Fast neutron irradiation-induced hardening in Inconel 625 and Inconel 718 fabricated via laser powder bed fusion

Inconel 625 (IN625) and Inconel 718 (IN718) samples were fabricated using laser powder bed fusion (L-PBF) and the effects of neutron irradiation on their microhardness were investigated. Samples were either left in their as-printed condition or heat treated at 700 °C, 900 °C, or 1050 °C for 1 h to understand the influence of microstructure size and phase on radiation resistance. Heat treated wrought IN625 and IN718 samples were also inspected for experimental control. Samples were irradiated for either 7, 12, 17, or 22 weeks to show the effects of cumulative radiation. Employed fast neutrons were a by-product from a positron emission tomography (PET) cyclotron, used to create radioisotopes for medical purposes, located within the University of Missouri Research Reactor (MURR). Vickers microhardness was measured on inspected samples before and after fast neutron irradiation to quantify radiation hardening and softening effects. Results show that IN625, particularly when heat treated, experienced initial hardening followed by softening with increasing neutron fluence. IN718, on the other hand, exhibited higher resistance to radiation-induced hardening and softening. The 700 °C heat-treated L-PBF samples of both alloys demonstrated the least softening, suggesting superior radiation resistance due to PBF-induced micro-segregation and post-PBF stress relief. The findings highlight the complex interplay between microstructure, precipitate evolution, and radiation damage in determining the mechanical response of nickel-based superalloys to neutron irradiation, which is crucial for the development of radiation-resistant materials for nuclear applications.