Ion irradiation has been considered as a surrogate for reactor irradiations and has been widely used due to its versatility including high damage rate and low radioactivity. However, the several orders of magnitude higher damage rate of ion irradiation may result in different microstructures and mechanical responses compared with reactor irradiation. Therefore, it is imperative to systematically investigate the quantitative fidelity of ion beam simulation of the neutron irradiation. Due to the simultaneous production of helium in the reactor, a combined implantation of helium with the heavy ions (Fe) was used in this project (fission reactor-relevant value of ~0.1 appm He/dpa) at a temperature about 60 ℃ higher than the corresponding neutron irradiation. The detailed microstructure characterization will focus on the dislocation loops, cavities, G phases, and element segregation on the grain boundaries which are the important factors on the degradation of the mechanical properties under irradiations. A successful simulation requires high similarities in not only neutron-modified microstructures but also neutron-induced bulk properties with those caused by ion irradiation. However, the accurate investigations on the comparison of mechanical properties between neutron and ion irradiations are rare. Besides, the correlation between microstructures and mechanical properties has not been rigorously evaluated. The correlation will provide a promising way to predict the performance of structural materials based on rapid-turnaround ion irradiations.



We proposed to examine five BOR 60 reactor irradiated samples at temperatures of 376, 459 and 462 ℃, with damage level from 17 to 31 dpa, and five dual-ion irradiated samples of grade 91 and HT-9 ferritic/martensitic steels and Alloy 800H at temperatures of 445, 460 and 520 ℃, with damage level at 16.6 and 72 dpa. TEM characterizations will be used to quantify the size and density of dislocation loops, cavities and G phases. And the quantitative results will be applied to the proper hardening models for comparison with the nanoindentation measured hardness on both neutron and dual-ion irradiated samples. We expect a comparable microstructure and hardness will be achieved from the neutron and dual-ion irradiation with a temperature shift of about 60 ℃ on a same alloy. The experiments are expected to start in June 2022 and to be completed before August 2022.

The research goal of this project is to systematically investigate the microstructure evolution and mechanical properties of neutron and dual-ion irradiated T91, HT9 and 800H alloys at varied temperatures and damage levels to demonstrate the quantitative fidelity of ion beam simulation of the neutron irradiation. The research goal and investigated materials are in line with the DOE’s Office of Nuclear Energy mission, i.e., deployment of advanced nuclear reactors and supporting a diversity of designs that improve resource utilization. Ion beam can significantly reduce the irradiation time compared with neutron irradiation, which will accelerate the research on material degradation under irradiation. 9-12% Cr ferritic-martensitic (F/M) steel (T91, HT9) and austenitic alloy 800H are promising candidates for the structural components in Generation IV fission reactors (such as liquid metal fast reactors and molten salt reactors) due to high temperature performance, good swelling and corrosion resistance. However, the accurate investigations on the comparison of mechanical properties between neutron and ion irradiations are rare. Besides, the correlation between microstructures and mechanical properties has not been rigorously evaluated. By using nanoindentation technique, the mechanical properties of neutron and dual-ion irradiated samples can be obtained easily. TEM characterization will provide a comprehensive understanding of the microstructure evolution and the correlation of microstructures with mechanical properties using proper hardening models. This work will extend our knowledge of the ion beam simulation of neutron irradiation, which will provide a promising and convincible way to accelerate the irradiation study on the structural materials that meet the DOE/NE mission in the advanced reactors.