Liquid dynamics and glass formation of Gd55Co20Al25 metallic glass with minor Si addition

Liquid dynamics plays an essential role in glass formation. Here we observed a distinct change of liquid dynamics in Gd55Co20Al25 metallic glass induced by microalloying Si element. In the equilibrium melt, minor Si (0.5 at.%) addition leads to a more fragile liquid behavior and a smaller strength of liquid-liquid transition with the transition strength (ΔF) decreasing from 0.76 to 0.35. However, in the supercooled liquid, Si-doped liquid exhibits a remarkable enhanced fragile-to-strong transition (FST), and the value of FST factor f increases sharply from 1.63 to 3.84, resulting in a stronger liquid behavior and more sluggish crystallization kinetics for Gd55Co20Al24.5Si0.5 metallic glass. Moreover, minor Si addition promotes the formation of a crystal-like structure with a size of 1−2 nm. The interactions between the crystal-like structures and other local favored clusters frustrate the further growth of crystal-like phases, thus stabilizes the amorphous structure. As a result, the glass-forming ability (GFA) was largely improved. The critical diameter of Gd55Co20Al25 metallic glass increased from 2 to 7 mm with 0.5 at.% Si addition without deterioration of the magnetocaloric effect. This study provides valuable insight for understanding the distinct effect of microalloying on GFA of metallic glasses from the aspect of the evolution of the liquid.