論文 - 萩原 幸司
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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.
