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平成28年6月20日(月) 会場: 原子炉工学研究所 北2号館6階会議室

発表者氏名 指導教員 論  文  題  目

Mohd Idzat Idris

小原 徹
Recovery behavior of neutron- irradiation-induced defects in monolithic SiC and SiCf/SiC composites
 Silicon carbide (SiC) has been used extensively in nuclear applications due to its excellent mechanical and thermal properties. However, its inherent brittle nature could lead a high probability of catastrophic failure under excess loads. Hence, to ensure a sufficient strength and reliability in severe neutron environments, the proposed materials for future structural parts is a continuous silicon carbide fiber-reinforced silicon carbide matrix (SiCf/SiC) composites. It has been recognized as a key material for high temperature gas turbine, aerospace industries and future nuclear power applications. In fusion power application, SiCf/SiC composites have been expected to be used as the components for fusion breeding blanket and divertor.
 In this study, several types of SiC and SiCf/SiC composites have been neutron-irradiated simultaneously at moderate fluence 2.0-2.5×1024 n/m2 (E>0.1 MeV) with low irradiation temperature (333-363 K) for 60 days. Radiation effects on those specimens was investigated in order to understand the fundamental responses by SiC and SiCf/SiC composites. In addition, recovery behavior of monolithic high purity SiC and SiC with sintering additives have been conducted to examine the recombination mechanism and the defects stability by post-irradiation annealing up to 1673 K. Finally, microstructures of the specimens have been observed using transmission electron microscopy (TEM) to clarify type of defects on SiC after neutron irradiation.
   Results showed that irradiated high purity SiC was swelled approximately 1.1% attributed to the point defects, while length change of impurity SiC was 0.1% larger than those of the high purity SiC owing to the presence of large amount of sintering additives. Further, SiCf/SiC composites were less swelled than those monolithic SiC due to the reinforcement of fibers. Investigation on the recovery behavior showed that high purity SiC and SiC with 12% of sintering additives have recovered completely except SiC with 18% of sintering additives. However, they have similar recovery mechanism, where interstitial atoms and vacancies were recombined each other after the heat treatment. Observations of the microstructures of irradiated SiC clarified that most of the defects are point defects and no dislocation loop has been perceived. Furthermore, tiny black spots have been seen on annealed specimens, where remaining interstitials that not annihilate during post-irradiation annealing could coagulated and form small interstitial clusters.