Internal stress and its effect on mechanical strength of metallic glass nanowires

Size induced strength increase in crystalline nanowires is related to crystal defects at small length scales. But how this phenomenon manifests in metallic glasses, an amorphous solid without obvious intrinsic structural defects, still remains an open issue. Here we show that in the amorphous nanowires free of obvious structural defects or cracks, reduction in wire diameter generally leads to weakening of the strength compared to the bulk sample. Our analysis shows that the surface stress as well as surface induced internal stress that scales inversely with the wire diameter become significant. It is the complex interplay between the applied stress and the internal residual stresses induced by the nanoscale surface that affects the mechanical behavior in the amorphous nanowires at the small length scale regime. The role of the localized shear banding played in relation to the size effect is also discussed in the context of the deformation mechanisms in amorphous wires with different sizes.