Effects of Helium Implantation on the Deuterium Permeation Behavior in Oxidized Fe-Cr-Al Ferritic Steel

The stability of microstructure and functions under irradiation is a critical issue for tritium permeation barriers (TPBs). High-energy ion irradiation has been an ideal tool for studying the effects of irradiation on the hydrogen isotope permeation behavior of TPBs. However, most studies have concentrated on the effects of displacement damage, with limited research exploring the impact of helium. In this work, we utilized oxidized Fe-Cr-Al ferritic steel (OFFS) with a 100 nm thick Al2O3 layer as the sample. A single-beam helium ion implantation experiment was conducted on OFFS at 400 ℃. Then, deuterium gas-driven permeation (GDP) experiments were conducted. The deuterium permeabilities of irradiated samples were obtained and compared with those of the original samples. Vacancy-type defects in the oxide layer of the samples, both pre- and post-irradiation, were characterized through positron annihilation Doppler broadening spectroscopy (DBS-PA) experiments. The results indicated that the increase in deuterium permeability in OFFS did not exceed one order of magnitude across various irradiation doses. The permeability initially increased at a 24 ppm dose but decreased at a 240 ppm dose. This variation may be attributed to helium occupying a limited number of vacancies at a 24 ppm dose, whereas at a 240 ppm dose, helium forms clusters that inhibit deuterium permeation. For the samples implanted with helium and pre-irradiated with gold ions (sequential gold-helium single-beam irradiation), distinct variations in permeability across various irradiation doses were observed. These variations can be attributed to the competition between vacancy-type defects and helium clusters.