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| Author | : Soumya Swayamjyoti |
| Publisher | : |
| Total Pages | : |
| Release | : 2016 |
| Genre | : |
| ISBN | : |
| Author | : Jincheng Du |
| Publisher | : John Wiley & Sons |
| Total Pages | : 564 |
| Release | : 2022-03-29 |
| Genre | : Technology & Engineering |
| ISBN | : 1118940245 |
A complete reference to computer simulations of inorganic glass materials In Atomistic Simulations of Glasses: Fundamentals and Applications, a team of distinguished researchers and active practitioners delivers a comprehensive review of the fundamentals and practical applications of atomistic simulations of inorganic glasses. The book offers concise discussions of classical, first principles, Monte Carlo, and other simulation methods, together with structural analysis techniques and property calculation methods for the models of glass generated from these atomistic simulations, before moving on to practical examples of the application of atomistic simulations in the research of several glass systems. The authors describe simulations of silica, silicate, aluminosilicate, borosilicate, phosphate, halide and oxyhalide glasses with up-to-date information and explore the challenges faced by researchers when dealing with these systems. Both classical and ab initio methods are examined and comparison with experimental structural and property data provided. Simulations of glass surfaces and surface-water reactions are also covered. Atomistic Simulations of Glasses includes multiple case studies and addresses a variety of applications of simulation, from elucidating the structure and properties of glasses for optical, electronic, architecture applications to high technology fields such as flat panel displays, nuclear waste disposal, and biomedicine. The book also includes: A thorough introduction to the fundamentals of atomistic simulations, including classical, ab initio, Reverse Monte Carlo simulation and topological constraint theory methods Important ingredients for simulations such as interatomic potential development, structural analysis methods, and property calculations are covered Comprehensive explorations of the applications of atomistic simulations in glass research, including the history of atomistic simulations of glasses Practical discussions of rare earth and transition metal-containing glasses, as well as halide and oxyhalide glasses In-depth examinations of glass surfaces and silicate glass-water interactions Perfect for glass, ceramic, and materials scientists and engineers, as well as physical, inorganic, and computational chemists, Atomistic Simulations of Glasses: Fundamentals and Applications is also an ideal resource for condensed matter and solid-state physicists, mechanical and civil engineers, and those working with bioactive glasses. Graduate students, postdocs, senior undergraduate students, and others who intend to enter the field of simulations of glasses would also find the book highly valuable.
| Author | : Mohit Kumar |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2016 |
| Genre | : |
| ISBN | : |
The unique set of mechanical and magnetic properties possessed by metallic glasses has attracted a lot of recent scientific and technological interest. The development of new metallic glass alloys with improved manufacturability, enhanced properties and higher ductility relies on the fundamental understanding of the interconnections between their atomic structure, glass forming ability (GFA), transport properties, and elastic and plastic deformation mechanisms. This thesis is focused on finding these atomic structure-property relationships in Cu-Zr BMGs using molecular dynamics simulations. In the first study described herein, molecular dynamics simulations of the rapid solidification process over the Cu-Zr compositional domain were conducted to explore inter-dependencies of atomic transport and fragility, elasticity and structural ordering, and GFA. The second study investigated the atomic origins of serration events, which is the characteristic plastic deformation behaviour in BMGs. The combined results of this work suggest that GFA and ductility of metallic glasses could be compositionally tuned.
| Author | : Akihiko Hirata |
| Publisher | : Springer |
| Total Pages | : 79 |
| Release | : 2016-04-05 |
| Genre | : Mathematics |
| ISBN | : 4431560564 |
This book introduces the application of computational homology for structural analysis of metallic glasses. Metallic glasses, relatively new materials in the field of metals, are the next-generation structural and functional materials owing to their excellent properties. To understand their properties and to develop novel metallic glass materials, it is necessary to uncover their atomic structures which have no periodicity, unlike crystals. Although many experimental and simulation studies have been performed to reveal the structures, it is extremely difficult to perceive a relationship between structures and properties without an appropriate point of view, or language. The purpose here is to show how a new approach using computational homology gives a useful insight into the interpretation of atomic structures. It is noted that computational homology has rapidly developed and is now widely applied for various data analyses. The book begins with a brief basic survey of metallic glasses and computational homology, then goes on to the detailed procedures and interpretation of computational homology analysis for metallic glasses. Understandable and readable information for both materials scientists and mathematicians is also provided.
| Author | : Pei Zhang |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2018 |
| Genre | : |
| ISBN | : |
We studied the atomic scale structure of bulk metallic glass (BMG) with the combination of fluctuation electron microscopy (FEM) and hybrid reverse Monte Carlo (HRMC) simulation. Medium range order (MRO), which occupies the length scale between short range order (SRO) and long-range order, plays an important role on the properties of metallic glass, but the characterization of MRO in experiment is difficult because conventional techniques are not sensitive to the structure at MRO scale. Compared with the X-ray and neutron which can measure SRO by two-body correlation functions, FEM is an effective way to detect MRO structure through three and four-body correlation functions, providing information about the size, distribution, and internal structure of MRO combing HRMC modeling. Thickness estimation is necessary in FEM experiment and HRMC calculation, so in Chapter 3, we measured the elastic and inelastic mean free paths of metallic glass alloys based on focused ion beam prepared thin samples with measured thickness gradients. We developed a model based on the Wentzel atomic model to predict the elastic mean free path for other amorphous materials. In Chapter 4, we studied the correlation of MRO and glass forming ability ZrCuAl alloy. Results from Variable resolution fluctuation microscopy show that in Zr50Cu35Al15 the crystal-like clusters shrink but become more ordered, while icosahedral-like clusters grow. Compared with Zr50Cu45Al5, Zr50Cu35Al15 with poorer glass forming ability exhibits more stable crystal-like structure under annealing, indicating that destabilizing crystal-like structures is important to achieve better glass forming ability in this alloy. In Chapter 5, we studied the crystallization and MRO structural in deformed and quenched Ni60Nb40 metallic glass. The deformed Ni60Nb40 contains fewer icosahedral-like Voronoi clusters and more crystal-like and bcc-like Voronoi clusters. The crystal-like and bcc-like medium range order clusters may be the structural origin for its lower crystallization temperature compared with quenched alloy. Dynamics heterogeneity is proposed to be the microscopic origin of the dynamic nature of glass transition. Some experimental evidence and simulation have indicated that different regions of materials indeed relax at fast or slow rate. However, the spatial distribution of relaxation time visualized from the experiment as the direct evidence of heterogeneous dynamics is still challenging. We proposed to measure the structural dynamics of supercooled metallic glasses with electron correlation microscopy (ECM) technique at the nanometer scale. ECM was developed as a way to measure structural relaxation times of liquids with nanometer-scale spatial resolution using the coherent electron scattering equivalent of photon correlation spectroscopy. In chapter 6, we studied the experimental requirements of ECM to obtain reliable results. For example, the trajectory length must be at least 40 times the relaxation time to obtain a well-converged g2(t), and the time per frame must be less than 0.1 time the relaxation time to obtain sufficient sampling. ECM experiment was firstly realized in scanning transmission electron microscopy (STEM) mode and applied to measure the structural relaxation time of Pd based metallic glass. In order to overcome the drift problem and capture the spatial information, we developed ECM experiment in dark field (DF) mode. In Chapter 7, through DF-ECM, we visualized the spatially heterogeneous dynamics by in-situ heating Pt57.5Cu14.7Ni5.3P22.5 nanowire into supercooled liquid state, and quantify the size of the heterogeneity by four-point correlation function. The thickness effect and temporal evolution of the heterogeneous domain were also discussed. Additionally, a fast near-surface dynamics was discovered, providing an effective mechanism for surface crystallization of liquids by homogeneous nucleation.
| Author | : Juan Wang (Mechanical engineer) |
| Publisher | : |
| Total Pages | : 117 |
| Release | : 2018 |
| Genre | : Electronic dissertations |
| ISBN | : |
Despite intense interest, identifying the structural origin of glass forming ability in metallic alloys remains a challenge due to the difficulty of describing the evolution of the long-range disordered structure from the liquid. In this thesis, we integrate high-throughput experimental methods with computational simulations to study glass formation and the resulting mechanical properties, with a primary focus on the Al-Ni-Zr system. Based on our investigation of the structural and cluster evolution using molecular dynamics simulations, we report the variance of the fraction of different types of atomic clusters in the liquid as a potential parameter to predict glass formation. The predictive power of the variance in the liquid state was verified by comparison with alloy libraries synthesized by a highly efficient laser deposition technique. Experimentally, glass formation was found over a wide compositional range centered on Al21.4Ni23.9Zr54.7, which is in excellent agreement with the simulations. Because the variance of cluster fractions at temperatures above the crystallization temperature is independent of quench rate as well as any particular cluster type, we believe this method could be extended to any alloy system, including those of higher complexity.Building upon this work, we examine the fundamental factors that determine the distribution and volume fraction of the crystal nucleation in simulated Al20Ni60Zr20 metallic glass/crystalline composites. The results show that the initial distribution of the atoms does not contribute to the final faction of atoms that form BCC-coordinated crystals in the composite. However, one major factor that affects the crystalline fraction is the temperature at which the stable nuclei form. The stability of Al-centered 0, 3, 6, 4 clusters also plays an important role in the final percentage of the ordered atoms.Finally, nanoindentation was performed to identify trends in hardness and indentation modulus with composition. The relationship between cluster structure and the observed mechanical behavior was evaluated by molecular dynamic simulation in Al-Ni-Zr system. By addressing the local mechanical property-cluster structure-glass forming ability relationship in this system, this study expands the understanding of the relationship of atomic structure, macroscopic mechanical behavior and glass forming ability.
| Author | : Debaditya Chatterjee |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2023 |
| Genre | : |
| ISBN | : |
Glassy states are commonly observed across metallic, organic, and ceramic materials. They exhibit unique mechanical, thermal, and electronic properties. Metallic glasses are stronger than regular metals while being as pliable as plastics, but their wide-spread technological adoption is hindered by our poor understanding of their atomic ordering. Organic glasses have applications ranging from electronics to pharmaceuticals. Glasses lack long-range order, and their properties are mediated by nano-scale ordering. Experimental characterization of glassy structures is incredibly challenging due to the awesome complexity of their nanostructures and a lack of characterization techniques that can probe the local ordering and structural relaxation processes with nanometer-scale spatial resolution. Characterization techniques based on transmission electron microscopy (TEM) probe the structure and dynamics of such systems with nanometer-scale spatial resolution. Structural studies on metallic and organic glasses using 4-dimensional scanning transmission electron microscopy (4D STEM) reveal varying length scales of ordering in these systems and their impact on physical properties, at unprecedented spatial resolution. Electron correlation microscopy (ECM) analysis on time-resolved in situ thermal annealed TEM data lets us study glassy dynamics and reveals spatially heterogeneous dynamics in the bulk and at the surface of metallic glass nanowires. The techniques developed, and the mechanisms of structural ordering and relaxation dynamics revealed in these investigations, have implications on the synthesis, processing, and characterization of glassy systems with controlled thermal, electronic and mechanical properties, including growth of ultrastable metallic glass phases and molecular glasses with tunable structural anisotropy for organic electronics applications, fabrication of glassy nanostructures by superplastic forming, and control of surface crystallization.
| Author | : Pawel Koziatek |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2014 |
| Genre | : |
| ISBN | : |
Amorphous materials are ubiquitous in everyday life. They comprise "hard" and"soft" glasses. Hard amorphous systems are usually seen as structure materials, with properties and use comparable to those of crystalline solids. Soft glasses are usually seen as complex fluids, described in terms of their rheological properties with the corresponding practical applications (concrete, paints, drilling mud, cosmetic gels, creams or foams, etc). Amorphous materials can either present a solid-like behaviour or flow depending on their mechanical load: all are yield-stress fluids. Their usage limits are often defined by the occurrence of shear-banding, an extreme form of localization seen in molecular glasses as well as in granular materials. There is now considerable evidence that they are consequences of the existence of a disordered structure at the level of the elementary constituents (atoms, particles,...). Studies of plasticity in amorphous solids, are still hampered by the lack of any identifiable defect responsible for the plastic response. It is now acknowledged that plasticity is the net result of local rearrangements, or "shear transformations", involving small clusters of (say a few tens of) particles. These rearrangements are thermally--activated and are ubiquitous processes in the structural relaxation and deformation of glasses at low temperatures. Unfortunately, they take place over timescales long compared to those accessible to direct Molecular Dynamics simulations. Some extremely promising new tools, however, are opening the route towards accelerated algorithms for the simulation of thermal systems. They are based on numerical methods developed over these last two decades to determine thermally activated transitions in atomic systems. Of particular interest here is the Activation-Relaxation Technique (ART), an eigenvector-following method that allows the identification of activated states and paths in the potential energy landscape of atomic systems. In this study, we will show that although an exhaustive search for saddle points in case of disordered solids is unfeasible (because of the exponential number of activated states), ART can identify enough saddles to build statistically relevant samples, from which stationary distributions can be computed. The purpose of this strictly numerical thesis was the prediction of thermally activated kinetics in glasses such as those encountered experimentally. The nature of such miscroscopic events occuring in disordered systems was studied both under mechanical stress and in ageing conditions. We investigate two quantities that describe thermally-activated events within the harmonic approximation of the transition state theory, i.e. activation energy and attempt frequency.Since in the definition of an attempt frequency the curvature of the initial minimum and the saddle point are present, we wanted to see if there was a relation between attempt frequencies and activation energies of a given event in two types of systems: metallic glasses and silica glasses. Such correlation had been observed before for a wide range of phenomena and is referred to as the Meyer-Neldel compensation rule. We also attempt to answer if the simple BKS potential without Ewald summation is able to reproduce polyamorphism observed in silica glasses subject to hydrostatic compression and characterized mainly in terms of coordination numbers. Apart from thermally activated processes, the structural analyses of metallic and silica glasses were performed. The short and medium range orders were characterized using two methods: Voronoi tesselations for metallic glasses, providing us information about near neighbor conformations, and in case of silica, statistics of ring distributions.
| Author | : E. Donth |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 433 |
| Release | : 2013-04-17 |
| Genre | : Science |
| ISBN | : 3662043653 |
Describes and interrelates the following processes: cooperative alpha processes in a cold liquid, structural relaxation in the glass near Tg, the Johari-Goldstein beta process, the Williams-Götze process in a warm liquid, fast nonactivated cage rattling and boson peak, and ultraslow Fischer modes.
| Author | : Olle Eriksson |
| Publisher | : Oxford University Press |
| Total Pages | : 265 |
| Release | : 2017 |
| Genre | : Science |
| ISBN | : 0198788665 |
Several large experimental facilities that focus on detection and probing magnetization dynamics have been realized in Europe, USA and Japan. This book covers theoretical and practical aspects of the vibrant and emerging research field of magnetization dynamics.
