Structural Signature of Plasticity Unveiled by Nano-Scale Viscoelastic Contact in a Metallic Glass.

Y M Lu,M X Pan,C T Liu,J J Bladin,S Wang,Y Yang,B A Sun,J F Zeng,Q Wang,S Gravier,J Lu,W H Wang

doi:10.1038/srep29357

Abstract

Room-temperature plasticity in metallic glasses (MGs) is commonly associated with local structural heterogeneity; however, direct observation of the subtle structural change caused by plasticity is vitally important but the data are extremely scarce. Based on dynamic atomic force microscopy (DAFM), here we show that plasticity-induced structural evolution in a Zr-Ni MG can be revealed via nano-scale viscoelastic contacts between an AFM tip and plastically deformed MG surface layers. Our experimental results clearly show a spatial amplification of the nano-scale structural heterogeneity caused by the distributed plastic flow, which can be linked to the limited growth, reorientation and agglomeration of some nano-scale energy-absorbing regions, which are reminiscent of the behavior of the defect-like regions with non-affine deformation as conceived in many theories and models. Furthermore, we are able to experimentally extract the thermodynamic properties of these nano-scale regions, which possess an energy barrier of 0.3–0.5 eV, about half of that for a typical shear transformation event that usually occurs at the onset of plasticity. The outcome of our current work sheds quantitative insights into the correlation between plasticity and structural heterogeneity in MGs.

Highlights

In principle, the amorphous structure of a glassy solid is inherited from the corresponding supercooled liquid after glass transition
To directly unveil the dynamic heterogeneity in metallic glasses (MGs), it was first demonstrated by Liu et al.[40] that dynamic atomic force microscopy (DAFM) with amplitude-modulation could be utilized as an effective tool
A thin-film metallic glass (TFMG) with the composition of Zr70Ni30 was prepared by magnetron sputtering

Summary

Introduction

The amorphous structure of a glassy solid is inherited from the corresponding supercooled liquid after glass transition. The structure of the glassy solids vitrified from fragile liquids tends to be heterogeneous in a dynamic sense, containing “liquid-like” regions with short relaxation times as embedded into “solid-like” regions with long relaxation times. This view of dynamic heterogeneity is validated for MGs with the recent results obtained from a variety of simulations[27,30,35]. The AFM images depend on the structure of a MG and the size of the interaction volume In such a case, a micromechanical model is needed to relate the viscoelastic response of a MG under AFM tapping to its dynamic heterogeneity. Our goal is to use the DAFM method to probe the plasticity-induced structural evolution in MGs and develop a micromechanical model to understand the results in a more quantitative manner

Objectives

Methods

Results

Conclusion