Molecular dynamics simulation of the atom cluster evolution in copper melt during solidification process

The structure evolution of atom cluster in copper melt and the microstructure of solidificated copper during the solidification process were investigated by using the molecular dynamics simulation method. It was found that the solidificated structure is composed of crystal phase and amorphous phase when the cooling rate is ranged from 10 ^12.6 to 10 ^14.5 K/s. All the structures of the growing crystal, the critical nuclei and the atom cluster in copper melt are the layer mosaic structure constructed by fcc and hcp structure, which indicates that the layer mosaic structure of copper originates from the nucleation. When the cooling rate is lower than 10 ^13.3 K/s, the atom number of hcp structure in the layer mosaic structure in the amorphous matrix is less than that of fcc structure, but when the cooling rate is higher than 10 ^13.3 K/s, the atom number of fcc structure in the layer mosaic structure is less than that of hcp structure. When the size of the atom cluster with the crystalline structure in copper melt is smaller than the critical size of the homogenous nucleation nuclei, radial distribution function cannot reflect out the feature of crystalline structure though the HA bond-type index have confirmed the presence of a certain number of atom bond of crystalline structure.