Uniform tensile elongation in framed submicron metallic glass specimen in the limit of suppressed shear banding

Metallic glasses (MGs) normally plastically deform via severe strain localization in the form of shear banding at room temperature. Here we show that, in the event of much delayed shear banding, submicron-scale MG specimens can elongate homogeneously in tension to a uniform plastic strain as large as 12% before failure, plus an estimated elastic strain of similar to 5%, at a temperature close to room temperature (below 70 degrees C). This high deformability of MGs well below the glass transition temperature, revealed in situ using tensile testing inside a transmission electron microscope and specimens prepared via focused ion beam micromachining, is attributed to the suppression of shear banding instability due to the nanoscale samples together with a sample frame design that imparts high effective machine stiffness and confinement. We also point out that the pronounced "homogeneous" deformation reported here is a form of non-localized deformation that is different from the homogeneous viscous flow for superplastic forming at high temperatures (in the supercooled liquid state), and from the intrinsic tensile ductility (stable uniform elongation) resulting from inherent strain hardening and strain-rate hardening mechanisms in free-standing conventional crystalline metals under uniaxial tension. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.