Diffusivity of nickel in Fe under 2.8 MeV Fe2+ irradiation at 400 ℃ studied by atom probe tomography

• A new high-precision but relatively simple measurement method for short range ion-irradiation enhanced diffusion. • Diffusion coefficient of Ni into Fe at 400 ℃ under ion-irradiation. • A discussion about oxides on the APT specimen surface caused by high laser energy. The diffusivity of nickel (Ni) in iron (Fe) under irradiation at lower temperatures is of great importance in understanding the formation dynamics of Mn-Ni-Si clusters/precipitates in the reactor pressure vessel (RPV) steels, particularly at the operating temperature of light water nuclear power plants (NPPs). However, the diffusion distance of nickel at a low temperature close to the operating condition of a NPP is extremely shorter than the resolution limit of the common measurement techniques. Therefore, even after long period of thermal ageing and irradiation, the experimental study about the diffusivity of Ni in Fe at these temperatures has been rarely reported. In this study, we attempted to develop a high-precision measurement method to measure the diffusivity of Ni in Fe on Ni-Fe pairs under irradiation at lower temperatures, using a thickness-controlled electroplating technique, well-controlled Fe 2+ irradiation, and atom probe tomography (APT). To demonstrate the viability of this approach, approximately 0.5 µm Ni films were electroplated on high-purity Fe substrates, which were subsequently irradiated with 2.8 MeV Fe 2+ irradiation at a flux of 9.4 × 10 14 ion m −2 s −1 (the estimated damage rate of approximately 7.1 × 10 −5 dpa∙s −1 near the Ni-Fe interface) at temperatures of 400 ± 2 ℃. The diffusion of Ni into the Fe matrix at 400 ± 2 ℃ was successfully observed at the atomic level using APT, and the diffusion coefficient of 7.8 ± (2.4) × 10 −15 cm 2 s −1 was directly estimated using Fick’s second law. The irradiation enhancement factor of approximately 6.4 × 10 4 was also estimated, demonstrating the significant irradiation-enhanced diffusion.