論文 - 萩原 幸司
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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.
