Computer simulation of the clustering of small vacancies in nickel

Small clusters of vacancies were introduced in a crystal of 4000 atoms at randomly selected positions in Ni. Computer simulations were carried out with the isotropic potential of embedded atom method (EAM) (M.S. Daw and M.I. Baskes, Phys. Rev. B 29 (1984) 6443) at 1200, 1400, 1500, 1600 and 1700K. After MD simulation, the results were output in an interval of 0.2 ps for 40-600 ps to observe the structural relaxation with AVS. In the present work, 40 single vacancies were observed to cluster at 1700K after MD run for 100 ps whereas four single vacancies were not observed for 600 ps. Further MD run is needed for vacancies to agglomerate. Triangular tri-vacancy (3v) also grew to a larger cluster from two tri-vacancies which were initially positioned closer than the other 3v. Four clusters of triangular 15-vacancy were introduced in a crystal. The clusters at first relaxed stacking fault tetrahron (15v-sft). To change the structure of clusters played an important role for the direction of agglomerate. At low temperature agglomeration did not occur during MD calculation.