Pronounced β-relaxation in plastic FeNi-based bulk metallic glasses and its structural origin

Fe-based bulk metallic glasses (BMGs) usually exhibit brittle behavior and unconspicuous β-relaxation in their dynamic mechanical spectroscopy. We report a distinct β-relaxation behavior in FeNi-based BMGs with excellent plasticity. The origin of pronounced β-relaxation and plastic behaviors for the FeNi-based BMGs were investigated by synchrotron X-ray diffraction and nanoindentation tests in detail. It is found that the structural heterogeneity plays a key role in the dynamic of the FeNi-based BMGs, leading to large amount of loosely packed regions. The pronounced β-relaxation is also found to have a good correlation with the plasticity for the FeNi-based BMGs. This study might provide guidance for us to develop plastic BMGs from an atomic structural and glass dynamic perspective.