Vibrational Effects on Thermodynamics of Copper-Vacancy Clusters in bcc-Fe

The irradiation-enhanced formation and evolution of Cu-rich precipitates in reactor pressure vessel steels are multiscale phenomena. These processes can be effectively investigated by rate theory using thermodynamic parameters which must be obtained from atomistic simulations. The present work reports on the vibrational effects on the thermodynamics of nanoclusters consisting of vacancies and/or Cu. The most recent Fe-Cu interatomic potential by Pasianot and Malerba is used. The vibrational density of states obtained from dynamical matrix method is used to evaluate the phonon contributions to the free energy of formation and free binding energy of defect clusters. Pure bcc-Fe and pure fcc-Cu are used as references. The vibrational effects on total free energy of pure bcc-Fe and pure fcc-Cu are compared with available CALPHAD data and literature data obtained by first-principle calculations or other interatomic potentials. The absolute value of the total free binding energy decreases for pure vacancy clusters with increasing temperature, while the increase is observed for pure Cu clusters. Mixed vacancy-Cu defect clusters show the non-uniform behaviour in the absolute value of the total free binding energy .