| Abstract Scope |
Structural changes during crystallization and vitrification in dilute face-centered-cubic (FCC) alloys was investigated using model Al-Sm alloys. Molecular dynamics simulations were performed to study the solidification behavior of Al-1at.%Sm and Al-5at.%Sm at 10^10, 10^11 and 10^12 K/s cooling rates. Two structural features were identified from these simulations. In case of Al-1at.%Sm, we learn that, near the melting point, liquid phase manifested pockets of unique transitional structures comprising triangular arrangements in near-parallel layers that encapsulated a FCC-HCP coordinated core. We defined such a structure as the pre-critical nucleus, which is contained within an otherwise predominantly uncoordinated amorphous liquid phase. However, within the range of cooling rates employed, Al-5at.%Sm manifested only amorphous structure after solidification. The liquid structure in the transitional state contained temperature dependent icosahedron clusters that manifested as double-peak in the radial distribution function. Near the Tg Al-5at.%Sm achieves additional local ordering via the formation of inter-penetrating icosahedral frameworks. |