Sopu, Daniel (2011)
Molecular Dynamics Simulations of Metallic Nanoglasses.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
The prospect of realizing new bulk metallic glasses with improved properties has driven a large amount of research since the early work of Duwez [1]. In analogy to nanocrystalline solids, a new type of metallic glasses may by synthesized by consolidating glassy powder. This so-called nanoglass consists of glassy grains separated by interfaces [2]. So far, the existence of nanoglasses was only indirectly proven by experiments [2, 3, 4, 5]. This dissertation presents molecular dynamics simulations of nanoglasses and provides detailed insights into the structure and properties of this class of material. In the first part, an investigation of the structure and stability of a planar glass-glass interface is conducted by analyzing the local topology, alloy composition and density in comparison to the bulk structure. An analogy between an internal interface and a shear band is established. The stability of the glass-glass interfaces under thermal treatment and hydrostatic pressure is also analyzed. The second part is dedicated to the deformation behavior of metallic nanoglasses. Here, mechanical properties of a Cu64Zr36-nanoglass are characterized under tensile load and compared to the deformation behavior of a homogeneous bulk glass. For this study, dense and porous nanoglasses are used and the influence of grain size and porosity on the plastic behavior of nanoglasses is investigated. In addition, it is studied how thermal treatment and prior-deformation change the plastic response of the metallic nanoglass. In the third part, the phonon density of states (PDOS) of nanoglasses is studied in comparison to other nanostructures (nanoparticles, nanocrystals and embedded nanoparticles). In this case, germanium is used as representative reference material. By comparing with the PDOS of single crystalline and amorphous structures, the physical origins of additional or vanishing vibrational modes or frequency shift are identified. A general view on the interplay of nanostructural features and lattice vibrations is provided. In the last part, an investigation of the crystalline to amorphous transition of thin iron films embedded in AlFe glass is conducted. For the first time theoretical evidence is provided for the existence of a single-component metallic glass. The calculated PDOS reinforce the aforementioned statements. In addition, the investigation of finite size effects in PDOS is extended for the case of Fe thin films.
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2011 | ||||
Autor(en): | Sopu, Daniel | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Molecular Dynamics Simulations of Metallic Nanoglasses | ||||
Sprache: | Englisch | ||||
Referenten: | Karsten, Prof. Dr. Albe ; Hahn, Prof. Dr. Horst | ||||
Publikationsjahr: | 1 September 2011 | ||||
Datum der mündlichen Prüfung: | 25 November 2011 | ||||
URL / URN: | urn:nbn:de:tuda-tuprints-28453 | ||||
Kurzbeschreibung (Abstract): | The prospect of realizing new bulk metallic glasses with improved properties has driven a large amount of research since the early work of Duwez [1]. In analogy to nanocrystalline solids, a new type of metallic glasses may by synthesized by consolidating glassy powder. This so-called nanoglass consists of glassy grains separated by interfaces [2]. So far, the existence of nanoglasses was only indirectly proven by experiments [2, 3, 4, 5]. This dissertation presents molecular dynamics simulations of nanoglasses and provides detailed insights into the structure and properties of this class of material. In the first part, an investigation of the structure and stability of a planar glass-glass interface is conducted by analyzing the local topology, alloy composition and density in comparison to the bulk structure. An analogy between an internal interface and a shear band is established. The stability of the glass-glass interfaces under thermal treatment and hydrostatic pressure is also analyzed. The second part is dedicated to the deformation behavior of metallic nanoglasses. Here, mechanical properties of a Cu64Zr36-nanoglass are characterized under tensile load and compared to the deformation behavior of a homogeneous bulk glass. For this study, dense and porous nanoglasses are used and the influence of grain size and porosity on the plastic behavior of nanoglasses is investigated. In addition, it is studied how thermal treatment and prior-deformation change the plastic response of the metallic nanoglass. In the third part, the phonon density of states (PDOS) of nanoglasses is studied in comparison to other nanostructures (nanoparticles, nanocrystals and embedded nanoparticles). In this case, germanium is used as representative reference material. By comparing with the PDOS of single crystalline and amorphous structures, the physical origins of additional or vanishing vibrational modes or frequency shift are identified. A general view on the interplay of nanostructural features and lattice vibrations is provided. In the last part, an investigation of the crystalline to amorphous transition of thin iron films embedded in AlFe glass is conducted. For the first time theoretical evidence is provided for the existence of a single-component metallic glass. The calculated PDOS reinforce the aforementioned statements. In addition, the investigation of finite size effects in PDOS is extended for the case of Fe thin films. |
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Alternatives oder übersetztes Abstract: |
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Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 500 Naturwissenschaften und Mathematik > 500 Naturwissenschaften 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften |
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Fachbereich(e)/-gebiet(e): | 11 Fachbereich Material- und Geowissenschaften 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft > Fachgebiet Materialmodellierung |
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Hinterlegungsdatum: | 19 Dez 2011 09:26 | ||||
Letzte Änderung: | 05 Mär 2013 09:57 | ||||
PPN: | |||||
Referenten: | Karsten, Prof. Dr. Albe ; Hahn, Prof. Dr. Horst | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 25 November 2011 | ||||
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