FUKUMOTO Ken-ichi Institute of Materials Research, Tohoku University, Res. Associate, 金属材料研究所, 助手 (30261506)
YANO Shinzo Institute of Materials Research, Tohoku University, Res. Associate, 金属材料研究所, 助手 (60005915)
YAMAMOTO Takuya Institute of Materials Research, Tohoku University, Assistant Professor, 金属材料研究所, 講師 (50212296)
Self-healing property under particle irradiation is not uncommon to solid materials; many of the engineering materials keep their original shape even after several tens dpa, and this is exactly the result of self-healing property of the material. In this research, this intrinsic property, as well as extrinsic self-healing property given to these materials by adding precipitates, etc. is studied.
Firstly, vanadium alloys that have been known to exhibit swelling decrease after going over a peak swelling at some intermediate dpa value. Precipitates in these materials have been examined closely, identifying their nature by utilizing selected area diffraction taken with imaging plates, EDS and PEELS. It became clear that interface between these precipitates and the matrix act as trapping sites, where interface-catalyzed recombination occurs, and play an important role in suppressing swelling. However, this phenomenon only cannot explain the observed decrease in swelling while dpa increases m
onotonically. Increase in the precipitate density with dpa, caused by irradiation induced precipitation appears to be the mechanism explaining the decrease in swelling. Thus, it seems very important to give these precipitates good stability even after prolonged irradiation to high doses.
One of the good example of self-healing property demonstrated under high dpa irradiation is the one observed in V-5Ti alloy. In this experiment, the specimen was first irradiated up to 17dpa in FFTF/MOTA. The specimen was further irradiated in JMTR up to 0.1dpa, which is much smaller to the irradiation in FFTF. The microstructure after 17dpa in FFTF/MOTA was indistinguishable to those in the specimen irradiated to 0.1dpa in JMTR. The microstructure basically consisted of tiny TiO2 precipitates. This means that this microstructure had been saturated below 0.1dpa and did not evolve even during the prolonged irradiation up to 17dpa. This observation is the result of remarkable self-healing mechanism due to the microstructure consisting of fine precipitates; the interface between the matrix and the precipitates act as catalysis for mutual recombination between self-interstitial atoms and vacancies.
Computer code based on chemical rate theory has been developed in order to analyze the self-healing property observed experimentally. The input parameters have been obtained by using HVEM in situ irradiation technique. The result of the simulation was in good qualitative agreement while quantitative agreement was fair. The reason for this insufficient agreement between the theory and the experiment may partly be because of the insufficient approximation adopted in the theory. It is believed other mechanism is responsible for this and will be the topic of further research. Less