Effect of shear-band formation and structural relaxation on mechanical properties of an Al-based metallic glass

The effect of cold rolling on the mechanical behavior of amorphous Al$_{86.8}$Ni$_{3.7}$Y$_{9.5}$ has been investigated by nanoindentation. This alloy does not crystallize in response to plastic deformation at room temperature. While significant pile-ups are observed around indentations in the as-spun alloy, they are small in the rolled sample. It is also found that rolling reduces the hardness. Deformation of the as-spun alloy occurs by nucleation and propagation of shear bands, whereas the cold-rolled alloy deforms by propagation of pre- existing shear bands. Annealing leads to a recovery of the pile-ups, with the hardness increasing to above its value for the as-spun sample. Using high-resolution transmission electron microscopy, nanovoids are observed to be uniformly distributed in the shear bands formed due to rolling. Annealing does not appear to affect these nanovoids. This work was funded by the National Science Foundation, Grant DMR-0314214