Homogenization of plastic deformation in metallic glass foils less than one micrometer thick

Abstract

Metallic glasses do not possess crystalline structures with slip systems that provide for plastic deformation via dislocation glide. As such, when put under applied stress, they show a wide reversible elastic deformation ${\ensuremath{\epsilon}}_{\text{el}}\ensuremath{\approx}2\mathrm{%}$ before plastic flow occurs heterogeneously by localization in shear bands only tens of nanometers in thickness. Very recently, there have been reports that in microscopic (submicron thickness) pillars, such shear bands no longer form and deformation occurs homogeneously. Here we report on plastic deformation of submicron thickness foils of metallic glasses. When such foils are compressed or notched, a similar transition occurs from the usual heterogeneous plastic deformation mode via shear banding to more homogeneous deformation without formation of shear bands. Some shape instabilities in the form of vortices observed at interfaces between plastic zones and nondeformed regions are consistent with sharp deformation-induced density, velocity, and viscosity gradients. The onset of homogeneous deformation in the microscopic regime is discussed in relation to shear-band formation energy and thickness.