New insights into radiation damage in additively manufactured alloy 718

Alloy 718 is one of the microstructural complex materials used in nuclear reactors. Additive manufacturing offers new deployment options but introduces unique structural features that complicate radiation damage behaviors, which remains largely unexplored. Here, we investigated the impacts of dislocation cells, cell boundary segregation, and precipitation on radiation damage in seven structural variants of additively manufactured (AM) 718 through thermal separation. Annealing isolated as-built dislocation cells and cell boundary segregation, while thermal aging incorporated γ'/γ″ nanoprecipitates or δ phase. These variants were then subjected to 1 MeV He⁺ ion irradiation at 400, 500, and 600 ℃ to a fluence of 5 × 10¹⁶ ions/cm². Results show that dislocation cells and dislocations in AM variants effectively absorbed interstitial clusters and delayed Frank loop evolution. However, cell boundaries, exhibiting an interstitial bias, accelerated helium swelling. Among the various variables, the matrix Nb and Ti contents have the most significant effect on helium swelling. High Nb and Ti levels enhance defect trapping, which bind vacancies and promote defect recombination, reducing steady-state defect concentrations and delaying defect evolution. In contrast, Nb and Ti depletions, either due to segregation or γ′/γ″ and δ precipitations, accelerate dislocation loop formation and helium swelling, with δ-containing samples exhibiting the most severe effects. The as-built 718 alloy exhibited lower loop formation incubation dose and increased swelling compared to recrystallized counterpart. Thermal-aged variants with γ'/γ″ and δ precipitates promoted loop evolution and swelling compared to non-aged variants. Therefore, AM 718 is recommended to be homogenized or recrystallized for solution-annealed variant and avoid δ precipitation for precipitation-hardened variant. This is an initial study using thermal separation to clarify the individual impacts of dislocation cells, segregation and precipitations on the radiation effects in AM 718, providing guidelines for its nuclear applications.