| 研究実績の概要 |
Oxide dispersion strengthened (ODS) steels are considered as the advanced structural materials of fusion blanket and nuclear fuel cladding tube in fast breeder reactors due to their excellent tensile and creep strength and good irradiation resistance. In this work, the long-term creep properties and fracture mechanism were investigated to determine the maximum operation temperature of materials. Also, irradiation experiments by electron and ion were carried out to reveal the microstructural evolution especially the stability of nano-particles.
The creep test was carried out at the temperature of 773 to 973 K, the stress level of 120-600 MPa, and creep rate of 1E-6 - 1E-10/s. 12Cr-ODS steel exhibited excellent and unique behaviors, such as significantly longer second steady-state stage, smaller in minimum creep rate, and almost absence of tertiary accelerated creep stage. The creep stress exponent n was in the range of 10-50, which is much higher than the heat-resistant steels. The existence of a creep threshold stress, which associated with the interaction between dislocations and nano-scale oxide particles, is expected. SEM/EBSD observations showed a mixed ductile and brittle fracture mode. High density of defects and/or cavities, were formed along rolling direction or grain elongated direction and perpendicular to the tensile direction, and connected into cracks. The electron irradiation was performed at temperature ranging from 673 to 873 K and with the energy from 0.75 to 2 MeV, as well as ion irradiation, showed that nano-particles were unstable under irradiation.
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| 今後の研究の推進方策 |
The remained creep property testing at lower testing temperatures, and long-term aging in 12Cr-ODS will be finished. The corresponding microstructural evolution, including the fractography, during will be analyzed by SEM, EBSD and TEM. The expected fracture model is evolution of grain and grain boundaries, precipitates and dislocation during the creep process. The creep deformation and fracture maps will be built for the prediction of the creep mechanisms at related temperature and stress condition. The longer-term creep performance in the typical fusion blanket limit condition and fission reactor will be predicted, which can provide the important reference for the design of advanced nuclear reactors. In-situ observation of the stability of nano-particles during the electron irradiation, as well as ion irradiation, will be continued to reveal microstructural evolution under irradiation.
Finally, all the experimental results will be summarized and a series of research reports will be completed. These results will be presented in domestic conference and 17th International Conference on Fusion Reactor Materials (ICFRM-17). Manuscripts will be prepared and expected to be published in scientific journals.
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