| dc.description.abstract | The purpose of this study is to evaluate oxide dispersoid stability in oxidedispersoid-strengthened (ODS) alloys under different ion irradiation conditions. ODS alloys are considered as future generation IV reactor cladding and in-core structure materials due to their good swelling resistance and high temperature strength. The ferriticmartensitic (FM) 12Cr ODS alloy which has uniform distribution of oxide dispersoids in both phases was selected for this study. Previous studies on this alloy have shown good void swelling resistance after 800 peak dpa Fe ion irradiation at high temperature and have revealed equilibrium oxide dispersoid size dependency of irradiation temperature. It is also found that equilibrium size is closely related to a coherency with matrix. In this study, oxide dispersoid size and density of coherent and incoherent dispersoids were further studied and analyzed as a function of depth for both phases after ion irradiation. Furthermore, He preimplantation study was conducted to see how pre-implanted He bubbles affect coherent dispersoid size and density under irradiation in TM phase, since He is generated by (n,α) transmutation in real reactor which causes He embrittlement. The study revealed that He implantation itself does not affect dispersoid size or density, but subsequent ion irradiation after 1x10^15 ions/cm2 leads to oxide dispersoid density increase, while 1x10^16 ions/cm^2 does not, suggesting that small bubbles promote nucleation of coherent oxide dispersoid. Other factors that affect equilibrium dispersoid size are dpa rate and damage cascade factor. The effect of dpa rate on dispersoid size and density was studied on Hf iii doped ODS alloy, and coherent and incoherent particle size and density were studied as a function of local dpa rate (depth). The result showed no noticeable difference on dpa rate, and in order to explain the experimental observations, defect-assisted-diffusion mechanisms were taken into consideration. A high dpa rate results in enhanced dispersoid dissolution, while dispersoid recovery is increased due to defect-assisted diffusion. Therefore, the two effects are balanced, leading to a relative insensitivity of dispersoid size to dpa rate. The result showed the possibility of utilizing ion accelerator on studying ODS alloys to predict their behavior in real reactor environment. | en |
