Radiation-enhanced diffusion of copper in iron studied by three-dimensional atom probe

Radiation-enhanced diffusion (RED) of copper (Cu) in iron (Fe) is essential for understanding solute/impurity diffusion in nuclear materials, especially reactor pressure vessel steel, but has been rarely reported experimentally. In this study, we performed a high-precision investigation of RED using well-controlled electron irradiation and three-dimensional atom probe (3D-AP). Cu-Fe diffusion pairs were created using high-purity Fe and Cu as base materials, and irradiated by 2 MeV electron at a temperature of 773 – 893 K controlled to within ±3 K. Cu diffusion into the Fe matrix was observed at the atomic level using 3D-AP, and the diffusion coefficient was obtained directly using Fick's law. RED was clearly observed, and the ratio of diffusion under irradiation to thermal diffusion was increased as the irradiation temperature decreased. RED was quantitatively evaluated using the reaction kinetics model, and the model which consider only vacancies gave a good agreement. This gave experimental clarification that RED was dominated by irradiation-induced vacancies. In addition, the direct experimental results on the effect of irradiation on the solubility limits of Cu in Fe was obtained; solubility limits under irradiation were found to be lower than those under thermal aging.