Molecular Dynamics Simulation Of Solidification Behaviors And Structure Of Metals

In this thesis, with the molecular dynamics method and EAM multi-body potential function, the solidification behaviors of silver, copper and nickel under different conditions were simulated and the results were compared with the predicted results according to solid-liquid interfacial energy of metal.By using different EAM multi-body potential functions, the homogenous nucleation undercoolings of Ag, Cu and Ni under different cooling rate were simulated. Moreover, the dependences of homogenous nucleation undercooling on the ratio of sample volume to cooling rate for Ag, Cu and Ni were predicted according to solid-liquid interfacial energy model. The results show that the homogenous nucleation undercooling of metals decreases with increasing ratio of sample volume to cooling rate. The homogenous nucleation undercoolings predicted from the crystal-melt interfacial energy model for silver, copper and nickel agree well with the results simulated by us and the experimental results reported.By means of the radial distribution function curves, the energy curves of the solidification and the final configuration of Ag, Cu and Ni, the critical cooling rates to form ideal metallic glass for silver, copper and nickel were simulated by molecular dynamics method and predicted according to the crystal-melt interfacial energy model. It is found that the solidification structures are composed of crystal phase and amorphous phase when the cooling rate is in the range from 1011.4 to 1014K/s for silver,1011.6 to 1014K/s for copper and 1011.8 to 1014.5K/s for nickel. And the critical cooling rates to form ideal metallic glass for silver, copper and nickel are determined to be 1014,1014 and 1014.5 K/s, respectively. The simulated results of the critical cooling rates to form ideal metallic glass for silver, copper and nickel are almost equal to the predicted results from the crystal-melt interfacial energy model.The structure of atom cluster in copper melt and the evolution during the solidification process were investigated by using the molecular dynamics simulation method. 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 atoms, which indicates that the layer mosaic structure of copper originates from the nucleation, but does not result from the crystal growth process. When the cooling rate is lower than 1013.3K/s, the atom number of HCP structure in the layer mosaic structure in the amorphous matrix is less than that of FCC structure; when the cooling rate is higher than 1013.3K/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.