The atomic structure, mechanical and thermodynamic stability of vacancy clusters in Cu were studied by atomistic simulations. The most stable atomic configuration of small vacancy clusters was determined. The mechanical stability of the vacancy clusters was examined by applying uniaxial and volumetric tensile strains to the system. The yield stress and yield strain of the system were significantly reduced compared with the perfect lattice. The dependence of vacancy formation and binding energy as a function of strain was explored and could be understood from the liquid-drop model. It was found that the formation energy of the vacancy clusters decreases monotonically as a function of the uniaxial strain, while the formation energy increases first then decreases under the volumetric tensile strain. The thermodynamic stability of the vacancy clusters was analyzed by calculating the Helmholtz free binding energy and the total probability of dissociation of the vacancy clusters at 300 and 900K under uniaxial and volumetric strains. It was found that although most of the vacancy clusters appear to be thermodynamically stable, some of the intermediate sized clusters have a high probability of dissociation into smaller clusters.

Structure, Mechanical and Thermodynamic Stability of Vacancy Clusters in Cu. Q.Peng, X.Zhang, G.Lu: Modelling and Simulation in Materials Science and Engineering, 2010, 18[5], 055009