An ab initio molecular dynamics study: liquid-Al/solid-TiB2 interfacial structure during heterogeneous nucleation

The structural properties of the liquid/solid interface between a TiB2 substrate and Al melts during a nucleation process are investigated using ab initio molecular dynamics simulation at 2 K undercoolings. Different ordered structures are formed on the interfaces with different terminations of TiB2 (0 0 0 1) surface, which determines the nucleant potency of TiB2 particles. It is found that five Al layers stacking like fcc-Al (1 1 1) planes on the Ti-terminated surface naturally extend into the liquid region, which is helpful in effective heterogeneous nucleation. In contrast, the heterogeneous nucleation of α-Al on the B-terminated surface is frustrated by both the AlB2-like structure formed within the first Al layer and the area with sparse Al atoms between the localized Al layer and liquid regions. An evaluation factor based on the Z-directional projection is proposed to quantitatively characterize the in-plane ordering, which could draw a clear boundary between the quasi-solid region and the liquid phase in the liquid/solid interface system.