Influence of Ag substitution on the local structure and glass-forming ability of Al86Ni(8-x)Y6Agx (X = 0,1,2) liquids

The local structure of Al₈₆Ni_(8-x)Y₆Ag_x (X = 0,1,2) molten and glassy alloy was investigated by ab initio molecular dynamics simulation. It transpired that the Al₈₆Ni_(8-x)Y₆Ag_x alloy can be considered as a combination of Ni- and Y-centred Al clusters with Ag as ‘glue atoms’. First and second Ag–Ag coordination was scarcely found in Al₈₆Ni₇Y₆Ag₁, but a medium-range order between 7.5 and 9 Å was observed. The enhanced glass-forming ability and thermal stability of the alloy compared with Al₈₆Ni₈Y₆ can be attributed to the medium-range order of the Ag–Ag correlation. A second Ag–Ag coordination occurs in Al₈₆Ni₆Y₆Ag₂ and results in a decrease in glass-forming ability. The inter-atomic distances between all constituting elements increase during cooling. This increase is ascribed to a change in distribution of clusters around Al atoms towards clusters with higher coordination number around Al.