Improvement of Radiation Resistance of Alumina Scales Formed on FeCrAl ODS Alloys by Microstructure Control

Research Project

Project/Area Number	23K13684
Research Category	Grant-in-Aid for Early-Career Scientists
Allocation Type	Multi-year Fund
Review Section	Basic Section 31010:Nuclear engineering-related
Research Institution	Tohoku University
Principal Investigator	余浩東北大学, 金属材料研究所, 助教 (10825871)
Project Period (FY)	2023-04-01 – 2025-03-31
Project Status	Granted (Fiscal Year 2023)
Budget Amount *help	¥4,030,000 (Direct Cost: ¥3,100,000、Indirect Cost: ¥930,000) Fiscal Year 2024: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000) Fiscal Year 2023: ¥2,470,000 (Direct Cost: ¥1,900,000、Indirect Cost: ¥570,000)
Keywords	FeCrAl ODS / alumina / irradiation / microstructure control / Radiation Resistance / Alumina Scale
Outline of Research at the Start	Alumina-forming FeCrAl oxide dispersion strengthened (ODS) alloys are considered as the enhanced accident tolerant fuel cladding for light water reactors. Stable alumina scale with high radiation resistance are necessary. The proposal aims to improve the radiation resistance of the alumina scale.
Outline of Annual Research Achievements	Alumina-forming FeCrAl ferritic oxide dispersion strengthened (ODS) alloys are claimed as one of the preferable materials for next generation nuclear systems. This proposal aims to improve the radiation resistance of alumina scales formed on FeCrAl ODS alloys through microstructure control. The first year of research explored the effects of pre-oxidation temperatures and excessive oxygen (Ex. O) content on the microstructure and mechanical properties of the alumina scales formed on the FeCrAl ODS alloys. The alumina scales formed at different pre-oxidation temperatures and Ex.O contents were characterized by scanning electron microscope (SEM), electron probe micro-analyzer (EPMA) and transmission electron microscope (TEM). Nanoindentation and ultra-small double-notched shear (DNS) compression method were performed to measure the stress-strain behavior and adhesion strength of the formed alumina scales.
Current Status of Research Progress	Current Status of Research Progress 2: Research has progressed on the whole more than it was originally planned. Reason The first year was conducted according to the initial experimental plan for alloy fabrication and pre-oxidation for alumina formation. FeCrAl ODS alloys with nominal compositions of Fe-15Cr-7Al-0.4Zr-0.5Y2O3-(0.21, 0.28) Ex. O (wt%) were fabricated using mechanical alloys (MA). Pre-oxidation was performed from 900 oC to 1100 oC under air condition. Alumina scales formed on FeCrAl ODS alloys were characterized by X-ray diffraction (XRD), SEM and EPMA. The dispersion of Y-Zr oxide particles inside the formed alumina at various pre-oxidation temperatures was investigated by scanning transmission electron microscopy (STEM) imagings and X-ray energy dispersive spectroscopy (EDS) elemental maps. DNS compression tests were performed on the interface of alumina and FeCrAl ODS alloys formed at various temperatures, and this method was demonstrated to be capable of quantitatively assessing the adhesion strength of alumina scales.
Strategy for Future Research Activity	In the following year, it will focus on the effect of irradiation on alumina scales formed at different pre-oxidation temperatures. The pre-oxidized samples will be irradiated by using simulation ion irradiation technique in CYRIC, Tohoku University. After the irradiation-processing, TEM observation is performed to investigate the microstructural evolution of alumina scales and the Y-Zr oxide particles. In order to assess the adhesion strength of the alumina scales before and after irradiation, the DNS compression test will be performed at the interfaces between the alumina and the FeCrAl ODS alloy located in the irradiated and unirradiated areas, respectively.