Brittle to ductile transition of metallic glasses induced by embedding spherical nanovoids.

The lack of global plasticity at low temperature seriously limits the application of metallic glasses (MGs) as structural materials. An approach to enhance the MG-ductility by dispersed spherical nanovoids is suggested and validated by molecular dynamics in the present paper. By introducing these nanovoids, a deformation mode transition from localized shear banding to homogeneous flow occurs. The ratio of void-surface area to MG volume λ is revealed to be the dominant factor controlling this brittle-to-ductile transition. Generally, for a given void volume fraction, smaller nanovoids with larger λ have better toughening effects. It is also discovered that the ductile responses of porous MGs with embedded nanovoids remain unchanged, even after several cycles of tensilecompressive loads. The intrinsic mechanism may be the transition of energetic void-surface atoms into internal atoms with lower potential energy. This process induces many uniformly distributed potential nucleation sites for shear transformation zones or embryonic shear bands (SBs), and thus provides another homogenous way to release the stored strain energy in MGs rather than by the formation of a single dominant SB. As a consequence, the highly localized deformation mode of classical MGs can be avoided. In addition, the effect of free and periodical boundary conditions and random distribution of nanovoids on the brittle-to-ductile transition are also discussed. The results may shed a light on the fabrication of better ductile MG materials. [ABSTRACT FROM AUTHOR]