Free volume: An indicator of the glass-forming ability in binary alloys

As a specific concept, free volume is proposed to affect the glass formation in alloys, while such issue remains unsolved, because free volume itself is ambiguous and elusive. In this work, the correlation between the free volume and the glass-forming ability (GFA) in some binary alloy systems has been investigated by a series of simulations combined with synchrotron-radiation based experiments. A new approach for detecting void spaces and even free volumes quantitatively in metallic glasses is developed, based on which we reveal that the size of free volumes significantly affects the glass formation. In particular, for ribbons with different compositions but the same thickness, a composition where there is a local maximum of GFA, there is a local bump of size value of free volumes, making it possible for free volumes to be an effective indicator of GFA. The present work provides new insight into the glass formation from free volume aspect, which can be helpful for understanding of both structure and properties in metallic glasses.