Nucleation of copper-vacancy clusters in bcc-Fe: An atomistic study

Copper-rich precipitates are assumed to be the main cause of hardening and embrittlement of Cu-bearing reactor pressure vessel steels since they act as obstacles to dislocation motion within the grains of the polycrystalline bcc-Fe. Multiscale modeling contributes to a better understanding of point-defect-enhanced formation of these clusters during reactor operation. Rate theory is an efficient tool to simulate the cluster evolution on realistic time and length scales. However, many parameters used in rate theory, such as the diffusion coefficients of mobile species and the free binding energies of clusters, are not very well known from experimental investigations. Atomic-level computer simulations can provide these data. In the present work the nucleation free energy is determined for pure copper and pure vacancy clusters as well as for mixed clusters up to a maximum cluster size of 200. The energetics of the coherent CunVm clusters in bcc-Fe is obtained using a combination of on-lattice Monte Carlo simulations and off-lattice molecular dynamics. The most recent Fe-Cu interatomic potential by Pasianot and Malerba [1] is employed in the calculations.
[1] R. C. Pasianot and L. Malerba, J. Nucl. Mater. 360, 118 (2007).