Defect microstructure and hardening in uniformly damaged long-range-ordered (Fe, Ni)₃V alloy under 528 MeV Xe ion irradiation

L1₂-type (Fe, Ni)₃V alloy is a promising candidate for high-temperature structural components. In this study, we investigated its defect microstructures and hardening response after creating a uniform 8 μm damage layer with 528 MeV Xe ions (350 °C/3 dpa). The alloy exhibited good phase stability in the ion-irradiation damaged layer. Microstructural analysis revealed production of irradiation-induced dislocation structures (both loops and lines) with a uniform density of 3.3 × 10¹⁴ m/m³. No void swelling was observed. Dislocation loops dominated the total dislocation density, exhibiting a mild increase in mean size with depth (from 9.0 nm to 12.3 nm), driven by an enhanced tendency for one-dimensional (1D) ordering at greater depths. This reflects the migration and elastic interaction of ½<110> loops, which account for 83.1 % of the loop population and suggested to be mostly of interstitial nature by a high-voltage electron microscopy (HVEM) based approach. A minor fraction (∼16.9 %) of ⅓<111> Frank loops was also confirmed, the presence of which might stem from the breakdown of a small number of pre-existing ordered domains. The irradiation-induced hardening was measured at 0.55 GPa (∼11.8 %), a consequence of the pinning effect of the ½<110> loops impeding slip activation. These findings demonstrate the attractive potential of L1₂-type (Fe, Ni)₃V alloy for withstanding the lower end of operational temperatures and a benchmark damage dose anticipated in multiple nuclear reactor applications.