Relating Dynamic Properties to Atomic Structure in Metallic Glasses

H W Sheng,M J Kramer,E Ma

doi:10.1007/s11837-012-0360-y

Abstract

Atomic packing in metallic glasses is not completely random but displays various degrees of structural ordering. While it is believed that local structures profoundly affect the properties of glasses, a fundamental understanding of the structure–property relationship has been lacking. In this article, we provide a microscopic picture to uncover the intricate interplay between structural defects and dynamic properties of metallic glasses, from the perspective of computational modeling. Computational methodologies for such realistic modeling are introduced. Exploiting the concept of quasi-equivalent cluster packing, we quantify the structural ordering of a prototype metallic glass during its formation process, with a new focus on geometric measures of subatomic “voids.” Atomic sites connected with the voids are found to be crucial in terms of understanding the dynamic, including vibrational and atomic transport, properties. Normal mode analysis is performed to reveal the structural origin of the anomalous boson peak (BP) in the vibration spectrum of the glass, and its correlation with atomic packing cavities. Through transition-state search on the energy landscape of the system, such structural disorder is found to be a facilitating factor for atomic diffusion, with diffusion energy barriers and diffusion pathways significantly varying with the degree of structural relaxation/ordering. The implications of structural defects for the mechanical properties of metallic glasses are also discussed.

Highlights

When metallic liquids are cooled, atoms gradually lose their kinetic energy and their motion becomes increasingly sluggish as the temperature decreases
We revealed how vibrational and atomic transport properties are related to structural defects
For the vibrational properties of this glass, a microscopic picture was provided to interpret the origin of the anomalous boson peak (BP) in the vibration spectrum

Summary

INTRODUCTION

When metallic liquids are cooled, atoms gradually lose their kinetic energy and their motion becomes increasingly sluggish as the temperature decreases. While the theory of atomic-level shear stresses was intended to account for topology distortions, its effectiveness for binary systems has yet to be demonstrated.[47,48,49,50] the quantification of voids as structural defects in amorphous solids provides a microscopic picture to better understand the structure of glasses, and serves as a useful vehicle to unravel the structure–property relationships of MGs. Vibrational properties of metallic glasses are fundamental perperties[109] that are directly connected to the thermodynamics and kinetics of MGs; For example, the normal mode vibrational density of states (VDOS) g(x) affects barrier crossing rates on the potential energy landscape,[110] and enters Zwanzig’s models[111] for self-diffusion of liquids and solids.

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Findings

CONCLUSIONS