Enhanced helium ion irradiation tolerance in a Fe-Co-Ni-Cr-Al-Ti high-entropy alloy with L12 nanoparticles

•Helium bubbles and large stacking faulted loops are observed as the dominant structural damage in the He ion irradiated HEA reinforced by L12 nanoparticles.•The L12 nanoparticles provide numerous interfaces for He entrapment and damage elimination, which suppresses He bubble growth.•A correlative TEM/APT characterization reveals that the RIS around He bubbles is dominated by the inverse Kirkendall mechanism.•Irradiation-induced dissolution and re-precipitation of the L12 nanoparticles can retain the main microstructure of the L12-strengthened HEA and provide a sustainable irradiation resistance.