Papers - HAGIHARA Koji
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Plastic deformation mechanisms of biomedical Co-Cr-Mo alloy single crystals with hexagonal close-packed structure Reviewed
Wataru Kaita, Koji Hagihara, Luis Augusto Rocha, Takayoshi Nakano
SCRIPTA MATERIALIA 142 111 - 115 2018.01
Language：English Publishing type：Research paper (scientific journal) Publisher：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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Strengthening mechanisms acting in the extruded Mg-based LPSO phase
HAGIHARA Koji, YAMASAKI Michiaki, KAWAMURA Yoshihito, NAKANO Takayoshi
The Proceedings of the Materials and Mechanics Conference 2018 ( 0 ) 2018
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers
<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 beta-type Ti-Nb-Ta-Zr-alloy single crystals developed for the single-crystalline implant Reviewed
Koji Hagihara, Takayoshi Nakano
INTERNATIONAL JOURNAL OF PLASTICITY 98 27 - 44 2017.11
Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD
Quaternary Ti-Nb-Ta-Zr (TNTZ) type beta-Ti alloys with a body-centered cubic (bcc) structure have been of great interest as new implant biomaterials for bone replacement. Recently, we have proposed a "single crystalline beta-Ti implant" as a novel hard-tissue replacement to suppress the stress shielding to bone after healing. To develop this, the fatigue properties and its controlling mechanisms of the TNTZ single crystals must be clarified. In this study, we focused on three alloys: Ti-25Nb-10Ta-5Zr(25Nb), Ti-29Nb -13Ta-4.6Zr(29Nb), and Ti-35Nb-10Ta-5Zr(35Nb) (mass%), and the cyclic deformation behaviors were examined using their single crystals. The shapes of the hysteresis loops were significantly different for these alloys, which was ascribed to the operation of different deformation modes: stress-induced alpha"-martensite (alpha"-SIM), {332}< 113 > twinning, and {101}< 111 > slip in the 25Nb, 29Nb, and 35Nb alloys, respectively. The hysteresis loops during cyclic deformation exhibited very irregular shapes for 25Nb and 29Nb, accompanied by a flow-stress asymmetry in tension and compression. This was caused by the polarized feature on the formation of them in tension and compression. In addition, the apparent yield stress in a hysteresis loop greatly decreased after the second cycle, owing to the reversible motion of the interfaces of the SIM and {332} twins by altering the direction of the applied stress. Although the cyclic deformation behavior was controlled by a similar mechanism in them, 29Nb was found to exhibit a much shorter fatigue life than 25Nb. This is because of the difference in the decreasing tendency of the reversibility for the SIM and {332} twins as cyclic deformation proceeded. The obtained results demonstrate that the controls of their asymmetric features and the reversible motion are the important factors to develop these alloys as a practical "single crystalline beta-Ti implant". (C) 2017 The Authors. Published by Elsevier Ltd.
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1400℃でも使用可能な超高温耐熱材料を開発 International journal
萩原幸司, 中野貴由
Ceramics Japan 52 724 2017.09
Language：Japanese Publishing type：Research paper (scientific journal)
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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 Reviewed
萩原幸司
軽金属 67 293 - 300 2017.08
Language：Japanese Publishing type：Research paper (scientific journal)
DOI： 10.2464/jilm.67.293
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Unusual dynamic precipitation softening induced by dislocation glide in biomedical beta-titanium alloys Reviewed
K. Hagihara, T. Nakano, M. Todai
Scientific Reports 7 8056 2017.07
Language：English Publishing type：Research paper (scientific journal)
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Control of morphological and microstructural anisotropy through powder-based metal additive manufacturing Reviewed
Takayoshi Nakano, Takuya Ishimoto, Koji Hagihara
Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy 64 ( 6 ) 259 - 264 2017.06
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of the Japan Society of Powder and Powder Metallurgy
The utilization of "anisotropy" is becoming an important direction for realizing highly-functionalized products overcoming the current functional limits for materials with isotropic properties. In particular for the use in aerospace and biomedical industries, some products are exposed to anisotropic stress fields. Therefore, the products should be anisotropic along the functional axis. Additive manufacturing (AM) technology was originally specialized to fabricate the complicated structures in an arbitrary way. However, when it comes to metal AM, the control of material anisotropy has received an increasing attention in recent years. In this review article, the latest findings regarding the control of mechanical anisotropy through the modifications of macroscopic porous structure, microstructure, and crystallographic orientation by powder-based metal AM technologies are introduced. The powder-based metal AM is able to control a wide range of anisotropy from crystallographic texture to pore structure, however, their simultaneous control is yet challenging. Attainment of this heightens the value of metal AM technology and enhances the AM products' functions.
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 Reviewed
K. Hagihara, T. Ikenishi, H. Araki, T. Nakano
Scientific Reports 7 3936 2017.05
Language：English Publishing type：Research paper (scientific journal)
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Crystallographic texture control of beta-type Ti-15Mo-5Zr-3Al alloy by selective laser melting for the development of novel implants with a biocompatible low Young's modulus Reviewed
Takuya Ishimoto, Koji Hagihara, Kenta Hisamoto, Shi-Hai Sun, Takayoshi Nakano
SCRIPTA MATERIALIA 132 34 - 38 2017.04
Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD
We first successfully achieved the two types of distinct texture control in low-modulus beta-type Ti-15Mo-5Zr3-Al alloy products using selective laser melting. Bidirectional scanning with and without a rotation of 90 between the layers gave rise to different textures with preferential orientations of "001" and "011" along the building direction, respectively. Control of the growth behavior of the columnar cells in the melt pools via scanning strategies enabled the generation of such different textures. The obtained material exhibits a low Young's modulus of 68.7 +/- 0.9 GPa, which potentially allows for the development of implants that can suppress stress shielding. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd.
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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 Reviewed
Koji Hagihara, Takaaki Ikenishi, Takayoshi Nakano
SCRIPTA MATERIALIA 131 19 - 23 2017.04
Language：English Publishing type：Research paper (scientific journal) Publisher：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 Reviewed
K. Kimura, K. Hayashi, K. Hagihara, H. Izuno, N. Happo, S. Hosokawa, M. Suzuki, H. Tajiri
Materials Transactions 58 539 - 542 2017.03
Language：English Publishing type：Research paper (scientific journal)
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Successful additive manufacturing of MoSi2 including crystallographic texture and shape control Reviewed
Koji Hagihara, Takayoshi Nakano, Masahiro Suzuki, Takuya Ishimoto, Suyalatu, Shi-Hai Sun
JOURNAL OF ALLOYS AND COMPOUNDS 696 ( 696 ) 67 - 72 2017.03
Language：English Publishing type：Research paper (scientific journal) Publisher：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 Reviewed
Mitsuharu Todai, Takayoshi Nakano, Tianqi Liu, Hiroyuki Y. Yasuda, Koji Hagihara, Ken Cho, Minoru Ueda, Masao Takeyama
Additive Manufacturing 13 61 - 70 2017.01
Language：English Publishing type：Research paper (scientific journal) Publisher：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 Reviewed
Koji Hagihara, Takayoshi Nakano, Keita Sasaki
SCRIPTA MATERIALIA 123 149 - 153 2016.10
Language：English Publishing type：Research paper (scientific journal) Publisher：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 Reviewed
K. Hagihara, T. Okamoto, H. Izuno, M. Yamasaki, M. Matsushita, T. Nakano, Y. Kawamura
Proceedings of PRICM9 27 - 31 2016.08
Language：English Publishing type：Research paper (international conference proceedings)
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Effect of additional elements on fracture toughness of (Mo0.85Nb0.15)Si-2 C40/C11(b) lamellar-structured crystals Reviewed
Koji Hagihara, Koretaka Yuge, Takaaki Ikenishi, Haruka Araki, Takayoshi Nakano
MATERIALS LETTERS 177 99 - 103 2016.08
Language：English Publishing type：Research paper (scientific journal) Publisher：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 Reviewed
Koji Hagihara, Masayoshi Okubo, Michiaki Yamasaki, Takayoshi Nakano
CORROSION SCIENCE 109 68 - 85 2016.08
Language：English Publishing type：Research paper (scientific journal) Publisher：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 beta-type Ti-29Nb-13Ta-4.6Zr alloy single crystals for the development of single crystalline beta-Ti implants Reviewed
Koji Hagihara, Takayoshi Nakano, Hideaki Maki, Yukichi Umakoshi, Mitsuo Niinomi
SCIENTIFIC REPORTS 6 20779 2016.07
Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP
beta-type Ti-29Nb-13Ta-4.6Zr alloy is a promising novel material for biomedical applications. We have proposed a 'single crystalline beta-Ti implant' as new hard tissue replacements for suppressing the stress shielding by achieving a drastic reduction in the Young's modulus. To develop this, the orientation dependence of the plastic deformation behavior of the Ti-29Nb-13Ta-4.6Zr single crystal was first clarified. Dislocation slip with a Burgers vector parallel to < 111 > was the predominant deformation mode in the wide loading orientation. The orientation dependence of the yield stress due to < 111 > dislocations was small, in contrast to other beta-Ti alloys. In addition, {332} twin was found to be operative at the loading orientation around [001]. The asymmetric features of the {332} twin formation depending on the loading orientation could be roughly anticipated by their Schmid factors. However, the critical resolved shear stress for the {332} twins appeared to show orientation dependence. The simultaneous operation of < 111 > slip and {332} twin were found to be the origin of the good mechanical properties with excellent strength and ductility. It was clarified that the Ti-29Nb-13Ta-4.6Zr alloy single crystal shows the "plastically almost-isotropic and elastically highly-anisotropic" nature, that is desirable for the development of 'single crystalline beta-Ti implant'.
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 Reviewed
萩原幸司, 森川龍哉, 東田賢二
金属 （雑誌） 86 472 - 479 2016.06
Language：Japanese Publishing type：Research paper (scientific journal)
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Plastic deformation behavior of 10H-type synchronized LPSO phase in a Mg-Zn-Y system Reviewed
Koji Hagihara, Takuya Okamoto, Hitoshi Izuno, Michiaki Yamasaki, Masafumi Matsushita, Takayoshi Nakano, Yoshihito Kawamura
ACTA MATERIALIA 109 90 - 102 2016.05
Language：English Publishing type：Research paper (scientific journal) Publisher：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.
