Stainless steel (SS) is a well-known material for the internal parts of nuclear power plants. It is known that these alloys exhibit radiation-induced segregation (RIS) at point defect sinks at moderate temperature, while in service. The RIS behavior of SS can be a potential problem by increasing the susceptibility to irradiation-assisted stress corrosion cracking. In this work, the RIS behavior of solute atoms at sinks in SS 316 irradiated with Fe 4+ ions were characterized by atom probe tomography (APT). There were torus-shaped defects along with a depletion of Cr and enrichment of Ni and Si. These clusters are believed to be dislocation loops resulting from irradiation. The segregation of solutes was also observed for various defect shapes. These observations are consistent with other APT results from the literature. The composition of the clusters was analyzed quantitatively almost at the atomic scale. Despite the limitations of the experiments, the APT analysis was well suited for discovering the structure of irradiation defects and performing a quantitative analysis of RIS in irradiated specimens.

Irradiation-induced microstructure in Fe−Cr model alloys, 0.5 MeV-He ion-irradiated at room temperature, was investigated by atom probe tomography (APT). The APT results showed the formation of Cr-atom clustering depending on the ion-penetration depth. Although the Cr-atom clustering was observed in the irradiation damaged zone, this effect was not dominant in the less-damaged zone. In addition, we performed computer simulations using the Metropolis-Monte Carlo (MMC) method for investigating the tendency to form Cr-atom clustering in binary Fe−Cr alloys. The simulation results revealed the formation of Cratom clustering. The degree of Cr-atom clustering for the APT analysis and the MMC simulation was verified by plotting the Cr−Cr radiation distribution function. It was found that the number of Cr atoms, located in the first and second nearest-neighboring sites, increased significantly. Both results support the formation of Cr-clustering, which is believed to be a source of radiation hardening. The application of two techniques, APT and the MMC simulation, provided complementary information on the radiation-induced microstructure.