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高温・重照射した酸化物分散強化型鋼中の複合酸化物粒子と転位の相互作用

Interaction among dislocation and complex oxide particles in ODS steels haevily-irradiated at high temperature

山下 真一郎  ; 赤坂 尚昭; 小野瀬 庄二 

Yamashita, Shinichiro; Akasaka, Naoaki; Onose, Shoji

酸化物分散強化型(MA957)合金中の酸化物粒子の照射下相安定性や転位との相互作用を把握し、次世代原子炉材料の設計に反映することを目的とし、高速実験炉「常陽」で中性子照射したMA957の微細組織観察を行った。観察の結果、982Kで100dpa程度中性子照射した場合においても、微細な粒子が転位と相互作用し、転位のピン止めに寄与していることが明らかとなった。また、微細粒子の元素分析からは、この粒子がチタンとイットリウムを含んでおり、チタンの適量添加により微細化した複合酸化物粒子である可能性が高いことが示された。

Oxide Dispersion Strengthened (ODS) ferritic steel dealt with this study was a MA957 (Fe-0.015C-14Cr-0.3Mo-1.0Ti-0.25Y2O3). The objectives of this study were to understand oxide particle stability of ODS steel during irradiation and interaction among dislocation and oxide particles, reflecting to advanced nuclear reactor design of next generation. Development of some nuclear energy generating systems has been proposed and supported intensively under several international collaboration programs (Generation IV International Forum (GIF), Advanced Fuel Cycle Initiative (AFCI), International Nuclear Energy Research Initiative (I-NERI) etc).Current research issue on ODS ferritic steels is considered to be poverty of experience and understanding on their practical neutron-irradiation behaviors at the temperature higher than 600C.In this research, a MA957, most familiar but primitive 14CrODS ferritic steel contained the highly textured-anisotropic grain structures, was irradiated at 500-700$$^{circ}$$C to fast fluences ranging from 19.8 to 20.8 $$times$$ 1026 n/m2 (E $$>$$ 0.1MeV) in the experimental fast reactor JOYO. The dose achieved varied from 99 to 104 dpa. TEM observation and micro-hardness measurement were carried out to clarify the irradiation effects on microstructural evolution of 14CrODS ferritic steel at elevated temperature and high dose. Microstructural examination revealed that all of the highly textured- anisotropic grain structures, following heavy irradiation at the temperature above 600$$^{circ}$$C, have not changed. In addition, large regions in all specimens have retained high dislocation density, contained negligible cavitation.

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