論文 - 萩原 幸司
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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）
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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
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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）
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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
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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）
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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）
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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.
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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）
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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）
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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.
