Nucleation has a dominant effect on the microstructure and mechanical properties of alloys. But it is difficult to investigate the kinetic details of the nucleation experimentally. In order to get more information in the initial stage of the nucleation, computer simulation is widely used for the study of the nucleation process. This paper simulates the solidification process of a real alloy system Ni3Al under different conditions using Molecular Dynamic simulation method. The energy, clusters and microstructures in the initial stage of nucleation are presented. The main contents and results are as follows:
1. The solidification of Ni3Al alloy at 780K is simulated using Molecular Dynamic simulation method based on Baskes’s embedded atomic potential. The kinetic details of the nucleation are investigated. It is indicated that there are a large number of crystal embryos in the supercooled liquid at the early stage of the nucleation. The crystal nucleus forms through structure fluctuation and composition selection. Although the glass clusters dominate in the supercooled liquid system, they are not stable and kinetically do not participate in the formation of crystal nucleus. The nucleus is a random mixture of a large number of FCC structure and a small number of distributed HCP structure. The critical nucleus is not a complete sphere but shows an irregular shape.
2. The solidification of Ni3Al alloy cooled at the rate of 1011K/s from 2000K to 300K is simulated. It is demonstrated that the system energy changes rapidly and the radial distribution function transforms from the supercooled liquid structure to crystal structure during the cooling period from 900K to 800K. The numerical results show that the number of glass clusters increases with the decrease of the temperature before the transformation. When the crystal clusters appear in the system, the number of glass clusters decreases quickly and disappears before the beginning of nucleation. The stable FCC structure exists since the appearance of the crystal embryos. The eventual crystal nucleus is a random mixture of FCC structures and HCP structures.
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