Size and Temperature Dependence of the Point Defect Binding Free Energy to Defect Clusters in bcc Fe

Size and temperature dependence of the point defect binding free energy has numerically evaluated for self-interstitial atom (SIA) clusters and vacancy clusters in bcc Fe by using continuum models based on thermo-dynamics and linear elasticity. The estimated binding free energy of SIAs to SIA-clusters is much higher than that of vacancies to vacancy clusters, indicating that SIA-clusters are more thermally stable than vacancy clusters. For relatively small clusters, the estimated binding free energy at 0 K is comparably consistent with atomistic cal-culation data; and then, the SIA binding free energy at 850 K is averagely about 35% lower than that at 0 K, while the vacancy binding free energy is about 6% lower; which may remarkably affect the formation kinetics of those defect clusters under irradiation. These kinds of information will be one of the basic parameters for a theoretical model of the microstructural evolution of Fe-based materials in the nuclear fusion DEMO environment. (C) 2022 The Japan Society of Plasma Science and Nuclear Fusion Research