Molecular dynamics study on interfaces generated between atomic clusters

The atomic structure of grain boundaries generated in the process of coalescence between copper atom clusters is investigated using the molecular dynamics method. The effective medium theory is adopted as interatomic interaction for precise estimation of surface and defect energies. The effects of cluster size, velocity and crystalline orientation on the atomic behaviour are studied. When cluster size is relatively small, dislocations (detected as stacking faults) generated in the contact region develop throughout the cluster body. On the other hand, in larger-size clusters, stacking faults are multiple and they interact with each other inside clusters. The local atomic structure is effectively assessed by a topological method, by which atoms are recognized as a face-centred cubic (fee) structure or a hexagonal close-packed (hcp) structure. Large approaching velocity results in a flattened shape of clusters and induces complicated propagation of stacking faults, where the critical speed for this transition is estimated at 600-700 m/s approximately. When a slight orientation angle is applied to clusters, the difference in angle is cancelled by the spontaneous spin of clusters. However, when a large orientation mismatch is given to clusters, nucleation and growth of stacking faults are obstructed according to the Schmid factor of slip.