  Homogeneous nucleation from aluminum (Al) melt was investigated by
million-atom molecular dynamics (MD) simulations utilizing the second nearest
neighbor modified embedded atom method (MEAM) potentials. The natural
spontaneous homogenous nucleation from the Al melt was produced without any
influence of pressure, free surface effects and impurities. Initially
isothermal crystal nucleation from undercooled melt was studied at different
constant temperatures, and later superheated Al melt was quenched with
different cooling rates. The crystal structure of nuclei, critical nucleus
size, critical temperature for homogenous nucleation, induction time, and
nucleation rate were determined. The quenching simulations clearly revealed
three temperature regimes: sub-critical nucleation, super-critical nucleation,
and solid-state grain growth regimes. The main crystalline phase was identified
as face-centered cubic (fcc), but a hexagonal close-packed (hcp) and an
amorphous solid phase were also detected. The hcp phase was created due to the
formation of stacking faults during solidification of Al melt. By slowing down
the cooling rate, the volume fraction of hcp and amorphous phases decreased.
After the box was completely solid, grain growth was simulated and the grain
growth exponent was determined for different annealing temperatures.
