Origin of indentation size effect of hardness in Bulk Metallic Glasses

The work highlights that the indentation depth effect arises from the interplay between elasticity and plasticity, rather than being solely influenced by factors such as indentation depth, contact area, or indenter radius. From the creep analysis, we demonstrate that the size-dependent hardness originates from the microstructural changes indicated by the characteristic relaxation time. Besides, we show that the decrease in indentation hardness is dominated by the increase in defect concentration, which is also closely related to the activation of shear transformation zones that control the plasticity of bulk metallic glasses. Furthermore, we elucidate the physical mechanisms behind the distinct indentation hardness at various depths from the perspective of defect concentration. Our work provides clarification for size-dependent hardness and deepen the understanding in deformation mechanism of BMGs. • The indentation size effect of hardness is observed in bulk metallic glasses. • The relationship between hardness, contact radius, and indentation depth has been established. • A universal scaling law was developed to assess the indentation hardness and yield strength. • The physical mechanisms behind the distinct indentation hardness have been elucidated.