Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Reactor pressure vessel (RPV) steels consist of polycrystalline bcc-Fe with different alloying elements, e.g. Ni, and different impurities, e.g. Cu. The continuous irradiation by fast neutrons leads to a supersaturation of vacancies and self-interstitials which enhances the diffusion of the foreign atoms and causes the formation of nanosized clusters. The interaction of dislocations with these precipitates is considered to be the main cause of hardening and embrittlement of RPV steels. In order to model the evolution of the nanoclusters under irradiation at typical temperatures by rate theory the dependence of their nucleation free energy on cluster size and composition must be known. In the present work atomic-level computer simulations are employed to determine these data since they are hardly obtainable by experimental investigations. The ternary Fe-Cu-Ni interatomic potential by Bonny et al. [1] is used in order to consider the thermodynamics of nanoclusters which may consist of the two foreign species and vacancies. In particular the influence of Ni on the formation of clusters containing Cu and vacancies is investigated since previous theoretical [1] and experimental [2,3] studies indicated synergistic effects. The nucleation free energy of the clusters is determined by the energy and the entropy change due to precipitation using isolated (diluted) Cu and Ni atoms as well as vacancies as the reference. In agreement with experimental observations the nanoclusters are assumed to have the bcc structure of the iron matrix. The energy and entropy contributions are calculated using combinations of on-lattice Monte Carlo simulations and off-lattice molecular dynamics calculations.
[1] G. Bonny et al., Phil. Mag. 89 (2009) 3531.
[2] J. T. Buswell et al., Effects of Radiation on Materials: 14th Int. Symp. (Vol. II), ASTM STP 1046, Philadelphia, 1990, p.127.
[3] F. Bergner et al., J. Nucl. Mater. (2009) in press