Molecular dynamic simulation of the atomic structure of aluminum solid-liquid interfaces

In this paper, molecular dynamic (MD) simulation was used to investigate the equilibrium atomic arrangement at aluminum solid-liquid (S/L) interfaces with {111}, {110} and {100} orientations. The simulation results reveal that the aluminum S/L interfaces are diffuse for all the orientations, and extend up to 7 atomic layers. Within the diffuse interfaces there exists substantial atomic ordering, which is manifested by atomic layering perpendicular to the interface and in-plane atomic ordering parallel to the interface. Atomic layering can be quantified by the atomic density profile (rho(z)) while the in-plane atomic ordering can be described by the in-plane ordering parameter (S(z)). The detailed MD simulation suggests that atomic layering at the interface always occurs within 7 atomic layers independent of the interface orientation while the in-plane ordering is highly dependent on the interface orientations, with the {111} interface being less diffuse than the {100} and {110} interfaces. This study demonstrates clearly that the physical origin of the diffuse interface is atomic layering and in-plane atomic ordering at the S/L interfaces. It is suggested that the difference in atomic layering and in-plane ordering at the S/L interface with different orientations is responsible for the observed growth anisotropy.