Microplasticity in metallic glasses
type: CreativeWork
description: Metallic Glasses (MGs) are amorphous metallic alloys with exceptional mechanical and physical properties. Like all good things, this class of materials comes with its own problems, in this case (i) a lack of ductility, (ii) degradation in properties over time due to aging, and (iii) abrupt and unpredictable failure. In the past five decades since their discovery, the primary focus related to their mechanical properties has been the structural changes due to plasticity accumulating beyond macroscopic yielding. In contrast, the pre-yield regime has essentially been neglected, only now receiving increased attention due to the realization that potential pre-yield microplastic activity can have substantial effects on both structure and properties. This realization stems from indirect property measurements that reveal large changes in, for example, stored excess enthalpy after mechanical stresses of only a percent of the yield stress. The underlying structural activity and processes, that drive such strong structural evolution under a small far-field bias, remain unclear. To this end, the dissertation aims to probe structural processes taking place in the nominally elastic regime, thereby classifying this structural activity as microplasticity. Linked to the identified structural probing techniques, the microplastic regime is divided up into two parts, a stress range far below yielding, and stresses just prior to macroscopic strain localization and therefore shear banding. We use a coherent x-ray scattering technique (x-ray photon correlation spectroscopy or XPCS) to probe the lower stress range, whereas an in-situ acoustic emission (AE) technique is used to track structural activity close to yielding. As a first experiment, XPCS has been used to probe the atomic dynamics underlying microplasticity in an MG loaded under nominally elastic stresses using a four-point bending geometry. The key findings of this work are that i) relaxation times become increasingly longer with…
abstract: Metallic Glasses (MGs) are amorphous metallic alloys with exceptional mechanical and physical properties. Like all good things, this class of materials comes with its own problems, in this case (i) a lack of ductility, (ii) degradation in properties over time due to aging, and (iii) abrupt and unpredictable failure. In the past five decades since their discovery, the primary focus related to their mechanical properties has been the structural changes due to plasticity accumulating beyond macroscopic yielding. In contrast, the pre-yield regime has essentially been neglected, only now receiving increased attention due to the realization that potential pre-yield microplastic activity can have substantial effects on both structure and properties. This realization stems from indirect property measurements that reveal large changes in, for example, stored excess enthalpy after mechanical stresses of only a percent of the yield stress. The underlying structural activity and processes, that drive such strong structural evolution under a small far-field bias, remain unclear. To this end, the dissertation aims to probe structural processes taking place in the nominally elastic regime, thereby classifying this structural activity as microplasticity. Linked to the identified structural probing techniques, the microplastic regime is divided up into two parts, a stress range far below yielding, and stresses just prior to macroscopic strain localization and therefore shear banding. We use a coherent x-ray scattering technique (x-ray photon correlation spectroscopy or XPCS) to probe the lower stress range, whereas an in-situ acoustic emission (AE) technique is used to track structural activity close to yielding. As a first experiment, XPCS has been used to probe the atomic dynamics underlying microplasticity in an MG loaded under nominally elastic stresses using a four-point bending geometry. The key findings of this work are that i) relaxation times become increasingly longer with…
author: Das, Amlan
language: en
keywords: Microplasticity, Metallic Glasses, Dynamics, Mechanical Properties, XPCS, Acoustic Emission
date published: 2021-09-17T04:04:38Z
date modified: 2026-07-22T22:24:52Z
provider: University of Illinois - Urbana-Champaign
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Illinois at Urbana-Champaign

PropertyValue
property ID: Handle
value: http://hdl.handle.net/2142/110835