Atomic-scale homogeneous plastic flow beyond near-theoretical yield stress in a metallic glass

Abstract

The onset of yielding and the related atomic-scale plastic flow behavior of bulk metallic glasses at room temperature have not been fully understood due to the difficulty in performing the atomic-scale plastic deformation experiments needed to gain direct insight into the underlying fundamental deformation mechanisms. Here we overcome these limitations by combining a unique sample preparation method with atomic force microscopy-based indentation, which allows study of the yield stress, onset of yielding, and atomic-scale plastic flow of a platinum-based bulk metallic glass in volumes containing as little as approximately 1000 atoms. Yield stresses markedly higher than in conventional nanoindentation testing were observed, surpassing predictions from current models that relate yield stress to tested volumes; subsequent flow was then established to be homogeneous without exhibiting collective shear localization or loading rate dependence. Overall, variations in glass properties due to fluctuations of free volume are found to be much smaller than previously suggested.

Universal mechanical response of metallic glasses during strain-rate-dependent uniaxial compression

“…In particular, the stress-strain curves for εeng 10 8 s −1 agree with those obtained using athermal quasistatic compression. Serrations in the stress-strain relations have also been found in experimental studies of uniaxial compression and nanoindentation of BMGs at low strain rates [19,24]. The stress-strain curves become more continuous and the maximum stress is non-monotonic with increasing strain rate.…”

Size-dependent deformation behavior in nanosized amorphous metals suggesting transition from collective to individual atomic transport

“…The relaxation time exhibits a strong temperature dependence and is commonly described by the Vogel-Fulcher-Tamman (VFT) equation 5 . Microscopically, such homogenous viscous flow has been envisioned through a collective movement of atoms, which has been suggested to occur within flow units, also called shear transformation zones (STZs) 6 – 9 , although recent direct experimental evidence suggests atomic homogenous flow 10 .…”