The study of ion irradiation damage in Low-Cr FeCrAl oxide dispersion strengthened ferritic steels

  • Hoang Le

Student thesis: Doctoral Thesis


FeCrAl Oxide Dispersion Strengthened (FeCrAl-ODS) alloys has a body-centered cubic structure (BCC) and has high oxidation and corrosion resistance, high melting point, good radiation tolerance and swelling resistance. FeCrAl-ODS alloys is an excellent candidate for fuel cladding material for fission reactors and first wall structure material for fusion reactors, however, one of the main problems is the formation of the Cr-rich alpha prime precipitates either from thermal aging above 748K or by radiation-induced precipitation at lower temperature. The Cr-rich alpha prime precipitates are usually observed in thermally aged and irradiated high Cr ferritic alloys and steels. It has a BCC structure similarly to the matrix with only a slightly higher lattice parameter (2.88Å vs. 2.87Å). Cr-rich alpha prime precipitates are mostly reported in neutron irradiation studies of FeCrAl alloy and have hardly been found in ion irradiation studies until recently. This is assumed to be correlated to the differences in dose rate, cascade size, injected interstitial, and the Cr concentration. It is suggested that the formation of the precipitate by ion irradiation is affected by the irradiation-enhanced diffusion that promotes Cr clustering and the ballistic dissolution process where the precipitates get bombarded with the energetic displacement cascade and diffuse the Cr back to the Fe matrix.

In this work, a series of ion irradiation studies have been conducted on a commercial FeCrAlODS alloy – PM2000 and the newly developed low-Cr FeCrAl-ODS alloys from Nippon Nuclear Fuel Development (NFD) and Oak Ridge National Laboratory (ORNL) to study the radiation damage resistance of each material. The series of self-ion study have found that the ORNL-ODS and NFD-ODS are less susceptible to the formation of Cr-rich α’ precipitates under the effect of ion irradiation at a variety of conditions than the high-Cr PM2000. The microstructure evolution at each irradiation damage dose was observed by BFTEM, and postirradiation examination (PIE) was conducted with STEM-HAADF, EDS and EELS. The
formation of irradiation-induced Cr-rich α’ precipitates occurred at lower temperature and higher dose damage rate than previously reported in literature, with more precipitation found at room temperature. The He implantation study shows that the He bubble formation in NFDODS alloy was suppressed the most due to the higher number of nano-oxide particles. Heterogeneous bubble formation was observed with larger He bubbles found in the Y-Al-O oxide cluster region, which could be due to the lower surface energy of the oxide. The initial results of the dual beam experiment consist of Fe and He ion irradiation on PM2000 shows a slight decrease in bubble sizes at the same He implanted concentration and no phase transformation. The final set of Xe ion irradiation is to test the integrity of the alloy and the oxide particles at very high radiation damage. It is observed that the oxide particles are stable at a maximum of 53 DPA and show no sign of oxide dissolution.
Date of Award11 Jan 2024
Original languageEnglish
SupervisorJonathan Hinks (Main Supervisor), Steve Donnelly (Co-Supervisor), Anamul Haq Mir (Co-Supervisor) & Konstantina Lambrinou (Co-Supervisor)

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