2023 Fiscal Year Research-status Report
Stability of nanoscale particles in Oxide-Dispersion-Strengthened (ODS) steels under extremely large and multi-directional deformation conditions
| Project/Area Number |
23K13087
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| Research Institution | National Institute for Fusion Science |
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Principal Investigator |
申 晶潔 核融合科学研究所, 研究部, 助教 (80824747)
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| Project Period (FY) |
2023-04-01 – 2026-03-31
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| Keywords | ODS steel / Microstructure / Ion irradiation / Irradiation effects |
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| Outline of Annual Research Achievements |
The as-fabricated oxide dispersion strengthened (ODS) ferritic steel was recrystallized after large plastic deformation and subsequent heat treatment. The microstructural evolution and hardness changes under single-beam (Fe ions) and dual-beam (Fe and He ions) irradiation up to a peak damage dose of 10.5 displacements per atom (dpa) at elevated temperatures were investigated to clarify the irradiation resistance. Results showed that size and number density of the oxide particles were slightly decreased after ion irradiation. Compared with single-beam irradiation, high density of helium bubbles was observed after dual-beam irradiation. Larger helium bubbles are trapped at the grain boundaries in the as-fabricated specimen, and the size of helium bubbles in the grains is almost the same for both as-fabricated and recrystallized specimens. Nanoindentation hardness was evidently not changed after both single-beam and dual-beam irradiation at 973 K, suggesting that helium bubbles did not significantly induce hardening at this condition.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
In order to make the laboratory-scale ODS steel with a designed chemical composition, adjustment of machine time, such as large glove boxes, hot isostatic pressing etc., is necessary. Also, to control the concentration of the impurities in the fabrication process, specialized parts, high-purity raw materials and atmosphere control should be considered.
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| Strategy for Future Research Activity |
The designed ODS steels are to be made with high-purity raw materials. The coarse Ti-enriched particles are expected to be reduced or controlled by changing the Ti concentration and impurities. Moreover, the behaviors of the oxide particles and Ti-enriched particles during fabrication process will be investigated, and the formation mechanisms and thermal stability after plastic deformation will be elucidated.
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| Causes of Carryover |
The amount of the budget was planned to be used for the maintenance of tensile machines. However, the maintenance was not able to be completed for some reasons from the company. It will be used for the punching dies of discs and tensile specimens, specialized containers and high-purity raw materials for mechanical alloying.
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