Localized shear deformation and fracture in a Zr-based bulk metallic glass

Behaviors of fracture and deformation in a Zr-Al-Ni-Cu bulk metallic glass(BMG) was investigated by using three-point bending tests. Apparent fracture toughness obtained by bending test was 40MPam(1/2) which is comparable to the value of ductile crystalline metals. This high toughness of the BMG should be understood by the crack-tip plasticity as well as crystalline metals. It is well known that plastic deformation occurs very inhomogeneously when BMGs are deformed at room temperature. Such inhomogeneity is manifested by the appearance of surface steps caused by localized shear deformation. In the present study, the surface steps due to the localized shear bands near a fracture surface have been examined in detail by using SEM and AFM, where much attention has been paid on the variation of the surface step height measured along the localized shear band. The variation of the step height indicates the gradient of plastic shear deformation, and it can be understood, in principle, as the introduction of elastic singularities corresponding dislocations in the case of crystalline materials.