研究者詳細 - 萩原　幸司

論文 - 萩原　幸司

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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/

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

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Informa UK Limited

DOI： 10.1080/14686996.2022.2137696

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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）

DOI： https://doi.org/10.1016/j.ijplas.2022.103419

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）

DOI： https://doi.org/10.1016/j.ijplas.2022.103294

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

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）

DOI： 10.1007/s11837-021-04966-7

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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

DOI： 10.1016/j.jmst.2021.07.058

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.

DOI： 10.1016/j.addma.2021.102329

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.

DOI： 10.1080/21663831.2021.1974593

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.

DOI： 10.1016/j.msea.2021.141849

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.

DOI： 10.1016/j.matchar.2021.111348

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.

DOI： 10.1016/j.scriptamat.2021.114111

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.

DOI： 10.1126/sciadv.abf3039

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

DOI： 10.1016/j.addma.2021.102004

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

DOI： 10.1016/j.msea.2021.141466

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

DOI： 10.1016/j.actamat.2021.116797

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

DOI： 10.1016/j.jma.2021.02.006

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.

DOI： 10.1016/j.wear.2021.203758

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

DOI： 10.1016/j.msea.2020.140087

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

DOI： 10.1016/j.intermet.2020.106881

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