Structural mechanisms of the microalloying-induced high glass-forming abilities in metallic glasses

• Atomic-packing efficiency in major clusters increases when minor Ag is added.
• Structural regularity of major clusters increases when minor Ag is added.
• Minor Ag doping avoids the direct bonding between solute atoms.
• Excessive Ad addition leads to direct bonding between solute atoms.
• The factors deduced above contribute to the enhanced glass-forming ability.

The issue, doping-induced high glass-forming abilities (GFAs) in metallic glasses (MGs), has been investigated by systematic experimental measurements coupled with theoretical calculations in the ZrCuAgAl quaternary alloys. It is found that minor Ag addition leads to a high fraction of Ag-centered icosahedral like local structures, as well as enhanced atomic-packing efficiency and structural regularity in Zr- and Cu-centered major clusters. This can stabilize the amorphous structure and the GFA is accordingly enhanced. However, these structural factors have smaller values when excessive Ag atoms are added, leading to a deteriorated GFA. The present work provides an understanding of GFAs in multicomponent alloys and will shed light on the development of more MGs with high GFAs.