TOKUNAGA Toko

写真a

Affiliation Department etc.

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

Title

Assistant Professor

Graduating School

  • 2013.04
    -
    2015.06

    Hokkaido University   Graduate School of Engineering,   Graduated

  • 2011.04
    -
    2013.03

    Hokkaido University   Graduate School of Engineering   Graduated

  • 2007.04
    -
    2011.03

    Hokkaido University   Faculty of Engineering   Graduated

 

Papers

  • 青森県量子科学センターにおけるBNCT

    Toko Tokunaga, Shingo Hachinohe, Hiroyoshi Kikuchi, Toyomi Baba

      36 ( 2 ) 62 - 63   2021.02

    Research paper (scientific journal)   Multiple Authorship

  • Development of High Corrosion- and Wear-Resistant Al-Si Alloy Coating on AZ80 Mg Alloy by Hot Extrusion

    Toko Tokunaga, Kazushi Sotomoto, Munekazu Ohno, Kiyotaka Matsuura

    Journal of Materials Engineering and Performance   29   6355 - 6362   2020  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • Microstructure refinement and mechanical properties improvement of Al-Si-Fe alloys by hot extrusion using a specially designed high-strain die

    酒向志乃, 徳永透子, 大野宗一, 松浦清隆

    Journal of Materials Processing Technology   277 ( 116447 ) 1 - 9   2020  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • Enhancement of ductility for Al–Si–Fe alloy by refining β phase with a novel ball-die extrusion

    徳永透子, 犬伏晴紀

    SN Applied Sciences   1 ( 10 ) 1334   2019.10  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • Microstructure evolution during superplastic deformation of an Al-coated Mg alloy sheet

    T. Tokunaga, M. Ohno

    Journal of Alloys and Compounds   805   436 - 443   2019  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • Fabrication of Al-Coated Mg-Li Alloy Sheet and Investigation of Its Properties

    T. L. Zhang, T. Tokunaga, M. Ohno, M. L. Zhang, K. Matsuurah

    Acta Metallurgica Sinica (English Letters)   32   169 - 177   2019  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • Coating on magnesium alloy with super duralumin by hot extrusion and evaluation of its surface properties

    Toko Tokunaga, Kazushi Sotomoto, Munekazu Ohno, Kiyotaka Matsuura

    Materials Transactions ( Japan Institute of Metals (JIM) )  59 ( 3 ) 432 - 436   2018  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    The poor corrosion resistance of Mg alloys, which is well known as one of the lightest structural metal materials, limits a wide use of these alloys. In order to dramatically increase not only the corrosion resistance but also the surface hardness of Mg alloys (AZ80), coating with A2024 Al alloy by hot extrusion has been attempted in this study. The coating was successfully realized by hot extrusion of a Mg alloy (AZ80) billet together with an Al alloy plate placed between the billet and the extrusion die. The A2024 Al alloy-coated Mg alloy exhibited an excellent corrosion resistance and no weight loss was observed after immersion in a 5 mass% HCl aqueous solution for 10 min while a weight loss of about 1500 g・m−2 was observed in case of AZ80 Mg alloy without coating under the same condition. The surface hardness of the coated alloy was increased to about 85 HV by aging for 144 h at room temperature after solution treatment for 3 h at 673 K.

  • Brazed Bonding between SiAlON and heat-resistant alloys with application of filler materials

    Toko Tokunaga, Masayuki Koshiyama, Kazuya Kurokawa, Munekazu Ohno, Kiyotaka Matsuura

    Materials Transactions ( Japan Institute of Metals (JIM) )  59 ( 6 ) 969 - 975   2018  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    It has been required to improve the heat efficiency of thermal power generation system for the sake of mitigation of the global warming and resource depletion problems. For improving the heat efficiency, it is effective to increase the steam temperature, and as a result, appropriate heatresistant alloys are needed. Although SUS304 stainless steel and Ni-based superalloys have been proposed as promising heat-resistant alloys until now, there still remain some concerns such as high-temperature corrosion by flaming gas and erosion by combustion ash. Thus, the present authors propose SiAlON ceramic coating on SUS304 and INCONEL X-750 because SiAlON has excellent heat, wear and corrosion resistances. In the present study, brazed bonding between SiAlON and these heat-resistant alloys was attempted with the applications of Cu and Ag as a soft filler material to reduce the residual stress generated due to the difference in thermal expansion coefficient between SiAlON and the heat-resistant alloys. As for the bonding with the Cu filler, the SiAlON/Cu/SUS joint was successful when the brazing time was short. However, when the brazing time was long (for example, 60 minutes), Fe-based grains were formed in the Cu filler layer, and the cracks were formed in the SiAlON near the joint interface during cooling in the brazing process. It was considered that the Cu filler was hardened by the formation of the Fe-based grains and could not reduce the residual stress. As for the bonding with the Ag filler, on the other hand, the SiAlON/Ag/SUS joint was successful even for a long brazing time. The SiAlON/Ag/INCONEL joint was also successful. The bending strengths of these SiAlON/Cu/SUS, SiAlON/Ag/SUS and SiAlON/Ag/INCONEL joints were evaluated by a three point bending test, and the results were approximately 200, 270 and 350 MPa, respectively. In all cases fracture occurred in the SiAlON, which means that the SiAlON and the alloys were strongly bonded.

  • Low temperature superplasticity of a dual-phase Mg-Li-Zn alloy processed by a multi-mode deformation process

    T. L. Zhang, T. Tokunaga, M. Ohno, R. Z. Wu, M. L. Zhang

    Materials Science & Engineering A   737   61 - 68   2018  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

  • Fabrication of unidirectionally orientated carbon fiber reinforced cu-based composites by hot extrusion and evaluation of their thermal properties

    Hiroto Kontani, Toko Tokunaga, Munekazu Ohno, Katsuhiko Sasaki, Kiyotaka Matsuura

    Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals ( Japan Institute of Metals (JIM) )  82 ( 5 ) 125 - 129   2018  [Refereed]

    Research paper (scientific journal)   Multiple Authorship

    Unidirectional orientation of the carbon fiber is essential in the fabrication of Cucarbon fiber composites with high thermal conductivity, because the fiber exhibits its very high thermal conductivity only in the longitudinal direction. In this study, hot extrusion of a mixture of Cu powder and carbon fiber was applied to fabricate the unidirectionally orientated carbon fiber reinforced Cubased composite and the effects of the volume fraction of carbon fiber on the thermal conductivity have been investigated. It has been demonstrated that hot extrusion of the Cu powdercarbon fiber mixture successfully align the fiber to orient along the extrusion direction, and consequently, the thermal conductivity in this direction increases with the volume fraction of carbon fiber. For the composite with more than 30 vol% carbon fiber, the application of ultrasonic vibration treatment to the powderfiber mixture is effective for improving the homogeneity of the mixing and hence increasing the relative density and the thermal conductivity of the composite.

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Presentations

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