A Molecular Dynamics Simulation Study On The Solidification Process Of Liquid Metal Nickel

The rapid solidification processes of transitional metals have been considered to be a hot and difficult point for computer simulation study due to the complexity of their outer electrons. At present, various kinds of potential have been adopted in simulations, of which only the EAM potential has been widely applied, so the original program used before now, adapting energy independent non-local model pseudo-potential, has been modified to meet the need of EAM potential. Owing to the EAM potential parameters, in general, obtained by directly fitting to the physical properties of solid metals, for obtaining more accurate results in the simulation of solidification processes, it is necessary to reflect the differences between the structures of liquid and solid metals in the potential and make a suitable modification to the concrete form of potential. A lot of experiments have demonstrated that during solidification processes the cooling rate has an important effect on the transition speed and the final results of microstructures, however, their microscopic mechanisms have not deeply investigated up to now. Based on this thought, the main works in this paper are completed as follows:(1) By improving the original program used before now and using the modified EAM potential to describe the inter-atomic interaction in the system of liquid transitional metal, the rapid solidification processes of liquid transitional metal Ni have been simulated. And comparing these results with those obtained by using Quantum Sutton-Chen potential, it is found that the modified EAM potential can more accurately describe the inter-atomic interaction in the system.(2) Performing the simulation study of liquid metal Ni system, the emphasis is to consider the effects of cooling rate on the transition speed of microstructures and the structures formed in the end. It is found that the cooling rate plays a critical role in the formation of solidifying microstructures. When the cooling rates are in the range from 1.0×10¹⁶ K . s^-1 to 4.0× 10¹³ K. s^-1 , the structures in the system have not obvious change and the amorphous structures formed for all the cooling rates; while when the cooling rates are in the narrow range of 4.0×10¹³ K.s^-1 to 3.5×10¹³ K.s^-1, the essential transitions of structures are happened from amorphous to partial crystal structures, in which the fcc and hep structures are the main parts and co-exist in the system; and as the cooling rates in the range from 3.5×10¹³ K.s^-1 to 1.0×10¹² K.s^-1 , the structure transitions suddenly happened from the fcc and hep structures as the main part and co-existed in the system to the crystal structures in which only the fcc structures...