Elastic Fluctuations and Structural Heterogeneities in Metallic Glasses

Abstract

Suppressing crystallization of a metallic melt results in a disordered solid, also known as a metallic glass. One may conclude that a metallic glass is free of defined structural length scales beyond some atomic-scale value that characterizes short-and medium-range order. While it is well known from atomistic modeling that a metallic glass is structurally heterogeneous, heterogeneities at such a small length scale can hardly be resolved in experiments. This review highlights experimental insights into elastic fluctuations and structural heterogeneities that emerge at scales between a few nanometers and tens to hundreds of micrometers. It distinguishes between structural and property fluctuations in as-cast metallic glasses, and heterogeneities introduced by elastic and inhomogeneous plastic deformation. As-cast glasses reveal elastic fluctuations across 3 orders of magnitude, suggesting a hierarchy of length scales that can be tuned by thermomechanical processing. Similarly, nanoscale strain localization into shear bands drives the formation of structural and elastic heterogeneities at both the nano-and the microscale. It is proposed that both types of fluctuations will allow one to quantitatively define structure-property relationships via measurable length scales-an approach that has largely contributed to the engineering success of crystalline metals.

Beyond Serrated Flow in Bulk Metallic Glasses: What Comes Next?

“…One obvious reason for this is the difficulty in revealing and characterizing a nano-scale sheared region in a disordered material. In the context of structural heterogeneities of metallic glasses, this has been summarized in detail in a recent review article, [61] and we will here only highlight a few aspects regarding the fluctuations of both length scales and structural measures of shear bands.…”

Potential energy states and mechanical properties of thermally cycled binary glasses

“…The design of novel strategies and optimization of thermal and mechanical treatments of metallic glasses is important for accessing a broad range of states with improved physical and mechanical properties [1]. It is generally accepted that an elementary plastic event in disordered solids involves a collective rearrangement of a small group of atoms or a shear transformation [2,3].…”

Measuring Structural Heterogeneities in Metallic Glasses Using Transmission Electron Microscopy

“…With tip sizes down to the nanometer scale, the tip-sample interaction can be analyzed in local regions to reveal the mechanical properties of the interaction volume. For example, elastic heterogeneity has been intensively studied in recent years [7] and found to occur on a length scale of <10 nm, in good agreement with TEM observations [9]. By measuring tip-sample contact-resonance frequencies with atomic force acoustic microscopy (AFAM), Wagner et al found heterogeneities in the local modulus of a PdCuSi MG which are much larger in magnitude than in its crystalline counterpart [8].…”

“…Beyond the feature of missing long-range order, the amorphous structure of MGs has been found to be heterogeneous rather than homogenous [5,6]. Both structure and mechanical properties have been found to be different in different regions of MGs on length scales ranging from the nanoscale to the microscale [7]. So far, heterogeneities have been found in the modulus [8], density [9,10], and relaxation behavior [11].…”