Brink, Tobias (2017)
Heterogeneities in Metallic Glasses: Atomistic Computer Simulations on the Structure and Mechanical Properties of Copper–Zirconium Alloys and Composites.
Technische Universität Darmstadt
Ph.D. Thesis, Primary publication
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Item Type: | Ph.D. Thesis | ||||
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Type of entry: | Primary publication | ||||
Title: | Heterogeneities in Metallic Glasses: Atomistic Computer Simulations on the Structure and Mechanical Properties of Copper–Zirconium Alloys and Composites | ||||
Language: | English | ||||
Referees: | Albe, Prof. Dr. Karsten ; Eckert, Prof. Dr. Jürgen | ||||
Date: | 2017 | ||||
Place of Publication: | Darmstadt | ||||
Date of oral examination: | 7 December 2016 | ||||
Abstract: | The present thesis deals with molecular dynamics computer simulations of heterogeneities in copper–zirconium metallic glasses, ranging from intrinsic structural fluctuations to crystalline secondary phases. These heterogeneities define, on a microscopic scale, the properties of the glass, and an understanding of their nature and behaviour is required for deriving the proper structure–property relations. In terms of composite systems, we start with the amorphisation of copper nanolayers embedded in a metallic glass matrix. While copper is an fcc metal with a high propensity for crystallisation, amorphisation can in fact occur in such systems for thermodynamic reasons. This is due to interface effects, which are also known from heterogeneous interfaces in crystals or from grain boundary complexions, although in absence of lattice mismatch. In single-phase glasses, intrinsic heterogeneities are often discussed in terms of soft spots or geometrically unfavourable motifs (GUMs), which can be considered to be mechanically weaker, defective regions of the glass. We investigate the relation between these motifs and the boson peak, an anomaly in the vibrational spectrum of all glasses. We demonstrate a relation between the boson peak and soft spots by analysing various amorphous and partially amorphous samples as well as high-entropy alloys. Finally, we treat the plastic deformation of glasses, with and without crystalline secondary phases. We propose an explanation for the experimentally observed variations of propagation direction, composition, and density along a shear band. These variations of propagation direction are small in the case of single-phase glasses. A considerably greater influence on shear band propagation can be exerted by precipitates. We systematically investigate composites ranging from low crystalline volume fraction up to systems which resemble a nanocrystalline metal. In this context, we derive a mechanism map for composite systems and observe the breakdown of these mechanisms with increasing crystalline volume fraction during the transition towards the nanocrystalline state. |
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Uncontrolled Keywords: | metallic glasses, shear bands, molecular dynamics, mechanical properties, copper, zirconium, crystalline precipitates, boson peak, solid-state amorphisation | ||||
URN: | urn:nbn:de:tuda-tuprints-58586 | ||||
Classification DDC: | 500 Science and mathematics > 530 Physics | ||||
Divisions: | 11 Department of Materials and Earth Sciences > Material Science 11 Department of Materials and Earth Sciences > Material Science > Materials Modelling |
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Date Deposited: | 17 Jan 2017 13:04 | ||||
Last Modified: | 28 Jul 2020 11:30 | ||||
URI: | https://tuprints.ulb.tu-darmstadt.de/id/eprint/5858 | ||||
PPN: | 398582149 | ||||
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