Helium ion irradiation resistance of N-doped FeCrAl coatings with nitrogen-induced nanocrystalline/amorphous structures

FeCrAl-based coatings are promising protective candidates for accident-tolerant fuel cladding applications because of their excellent high-temperature oxidation resistance and favorable thermal properties. However, their irradiation tolerance remains a critical concern, particularly because helium accumulation can induce bubble formation, swelling, and mechanical degradation. In this study, nitrogen was introduced into magnetron-sputtered FeCrAl coatings to construct nanocrystalline/amorphous composite structures for enhanced helium ion irradiation resistance. The effects of N 2 flow rate (0–12 sccm) on the microstructure, irradiation damage behavior, and mechanical properties of the coatings were systematically investigated under 60 keV He + irradiation. The results show that nitrogen incorporation promotes nitride formation and structural disordering, leading to the formation of a nanocrystalline/amorphous composite structure. The coating deposited at 6 sccm exhibits an interface-rich nanocrystalline/amorphous architecture and shows substantially reduced irradiation-induced swelling, surface openings, and large cavity formation compared with the undoped coating. This improved irradiation tolerance is closely correlated with the N-induced heterogeneous microstructure, which may facilitate the accommodation and redistribution of irradiation-induced defects and implanted He. Meanwhile, nitride nanocrystals contribute to the retention of relatively high hardness after irradiation. However, excessive nitrogen incorporation leads to predominant amorphization, reducing the density of effective nanocrystalline/amorphous interfaces and weakening the ability of the coating to suppress helium-related damage. These findings clarify the relationship between nitrogen-induced nanocomposite structures and helium irradiation tolerance, providing a useful strategy for designing radiation-resistant FeCrAl-based protective coatings.