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ABSTRACT
Hokkaido University has installed multi-beam irradiation facility combining with atomic resolution high voltage electron microscope and ion-accelerators. By using the facility several groups have used for in-situ observation of damage structure in fusion and fission reactor materials and systhesization of non-stoichiometric phases. At this time an example of in-situ observation for radiation-damage in fusion and fission reactor materials will be introduced during an electron-helium ion irradiation.
Ferritic/martensitic steels are candidate materials for fusion reactors, however, there are main materials issues such as irradiation embrittlement and elevation in ductile-brittle transition temperature. Now days, migration energy of point defects influence evolution of irradiation-induced dislocation loops, and hydrogen and/or helium created by nuclear transmutation reaction are becoming important terms in “Multi-scale modeling” applying for solving such macroscopic materials behavior.
In order to investigate the effect of helium on migration energy of vacancies or interstitials in Fe-Cr model alloys, two types of irradiations, electron single irradiation and electron-helium dual irradiation and their in situ observations were performed at 300 - 500 ℃. The acceleration voltage of electron in a HVEM was 1250 kV, and He ion was 100 kV. The damage rate was 10x10-4 dpa/s, and the injection rate was 10 He ppm/dpa.
At the beginning of the electron-irradiation interstitial-type dislocation loops were nucleated and then grew on <001> and <111>. In the case of dual-beam irradiation, the loops were nucleated with much higher number density, and the grown with continuing irradiation. By using simple method based on Kiritani and Yoshida [3], the migration energy of interstitials was evaluated as 0.2 eV in both types of irradiations, and that of vacancies was evaluated as 0.95 eV in electron-irradiation and 1.5 eV in dual beam irradiation, where the difference of two energies, 0.5 eV, could be assumed to be net binding energy of vacancy and helium atom. These results are reasonable comparing to the results from other materials
References
K. Oka, S. Ohnuki, S. Yamashita, N. Akasaka, H. Tanigawa, Mater. Trans., 48 (2007)2563-2566
S. Watanabe, Mater. Sci. Forum，561-565 (2007) 2021
M. Kiritani et al., J. Phys. Japan, 38 (1975)
H. Seto, N. Hashimoto, H. Kinoshita, S. Ohnuki, Effects of multi-beam irradiation on defect formation in Fe-Cr alloys, Journal of Nuclear Materials in press (2011)
Biography:
SomeiOhnuki
Professor
Laboratory of Advanced Materials
Materials Science Division
GraduateSchool of Engineering
HokkaidoUniversity (NationalUniversity)
Japan
Educational Background:
Hokkaido Univ. Faculty of Engineering, Department of Metallurgy, Bachelor degree, 1975
HokkaidoUniv. Graduate School of Engineering, Material Science Course, Master degree, 1977
Doctor of Engineering; 1980
Working history
Special Researcher, Japanese Society of Promotion of Science, 1980
Assistant Professor: HokkaidoUniv., Faculty of Engineering, Laboratory of High Voltage Electron Microscopy, 1981
Associate professor: Hokkaido Univ. Faculty of Engineering, Material Science Laboratory, 1988
Visiting Researcher: Pacific Northwest National Laboratory, Richland, WA, USA, 1988-1989
Professor: HokkaidoUniv.GraduateSchool of Engineering Materials Science Division, 1996
Research Fields:
Materials Science, High Voltage Electron Microscopy, Radiation Damage, Hydrogen Related Materials |
