Nanoscale viscoelastic transition from solid-like to liquid-like enables ductile deformation in Fe-based metallic glass

The cooling rate during vitrification is critical for determining the mechanical properties of metallic glasses. However, the structural origin of the cooling rate effect on mechanical behaviors is unclear. In this work, a systematical investigation of the cooling rate effect on the deformation mode, shear band nucleation, and nanoscale heterogeneous structure was conducted in three Fe-based metallic glasses. The brittle to ductile deformation transition was observed when increasing the cooling rate. Meanwhile, the governing shear band nucleation site from high load site to low load site appears the synchronous transition. By studying the corresponding nanoscale heterogeneous structure, it was found that nanoscale viscoelastic transition from solid-like to liquid-like as increasing cooling rate enables ductile deformation. The current work not only reveals the nanoscale structural origin of the cooling rate effect on the deformation behaviors, but also provides a new route to design ductile metallic glasses by freezing more nanoscale liquid-like regions during cooling.