A comparison of in- and ex situ generated shear bands in metallic glass by transmission electron microscopy

TL;DR

This study compares shear bands in metallic glass formed during in situ tensile tests and ex situ cold rolling using transmission electron microscopy, revealing differences in their formation, structure, and development stages.

Contribution

It provides a detailed comparison of shear bands in metallic glass from in situ and ex situ processes, highlighting their distinct features and formation mechanisms.

Findings

In situ shear bands show spearhead-like fronts and no shear steps.

Ex situ shear bands display alternating density changes and shear offsets.

Shear band initiation, propagation, and arrest occur at different stages in both methods.

Abstract

Shear bands originating from in situ tensile tests of Al$_{88}$Y$_{7}$Fe$_{5}$ melt-spun ribbons conducted in a transmission electron microscope are compared with ones which had formed ex situ during cold rolling. During in situ straining, the observations of a spearhead-like shear front, a meniscus-like foil thickness reduction and no apparent shear steps to accommodate strain suggest shear band initiation by a rejuvenating shear front followed by shearing along the already softened paths. This leads to necking and subsequent failure under the reduced constraint of a 2D geometry in the thin foil and thus explains the observed lack of ductility under tension. In contrast, shear bands formed during cold rolling display distinct alternating density changes and shear off-sets. An explanation for this difference may be that in situ shear bands rip before such features could develop. Moreover, both in and ex situ experiments suggest that initiation, propagation and arrest of shear bands occur during different stages.