First-principles calculations on Al/AlB2 interfaces

The AlB₂ (1 1 1) surfaces and Al (1 1 1)/AlB₂ (0 0 0 1) interface were studied by first-principles calculations to clarify the heterogeneous nucleation potential of α-Al grains on AlB₂ particles in purity aluminium and hypoeutectic Al-Si alloys. It is demonstrated that the AlB₂ (0 0 0 1) surface models with more than nine atomic layers exhibit bulk-like interior, wherein the interlayer relaxations localized within the top three layers are well converged. The outmost layer of AlB₂ free surface having a preference of metal atom termination is evidenced by surface energy calculations. With Al atoms continuing the natural stacking sequence of bulk AlB₂, Al-Al metallic bonds are formed across interface during the combination of Al atoms with Al-terminated AlB₂ surface. The calculated interfacial energy of the Al/AlB₂ interface is much larger than that between the α-Al and aluminium melts, elucidating the poor nucleation potency of α-Al grains on AlB₂ particles from thermodynamic considerations.