HAGIHARA Koji

写真a

Affiliation Department etc.

Department of Physical Science and Engineering
Department of Physical Science and Engineering

Title

Professor

Mail Address

E-mail address

Graduating School

  •  
    -
    2002

    Osaka University     Graduated

  •  
    -
    1997

    Osaka University   Faculty of Engineering   Graduated

Graduate School

  •  
    -
    2002

    Osaka University  Graduate School, Division of Engineering  Doctor's Course  Completed

  •  
    -
    1997

    Osaka University  School of Engineering  Doctor's Course  Completed

External Career

  • 2021.07
    -
    Now

      Professor  

  • 2021.04
    -
    2021.06

    Osaka University   Graduate School of Engineering   Professor  

Academic Society Affiliations

  •  
     
     

    THE JAPAN SOCIETY OF MECHANICAL ENGINEERS

  •  
     
     

    THE JAPAN INSTITUTE OF LIGHT METALS

  •  
     
     

    THE JAPANESE SOCIETY FOR BIOMATERIALS

 

Papers

  • Comparison of microstructure, crystallographic texture, and mechanical properties in Ti–15Mo–5Zr–3Al alloys fabricated via electron and laser beam powder bed fusion technologies

    S.-H. Sun, K. Hagihara, T. Ishimoto, R. Suganuma, Y.-F. Xue, T. Nakano

    Additive Manufacturing ( Elsevier BV )  47   102329   2021.10  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    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.

  • Quantitative estimation of kink-band strengthening in an Mg–Zn–Y single crystal with LPSO nanoplates

    K. Hagihara, R. Ueyama, T. Tokunaga, M. Yamasaki, Y. Kawamura, T. Nakano

    Materials Research Letters ( Taylor and Francis )  9   467 - 474   2021.09  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    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.

  • Control of kink-band formation in mille-feuille structured Al/Al2Cu eutectic alloys

    K. Hagihara, T. Tokunaga, K. Nishiura, S. Uemichi, S. Ohsawa

    Materials Science & Engineering A ( Elsevier BV )  825   141849   2021.08  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    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.

  • Intrinsic kink bands strengthening induced by several wrought-processes in Mg-Y-Zn alloys containing LPSO phase

    H. Somekawa, D. Ando, K. Hagihara, M. Yamasaki, Y. Kawamura

    Materials Characterization ( Elsevier BV )  825   141849   2021.08  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    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.

  • Factor which governs the feature of texture developed during additive manufacturing; clarified from the study on hexagonal C40-NbSi2

    K. Hagihara, T. Ishimoto, M. Suzuki, R. Ozasa, A. Matsugaki, P. Wang, T. Nakano

    Scripta materialia ( Elsevier BV )  203   114111   2021.07  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    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.

  • Ultrahigh specific strength in a magnesium alloy strengthened by spinodal decomposition

    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 ( American Association for the Advancement of Science (AAAS) )  7 ( 23 ) eabf3039 - eabf3039   2021.06  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    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.

  • Formation of <0001>-rotation-type kink boundary in Mg–Zn–Y alloy with long-period stacking ordered structure

    Michiaki Yamasaki, Tsuyoshi Mayama, Tsubasa Matsumoto, Koji Hagihara, Daria Drozdenko, Yoshihito Kawamura

    Materials Science and Engineering: A ( Elsevier BV )  819   141466 - 141466   2021.05  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • Stability of crystallographic texture in laser powder bed fusion: Understanding the competition of crystal growth using a single crystalline seed

    Takuya Ishimoto, Koji Hagihara, Kenta Hisamoto, Takayoshi Nakano

    Additive Manufacturing ( Elsevier BV )  43   102004 - 102004   2021.05  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • Kink-band formation in directionally solidified Mg/Mg2Yb and Mg/Mg2Ca eutectic alloys with Mg/Laves-phase lamellar microstructure

    Koji Hagihara, Kosuke Miyoshi

    Journal of Magnesium and Alloys ( Elsevier BV )  in press   2021.04  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • Surprising increase in yield stress of Mg single crystal using long-period stacking ordered nanoplates

    Koji Hagihara, Ryohei Ueyama, Michiaki Yamasaki, Yoshihito Kawamura, Takayoshi Nakano

    Acta Materialia ( Elsevier BV )  209 - 116797   2021.04  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

display all >>

 
 

Academic Activity

  • 2021.07
    -
    Now

    THE JAPAN INSTITUTE OF LIGHT METALS  

  • 2019.03
    -
    Now

    THE JAPAN INSTITUTE OF LIGHT METALS  

  • 2017.04
    -
    2019.03

    THE JAPAN INSTITUTE OF LIGHT METALS  

  • 2015.04
    -
    2021.03

    THE JAPAN INSTITUTE OF LIGHT METALS