Shear Bands Topology in the Deformed Bulk Metallic Glasses

Mikhail Seleznev,Alexei Vinogradov

doi:10.3390/met10030374

Mikhail Seleznev, Alexei Vinogradov

Open Access

https://doi.org/10.3390/met10030374

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Abstract

Recent experimental studies revealed the presence of Volterra dislocation-type long-range elastic strain/stress field around a shear band (SB) terminated in a bulk metallic glass (BMG). The corollary from this finding is that shear bands can interact with these stress fields. In other words, the mutual behaviour of SBs should be affected by their stress fields superimposed with the external stresses. In order to verify this suggestion, the topography of the regions surrounding SBs terminated in the BMGs was carefully analysed. The surfaces of several BMGs, deformed by compression and indentation, were investigated with a high spatial resolution by means of scanning white-light interferometry (SWLI). Along with the evidence for the interaction between SBs, different scenarios of the SB propagation have been observed. Specifically, the SB path deviation, mutual blocking, and deflection of SBs were revealed along with the significant differences between the topologies of the mode II (in-plane) and mode III (out of plane) SBs. While the type II shear manifests a linear propagation path and a monotonically increasing shear offset, the type III shear is associated with a curved, segmented path and a non-monotonically varying shear offset. The systematic application of the “classic” elastic Volterra’s theory of dislocations to the behaviour of SBs in BMGs provides new insight into the widely reported experimental phenomena concerning the SB morphology, which is further detailed in the present work.

Highlights

Bulk metallic glasses (BMGs) possess a unique set of properties such as an unrivalled combination of toughness and strength [1], very high elastic limit and elastic energy capacity [2], biocompatibility [3], corrosion resistance, etc. [4]
Measurement of the Long-Range Stress Fields Produced by Shear Bands
The first brief report on the direct observations of the long-range elastic strain and stress fields created by a shear band terminated inside the BMG was made by the same authors in Reference [26]

Summary

Introduction

Bulk metallic glasses (BMGs) possess a unique set of properties such as an unrivalled combination of toughness and strength [1], very high elastic limit and elastic energy capacity [2], biocompatibility [3], corrosion resistance, etc. [4]. One of the main disadvantages is the localisation of the BMG plastic deformation at room temperature in the shear bands (SB) [5]. SB is a planar defect with a thickness of about 10–20 nm [6] accumulating the excess-free volume (EFV) during deformation [7]. Such a “decompaction” of the SB structure induces strain softening [8], with the formation of voids and microcracks merging into the main crack as load increases [9,10]. Significant experimental evidence has been put forward on strain hardening and material densification occurring in BMGs in association with shear bands during mechanical compression [11], tension [12], and rolling [13].

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