Stick-slip dynamics and recent insights into shear banding in metallic glasses
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ite extensive research, the understanding of the fundamental processes governing yielding and plastic flow in metallic glasses remains poor. This is due to experimental difficulties in capturing plastic flow as a result of a strong localization in space and time by the formation of shear bands at low homologous temperatures. Unveiling the mechanism of shear banding is hence key to developing a deeper understanding of plastic deformation in metallic glasses. We will compile recent progress in studying the dynamics of shear-band propagation from serrated flow curves. We will also take a perspective gleaned from stick-slip theory and show how the insights gained can be deployed to explain fundamental questions concerning the origin, mechanism, and characteristics of flow localization in metallic glasses.
I. INTRODUCTION
Since their discovery by Duwez and coworkers in 1960,1 metallic glasses have attracted considerable research interest on both a fundamental scientific and an engineering level. Because of their unique materials properties2 and spurred along by the significant progress in alloy development over the last few decades,3 metallic glasses have proved to be promising materials for both functional and structural applications,4 especially in bulk form. Owing to a complex, disordered atomic structure, however, the fundamental processes and mechanisms governing their properties remain in many cases poorly understood. This applies particularly to the field of mechanical properties, which has received broad attention in recent years.5–7 While some early attempts at clarification focused on transferring concepts of dislocation theory developed for crystalline metals to disordered media,8 it is now commonly understood that the nature and atomic-scale mechanisms of plastic flow in amorphous metals must be fundamentally different to their crystalline counterparts. Following from early work conducted by Argon9 as well as Spaepen et al.,10,11 a concept that has now gained increasing popularity is that of plasticity governed by shear-induced, local structural rearrangements of atomic clusters, so-called shear transformation zones (STZs).12 However, establishing experimental evidence for the validity of this atomic-scale flow model remains difficult, whereas, for example, at a much larger scale, analogous behavior of particle rearrangements can be captured in colloidal glasses.13 For metallic glasses, a)
Address all correspondence to this author. [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2011.178 J. Mater. Res., Vol. 26, No. 12, Jun 28, 2011
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additional experimental difficulties reside in a strong localization of plastic flow in both time and space, typically observed at low homologous temperatures at which shear banding prevails.11 Understanding the process of flow localization is hence crucial to unveiling the fundamental plastic flow mechanisms in metallic glasses. Flow localization in shear bands is most generally fo
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