The Study On The Solidfication Process Of Metal Micro-nucleation Based On Molecular Dynamics

The research of micronucleation is alway the focus of attention in the process of metal solidfication.In order to reveal the behavior of interaction between atoms,this article uses the scanning microscope and electron microscope to observe and to analyze the microstructure of Al alloy of different components in nucleation area of equilibrium freezing;we use Material studio software to simulate the behavior of interaction between atoms for nucleation area.In this paper,we use the stability of the structure of atomic clusters to reflect the process of atomic nucleation.The binding energy value of the lattice structure of different atomic clusters is used as a criterion about the stability of the lattice structure.The nucleation zone mentioned in this article is the area of equilibrium freezing,the lattice structure is the calculation model established by the Material studio software.Based on the theoretical model of MAEAM modified multibody potential,this article simulates the behavior of interaction between atoms in the process of equilibrium freezing,the nucleation mechanism of atomic stacking growth were studied from the atomic scale,to find out the relationship between the microstructure of nucleation area of equilibrium freezing and macroscopical products so as to make analysis for the process of crystallization nucleation.The following conclusions based on experiental investigation and simulation analysis show that:the key factors of the stability of atomic clusters in the nucleation zone are the lattice structure of atoms clusters、the numbers of atomic nucleation、electronic structure of atoms and the lattice energy state.In the process of equilibrium freezing,the numbers of atomic nucleation have an threshold,the lattice have the best stability in the threshold,whatever lower or higher than this value,the lattice structure stability will decline.According to the numerical simulation,when the numbers of atomic nucleation are 14,the average of atomic energy minimum is-55.11ev.According to the high resolution TEM images,it is consistent that the 2.67?spacing value of lattice is compared with reference of2.86?after Al crystallization nucleation.The electronic structure around metal atoms determines the numbers of electronic and the degree of electronic overlap.The more electrons and the higher the degree of electronic overlap,the lattice structure is the more stable.By analyzing TEM images of Al and Al alloy,it has been found that the atoms in nucleation area are arranged in general rules and tidy and not obvious dislocation.The crystal growth direction of Al₂Cu metal compounds is（001）surface in nucleation area.The crystal growth direction ofɑ-Al is（111）surface in nucleation area.In addition,we also calculate the series of Al-Cu alloy with different contents of Cu atoms and Al-12.6%Si alloy.Conclusion show that:（1）its products is gradually transiting from single-phase substitutional solidsolution to metal compounds with the increase of the content of Cu atoms;（2）when the Al-2%Cu and Al-12.6%Si alloy form single-phase substitutional solid solution,the binding energy value is-330.79ev and-78.22ev,when Al-33.2%Cu mainly form intermetallic compounds Al₂Cu,its binding energy values is360.38ev.