Structures and energies of vacancy-Cu clusters in α-Fe

Abstract

We study structures and energies of vacancy-Cu clusters in $\ensuremath{\alpha}$-Fe, which provide fundamental information for understanding the mechanism of neutron-irradiation embrittlement of nuclear reactor pressure vessel materials. Extensive molecular-dynamics (MD) and Monte Carlo computer simulations with the use of the embedded atom method (EAM) potential for the Fe-Cu system are performed to obtain energy-minimum structures of vacancy-Cu clusters of various sizes in a $\ensuremath{\alpha}$-Fe matrix. We find that, in general, a vacancy-Cu cluster consists of a vacancy cluster buried at the center of a Cu shell. The formation energies for the vacancy-Cu clusters are calculated from the MD results, and we develop an equation describing the formation energy as a function of the numbers of vacancies and Cu atoms. We find that the number of Cu atoms on the surface of the vacancy cluster plays an important role in determining the formation energy of the vacancy-Cu clusters. The binding energies of a vacancy and a Cu atom to the vacancy-Cu clusters are also calculated. We find that the interaction between vacancies and Cu atoms enhances the binding of the vacancy-Cu clusters.