Atomistic modeling and molecular dynamic simulation of binary metallic glasses

Bulk metallic glasses (BMGs) have great potentials because of their unique outstanding mechanical and physical properties. However, the fundamental principles guiding the discovery of new BMGs have not been systematically developed. In this work, the glass forming ability (GFA) of binary metallic systems has been investigated by using molecular dynamic simulations. A series of interatomic potentials representing different atomic size ratios and chemical bonding of the constituent atoms were constructed to demonstrate the effects of the size ratio, concentration of the minority atoms and compositional short range order (CSRO) on the GFA. The phase diagrams of glass transition were built to represent the glass formation in the quenching process. We found that when the atomic size ratio should be limited in a range to form a binary metallic glasses. The addition of the solute atoms always improves the GFA of the modeling system. The size ratio factor, defined as the product of the size mismatch and the minimum concentration of the solute atoms, has been used to quantitatively describe the GFA. CSRO, introduced by applying the repulsive potential between small sized atoms, improves glass formability, and makes small atoms have slower dynamics and lower diffusivity than large atoms.; Al-Ni binary system was studied with Finnis-Sinclair potential to describe atomic interactions. We investigated the transitions of Al₈₀Ni₂₀ systems at two cooling rates, and found that there exist octahedral local clusters in the amorphous AlNi alloys. The strong Al-Ni interaction and weak Ni-Ni interaction leads to preferred Al atoms neighborhood for Ni atoms. This type of the chemical bonding is similar to the CSRO introduced in the modeling system. The studies of the relaxation time reveal that the small sized Ni atoms actually have slower dynamics than Al atoms. It is in agreement with that of the modeling system and suggests that the size mismatch and CSRO play key roles in determining the GFA of BMG materials.