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.