Effect of pre-existing shear bands on mechanical properties and serration behaviors in bulk metallic glasses

Pre-existing (multiple) shear bands were introduced into the ductile Zr36 Co28 Al16 and Zr65 Ni16 Cu15 Al10 bulk metallic glasses (BMGs) through the lateral-deformation, respectively. It was found that the pre-exiting shear bands can further enhance the compressive plasticity of ductile BMGs. According to the serration analysis on the plastic deformation of the as-cast and the pre-deformed samples, the serration events in the stress-strain curves during deformation display a self-organized critical (SOC) behavior. Compared with the as-cast BMGs, a larger power-law scaling exponent calculated based on serrated flow behaviors becomes larger for the pre-deformed BMGs, implying that the shear banding stability of BMGs is effectively enhanced. This should be caused by the pronounced interactions of shear bands during plastic deformation for the pre-deformed BMGs. However, by introducing a large amount of multiple shear bands into the glassy matrix, it also becomes easier for shear bands to propagate along the pre-existing shear bands, leading to a lower cut-off elastic energy density for the pre-deformed BMGs. More multiple shear bands with stronger interactions for the pre-deformed BMGs could provide a larger chance to activate the shear-band cracking but less local elastic energies are remained for the subsequent crack-linking.