Cooling rate dependence of structural properties of aluminium during rapid solidification

Constant-pressure molecular dynamics simulations and a systematic analysis of the local atomic structures have been performed to study the structural evolution of aluminium on different cooling runs. The regular and defective icosahedral atomic configurations depend strongly on the cooling rate, which is responsible for the cooling rate dependence of the enthalpy. In the simulated amorphous aluminium there exist three kinds of microstructure unit that do not depend on the cooling rate. Two of them are similar to those in the fcc crystal containing interstitialcy and hardly change with decreasing temperature after the glass formation. The third can be considered as crystal germs. Our results also suggest that there exists a critical cooling rate below which the icosahedra form a percolating cluster and the glass exhibits high stability. At a certain quenching rate that is slower than this critical cooling rate, the strength of the icosahedron clusters infinite network may have a saturation value, i.e. a maximum. This may be the origin of the existence of an ideal quenching rate at which the glass exhibits the highest structural stability.