phase alloys composed of Ni(3)Nb(D0(a))/Ni(3)Al(Ll(2)), Ni(6)TaAl(D0(24))Ni(3)Al(L1(2)) and Ni(3)Ti(D0(24))/Ni(3)Si(L1(2)) phases, respectively were investigated by three-point bending tests, focusing on temperature and orientation dependence. The temperature-toughness relation showed dissimilar curves depending on alloy. The increasing rate of fracture toughness was the highest in the Ni(3)Al/Ni(3)Nb alloy with fine lamellar structure and was the lowest in the Ni(3)Al/Ni(6)TaAl alloy with rod-like precipitates. The controlling mechanism for the temperature dependence of fracture behavior of Ni(3)Al/Ni(3)Nb alloys was discussed.
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Plastic deformation behavior of NbSi2/MOSi2 crystals with oriented lamellae 査読あり
T. Nakano, K. Hagihara, Y. Nakai, Y. Umakoshi
INTERMETALLICS 14 ( 10-11 ) 1345 - 1350 2006年
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCI LTD
Plastic deformation behavior and dislocation microstructure were examined in two-phase silicides with oriented lamellae composed of the C40 (NbSi2) and C11b (MoSi2) phases. (Nb0.15Mo0.85)Si-2 single crystals with the C40 single phase were obtained by a floating zone method, and C11(b) plates precipitated from the C40 matrix during the subsequent annealing at 1400 degrees C satisfying the crystallographic orientation relationship of < <(1)over bar>2 (1) over bar0](C40)//[1 (1) over bar0](C11b) and (0001)(C40)//(110)(C11b). Temperature, annealing time and orientation dependences of plastic deformation behavior in the C40/C11(b) duplex crystals with the strict orientation relationship were examined in compression. Loading axes (phi) were selected to be 0 degrees and 45 degrees from [10 (1) over bar0] on [1 (1) over bar 10] zone in the C40 structure. Yield stress or fracture stress, for example, depended strongly on the angle between the loading axis and lamellar boundaries. The macro-yielding appeared at 1400 degrees C accompanied by the low yield stress around 300 MPa and an adequate plastic strain at phi = 45 degrees, while the crystals deformed at phi = 0 degrees failed just after high fracture stress around 900 MPa showing no plastic flow. This suggests that the deformation proceeds more easily parallel to the lamellar boundaries. In the constituent C11(b) phase, < 100] and 1/2<111] dislocations which are dominantly operative in binary MoSi2 at high temperatures were observed depending on the type of the C11(b) variant. Strain continuity at C11(b)/C11(b) or C11(b)/C40 boundaries was also discussed on the basis of continuity of Burgers vector of operative dislocations. (C) 2006 Elsevier Ltd. All rights reserved.
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GCP構造を有するD0_<24>型Ni_3Ti化合物の転位構造と異常強化挙動 査読あり
萩原 幸司, 中野 貴由, 馬越 佑吉
まてりあ : 日本金属学会会報 44 ( 12 ) 997 - 997 2005年12月
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GCP構造を有するDo24型Ni3Ti化合物の転位構造と異常強化挙動
萩原幸司, 中野貴由, 馬越佑吉
特集「電子顕微鏡法による材料開発のための微細構造研究最前線（5）」、まてりあ 2005年12月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Plastic deformation behavior of Ni3(Ti0.90Nb0.10) single crystals with nine-layered ordered rhombohedral structure 査読あり
K. Hagihara, T. Tanaka, T. Nakano, Y. Umakoshi
Acta Materialia 53 5051 - 5059 2005年10月
掲載種別：研究論文（学術雑誌）
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Improvement of cyclic oxidation resistance of Y-containing TiAl-based alloys with equiaxial gamma microstructures
Y Wu, K Hagihara, Y Umakoshi
INTERMETALLICS 13 ( 8 ) 879 - 884 2005年08月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCI LTD
The cyclic oxidation behavior of Y-containing TiAl-based alloys was studied by oxidation kinetic curves and microstructural modification of the scale. Oxidation resistance of the experimental alloys in synthetic air at 800 degrees C was improved by Y-addition. The Y-addition was very effective in improvement of the adhesion between scale and alloy due to decrease in thickness of the scale. Diffusion of oxygen and the growth of the oxide grains were strongly impeded by the precipitation of Y2O3 at oxide grain boundaries in the scale which was confirmed by the TEM observation. The excellent oxidation resistance obtained in the Y-containing alloys was mainly attributable to the formation of a continuous Al2O3 scale in the outer layer by retarding inward diffusion of oxygen. (c) 2005 Elsevier Ltd. All rights reserved.
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Crystal structure, phase stability and plastic deformation behavior of Ti-rich Ni-3(Ti,Nb) single crystals with various long-period ordered structures 査読あり
K Hagihara, T Tanaka, T Nakano, Y Umakoshi
Integrative and Interdisciplinary Aspects of Intermetallics 842 91 - 96 2005年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：MATERIALS RESEARCH SOCIETY
In Ni-Ti-Nb ternary system, there are some geometrically close-packed (GCP) phases with long-period stacking sequences of a close-packed plane (CPP). Among them, our focus is on the Ni-3(Ti0.90Nb0.10) crystals with Pb3Ba-type rhombohedral structure with nine-fold stacking sequence. Compression tests were conducted using the single crystals and the temperature and orientation dependences of plastic deformation behavior were investigated in comparison with those of D-024-Ni3Ti crystals with the four-fold stacking sequence. The K-W locking of screw dislocation was found to occur not only in the compounds such as Ni3Al and Ni3Ti with a relatively small unit cell, but also even in complex compounds with longer-period stacking structures by slip on the common CPP in the GCP structures.
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Deformation modes and anomalous strengthening of Ni3X-Type intermetallic compounds with the geometrically close-packed structure
Yukichi Umakoshi, Koji Hagihara, Takayoshi Nakano
Materials Science Forum 502 145 - 150 2005年
記述言語：英語 掲載種別：研究論文（学術雑誌）
Plastic deformation behavior including anomalous strengthening of Ni 3X-type compounds with D019, D03 and D0 24 structure were examined and summarized, focusing on the correlation between deformation characteristics and features of their crystal structures.
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Ni基GCP金属間化合物の積層構造と相安定性 査読あり
萩原 幸司, 田中 哲憲, 中野 貴由, 馬越 佑吉
まてりあ : 日本金属学会会報 43 ( 12 ) 993 - 993 2004年12月
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電子線照射誘起相変態を利用したナノ結晶・金属ガラス合金の創製
永瀬丈嗣, 中野貴由, 安田弘行, 萩原幸司, 馬越佑吉
大阪大学先導的研究オープンセンター 平成15年度年報, 2004, 44-47. 2004年10月
記述言語：日本語 掲載種別：研究論文（大学，研究機関等紀要）
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Influence of Y-addition on the Oxidation Behavior of Al-Rich γ-TiAl Alloys
Y.Wu, K.Hagihara, Y.Umakoshi
Intermetallics 12 ( 5 ) 519 - 532 2004年05月
記述言語：英語 掲載種別：研究論文（学術雑誌）
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Indentation fracture behavior of (Mo0.85Nb0.15)Si-2 crystals with C40 single-phase and MOSi2(C11(b))/NbSi2(C40) duplex-phase with oriented lamellae 査読あり
K Hagihara, S Maeda, T Nakano, Y Umakoshi
SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 5 ( 1-2 ) 11 - 17 2004年01月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：NATL INST MATERIALS SCIENCE
Fracture behavior and toughness of C40-structured (Mo0.85Nb0.15)Si-2 single crystals and MoSi2(C11(b))/NbSi2(C40) duplex-phase crystals with oriented lamellae were investigated by micro-Vickers hardness tests. The indentation fracture toughness in the C40 single-phase showed low values of about 1.0-1.4 MPa m(1/2), while fracture toughness was improved in the duplex-phase crystals. Ductile phase toughening by the C11(b) phase, deflection of crack-propagation at the lamellar boundary and the effect of residual stress field at the crack tip are considered to be responsible for the increment of fracture toughness of MoSi2(C11(b))/NbSi2(C40) duplex-phase crystals. (C) 2003 Elsevier Ltd. All rights reserved.
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Plastic deformation behavior of oriented Ni3Sn crystals with D019 structure 査読あり
K. Hagihara, T. Nakano, Y. Umakoshi
Scripta Materialia 48 577 - 581 2003年11月
掲載種別：研究論文（学術雑誌）
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Plastic deformation behaviour in Ni3Ti single crystals with D024?structure 査読あり
K. Hagihara, T. Nakano, Y. Umakoshi
Acta Materialia 51 2623 - 2637 2003年10月
掲載種別：研究論文（学術雑誌）
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Plastic deformation behavior and operative slip systems of ZrSi2 single crystals with C49 type of structure 査読あり
T Nakano, Y Omomoto, K Hagihara, Y Umakoshi
SCRIPTA MATERIALIA 48 ( 9 ) 1307 - 1312 2003年05月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
Plastic deformation behavior of ZrSi2 single crystals with C49 type of structure was investigated at temperatures up to 1500 degreesC in comparison with other silicides with C11(b), C40 and C54 types of structures. [100](010), [001](010), [101](010), and [001](100) slip systems were determined to operate and their CRSSs monotonously decreased with increasing temperature. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
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Plastic deformation behavior of Ni3X(X Nb, Ti, Sn) type HCP-based intermetallics with the geometrically close-packed structure 査読あり
K Hagihara, T Nakano, Y Umakoshi
DEFECT PROPERTIES AND RELATED PHENOMENA IN INTERMETALLIC ALLOYS 753 357 - 362 2003年
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：MATERIALS RESEARCH SOCIETY
In this paper, our recent results on the plastic deformation behaviors of Ni3X-type hcp-based GCP compounds, such as D0(a)-Ni3Nb, D0(19)-Ni3Sn and D0(24)-Ni3Ti, are summarized. The similarity and difference of their plastic behavior are discussed focusing on the correlation with the characteristic features of their crystal structures. The criterion for the occurrence of yield stress anomaly (YSA) by slip on the basal plane is also discussed.
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Slip systems, dislocation structure and plastic deformation behavior of Nl(3)Tl single crystals with D0(24) structure 査読あり
K Hagihara, T Nakano, Y Umakoshi
THERMEC'2003, PTS 1-5 426-4 1709 - 1714 2003年
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：TRANS TECH PUBLICATIONS LTD
The plastic deformation behavior of Ni3Ti single crystals with the D0(24) structure was investigated in this study. {1(1) over bar 00}<11(2) over bar 0 > prism slip and (0001)<2(11) over bar 0 > basal slip were operative in Ni3Ti. Anomalous strengthening of yield stress was observed for both slip systems. Especially, a remarkable yield stress anomaly (YSA) was found for the (0001) basal slip system over a wide temperature range between 300 and 800degreesC. The YSA was attributed to the Kear-Wilsdorf locking of 1/3<2(11) over bar 0 > screw dislocations from the (0001) slip plane onto the {01(1) over bar 0} planes.
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Microstructure and compressive flow stress of directionally solidified ternary Ni3(Al, Nb) and quaternary Ni3(Al, Nb, Ti) alloys with duplex phase 査読あり
K. Hagihara, T. Nakano, Y. Umakoshi
Science and Technology of Advanced Materials 3 193 - 199 2002年06月
掲載種別：研究論文（学術雑誌）
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Effect of Rh and V additions on plastic deformation behaviour in Ni3Nb single crystals with D0a structure 査読あり
Koji Hagihara, Takayoshi Nakano, Yukichi Umakoshi
Materials Transactions 43 ( 9 ) 2267 - 2274 2002年
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：Japan Institute of Metals (JIM)
The effect of Rh and V additions on phase stability and plastic deformation behaviour in Ni3Nb single crystals with the D0a structure was investigated, focusing on the slip behaviour of (010)[100], (010)[001] and (001)[100] systems in a wide temperature range between room temperature and 1200°C. The V addition induces no significant change in the critical resolved shear stress (CRSS) for (010)[100] slip at low temperatures, while the Rh addition is effective in increasing the CRSS at temperatures below 500°C and above 800°C, resulting in significant improvement of high-temperature strength. The increment of high-temperature strength is closely related to suppression of the climb motion of edge dislocations. The Rh addition also effectively increases the CRSS for (010)[001] and (001)[100] slip. The V addition was expected to enhance activation of the (010)[001] slip by reducing the SISF energy between the superpartials, but that was not achieved.
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Plastic deformation behavior by slip on (001)[100] in Ni3Nb single crystals with D0a structure 査読あり
K. Hagihara, T. Nakano, Y. Umakoshi
Materials Transactions 42 1998 - 2002 2001年10月
掲載種別：研究論文（学術雑誌）
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Operative slip systems and anomalous strengthening in Ni3Nb single crystals with the D0a structure 査読あり
Y. Umakoshi, K. Hagihara, T. Nakano
Intermetallics 9 ( 10-11 ) 955 - 961 2001年10月
記述言語：英語 掲載種別：研究論文（学術雑誌）
The plastic deformation behavior of Ni3Nb single crystals was examined in tension and compression to determine the operative slip and twinning systems, and to explore the anomalous strengthening behavior. A strong temperature dependence of the CRSS for both the slip and twinning systems was observed, which was dependent on the sample orientation. Anomalous flow behavior was also observed in Ni3Nb crystals deformed by (010)[100] and (001)[100] slip. The anomalous strengthening mechanism is discussed on the basis of both the anisotropy of APB energy and the formation of dragging atmosphere around moving dislocations. © 2001 Elsevier Science Ltd. All rights reserved.
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Cyclic deformation behavior of Ni3Nb single crystals deforming by slip on (010)[100] 査読あり
K. Hagihara, T. Nakano, Y. Umakoshi
Intermetallics 9 239 - 244 2001年08月
掲載種別：研究論文（学術雑誌）
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耐熱性Ni基金属間化合物単結晶の変形挙動
萩原 幸司, 中野 貴由, 馬越 佑吉
高温学会誌 27 ( 4 ) (22) 2001年07月
記述言語：日本語 掲載種別：研究論文（学術雑誌）
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Deformation twins in Ni3Nb single crystals with DOa structure 査読あり
K. Hagihara, T. Nakano, Y. Umakoshi
Mat. Res. Soc. Sympo. Proc., 646 N5.23.1 2001年03月
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス）
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Cyclic deformation behavior of Ni3Nb single crystals deforming by slip on (010)[100]
K Hagihara, T Nakano, Y Umakoshi
INTERMETALLICS 9 ( 3 ) 239 - 244 2001年03月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：ELSEVIER SCI LTD
Cyclic deformation behavior in Ni3Nb single crystals deforming by slip on (010)[100] was investigated. Fatigue tests were performed in a symmetrical push/pull mode at a fixed total strain amplitude (Delta epsilon) from +/-0.06 to +/-0.30% at ambient temperature. The cyclic hardening behavior varied below and above Delta epsilon = +/-0.15%. In the low strain amplitude group. the maximum stress amplitude reached a saturated value after initial strong hardening. while the cyclic hardening behavior in the high strain amplitude group were divided into three stages including the initial strong hardening. This initial strong hardening is related to the exhaustion hardening caused by the Kear-Wilsdorf locking. The hardening mechanism in each stage is discussed focusing on the cyclic stress-strain behavior, slip trace morphology and dislocation structure, (C) 2001 Elsevier Science Ltd. All rights reserved.
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D0_a型Ni_3Nb単結晶の変形微細組織
萩原 幸司, 中野 貴由, 馬越 佑吉
まてりあ : 日本金属学会会報 39 ( 12 ) 996 - 996 2000年12月
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Plastic deformation behaviour and operative slip systems in Ni3Nb single crystals 査読あり
K. Hagihara, T. Nakano, Y. Umakoshi
Acta Materialia 48 1469 - 1480 2000年05月
掲載種別：研究論文（学術雑誌）
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Plastic deformation behaviour and operative slip systems in Ni3Nb single crystals
K Hagihara, T Nakano, Y Umakoshi
ACTA MATERIALIA 48 ( 7 ) 1469 - 1480 2000年04月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
Temperature and orientation dependence of yield stress and operative slip system in Ni3Nb single crystals were examined. Four slip systems of (010)[100], (001)[100], {201}[10 (2) over bar] and (010)[001] and three twinning systems of {011}[0 (1) over bar 1], {211}[<(10)over bar> 7 13] and {012}[0 (2) over bar 1] were activated depending on the crystal orientation and tested temperature. Anomalous strengthening was observed for some orientations where (010)[100] or {201}[10 (2) over bar] slip was operative. A remarkable increase in the critical resolved shear stress (CRSS) for the (010)[100] slip occurred over a wide temperature range from -196 to 800 degrees C. The CRSS did not satisfy Schmid's law and the strain rate sensitivity of flow stress at a small plastic strain was negligible between room temperature and 700 degrees C where an anomalous stress increase occurred. The anomalous strengthening mechanism in Ni3Nb crystals deformed by [100] dislocations was discussed on the basis of anisotropy of APE energy on (010) and (001) in analogy with that in Ni3Al with the L1(2) structure. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.
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Strength and deformation mechanism of C40-based single crystal and polycrystalline silicides 査読あり
Y. Umakoshi, T. Nakano, K. Kishimoto, D. Furuta, K. Hagihara, M. Azuma
Materials Science and Engineering A 261 113 - 121 1999年10月
掲載種別：研究論文（学術雑誌）
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Plastic Deformation Behavior of Ni3Nb Single Crystals 査読あり
K. Hagihara, T. Nakano, Y. Umakoshi
Proceedings of MRS Symposium 552 KK10.7.1 1999年09月
記述言語：英語 掲載種別：研究論文（国際会議プロシーディングス）
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Plastic deformation behaviour of Ni<sub>3</sub>Nb single crystals
Koji Hagihara
MRS Sympo. Proc. : High temperature Ordered Intermetallics Alloys . 552 KK10.7.1 1999年
掲載種別：研究論文（学術雑誌）
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Mechanical properties of C40-based ternary Mo(Si,Al)2 and quaternary (Mo,Zr)(Si,Al)2 silicides 査読あり
K. Hagihara, T. Nakano, Y. Umakoshi
Scripta Materialia 38 471 - 476 1998年10月
掲載種別：研究論文（学術雑誌）
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Mechanical properties of C40-based ternary Mo(Si,Al)(2) and quaternary (Mo,Zr)(Si,Al)(2) silicides
K Hagihara, T Nakano, Y Umakoshi
SCRIPTA MATERIALIA 38 ( 3 ) 471 - 476 1998年01月
記述言語：英語 掲載種別：研究論文（学術雑誌） 出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD
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Stress anomaly in Al-rich Ti-Al single crystals deformed by the motion of 1/2〈110] ordinary dislocations 査読あり
T. Nakano, K. Hagihara, T. Seno, N. Sumida, M. Yamamoto, Y. Umakoshi
Philosophical Magazine Letters 78 ( 5 ) 385 - 391 1998年
記述言語：英語 掲載種別：研究論文（学術雑誌）
The microstructure and plastic deformation behaviour of Al-rich Ti-Al single crystals containing 54.7 and 58.0at.%Al have been examined, focusing on the effect of chemical ordering of a Al5Ti3superstructure on anomalous strengthening. Fine precipitates with the Al5Ti3 superstructure were developed in the L10matrix of the Ti-58.0 at. % Al alloy. The size and volume fraction of the precipitates varied depending on temperature. An anomalous increase in the yield stress of the two alloys appeared at around 800°C. This strengthening mechanism is discussed on the basis of the difference in antiphase-b oundary energies on (111), (110) and (001) planes in the Al5Ti3phase. © 1998 Taylor &
Francis Ltd.
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