Molecular dynamics simulation of intrinsic and extrinsic mechanical properties of amorphous metals

Mechanical response of amorphous metal Ni40Zr60 under applied tensile loading is investigated using large-scale atomistic simulations. To obtain intrinsic properties, homogeneous samples with atomically smooth surface are used while samples with deliberately introduced surface notches of varying depths and root radii are used to test extrinsic effects. It is found that the notch-free samples show strength close to the theoretical fracture strength and extremely large ductility. Apparent strain hardening and strain rate sensitivity are also observed in these studies. It is argued that the free volume generation and localized shear displacement are responsible for the mechanical properties. Therefore, the presence of surface imperfections can greatly reduce the strength and ductility. The results suggest that to retain and improve the intrinsic mechanical properties of amorphous metals, surface treatment may be needed, which has been practiced in oxide glass industry for centuries but received little attention in metallic glass community.