Effects of residual stress in elastic regime on the surface formability of a Zr-based metallic glass

In order to study elastic stress effects on the surface deformability of BMGs, indentations with a Berkovich diamond pyramid were done on an artificially bent Zr-based metallic glass stripe (Vitreloy-1). Residual indentation marks formed with a peak load of 500 mN were observed with an atomic force microscope for 7 artificial stress steps. Significant pile-ups (or surface upheavals around indents) and shear bands were observed at low stress levels less than 244 MPa and disappeared with an increase of the tensile stress. From a 3D morphological viewpoint, the tensile stress in elastic regime is understood to be beneficial to the surface formability of the Zr-based BMG, because the tensile stress invokes deeper indentations with slight elastic recovery and reduces the irregular pile-ups with shear bands.