Atomic-Scale Modeling of the Structure and Dynamics of Dislocations in Complex Alloys at High Temperatures PDF Download
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Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781721568062
Category :
Languages : en
Pages : 26
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Book Description
We report on the progress made during the first year of the project. Most of the progress at this point has been on the theoretical and computational side. Here are the highlights: (1) A new code, tailored for high-end desktop computing, now combines modern Accelerated Dynamics (AD) with the well-tested Embedded Atom Method (EAM); (2) The new Accelerated Dynamics allows the study of relatively slow, thermally-activated processes, such as diffusion, which are much too slow for traditional Molecular Dynamics; (3) We have benchmarked the new AD code on a rather simple and well-known process: vacancy diffusion in copper; and (4) We have begun application of the AD code to the diffusion of vacancies in ordered intermetallics. Daw, Murray S. and Mills, Michael J. Glenn Research Center NASA/CR-2003-212122, NAS 1.26:212122, E-13774
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781721568062
Category :
Languages : en
Pages : 26
Get Book Here
Book Description
We report on the progress made during the first year of the project. Most of the progress at this point has been on the theoretical and computational side. Here are the highlights: (1) A new code, tailored for high-end desktop computing, now combines modern Accelerated Dynamics (AD) with the well-tested Embedded Atom Method (EAM); (2) The new Accelerated Dynamics allows the study of relatively slow, thermally-activated processes, such as diffusion, which are much too slow for traditional Molecular Dynamics; (3) We have benchmarked the new AD code on a rather simple and well-known process: vacancy diffusion in copper; and (4) We have begun application of the AD code to the diffusion of vacancies in ordered intermetallics. Daw, Murray S. and Mills, Michael J. Glenn Research Center NASA/CR-2003-212122, NAS 1.26:212122, E-13774
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 12
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Author: Murray S. Daw
Publisher:
ISBN:
Category : Atomic structure
Languages : en
Pages :
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Author: United States. National Aeronautics and Space Administration
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Mulaine Shih
Publisher:
ISBN:
Category : Alloys
Languages : en
Pages : 0
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Mechanical behavior of crystalline materials is determined by crystal defects such as dislocations. Understanding the response of defects to forces is thus crucial to improve mechanical properties and to better design and engineer advanced structural materials. Motivated by metastable high entropy alloys (HEAs), we first study the dislocation behavior in a class of metastable fcc alloys. Transitioning from fcc to hcp stable phases in these alloys corresponds to a change from positive to negative average stacking fault energy (SFE). We perform Molecular Dynamics (MD) simulations, and use random NiCo alloys as the model metastable fcc alloy system. We show that the splitting distance between Shockley partial dislocations can remain finite even in a negative average SFE alloy, at finite temperatures. By investigating the effect of average versus “local” SFE on the dislocation stability, and examining the decorrelation force to break the two partial dislocations from equilibrium in these alloys, we are able to piece the puzzle together. We show that in concentrated alloys, the major resisting force is caused by the interaction of dislocations with local solute environments acting on partial dislocations. Next, we present our effort to predict the stress state of atomic-scale defects in experimental observations, captured by high resolution transmission electron microscopy (TEM) images. We propose a new method utilizing the continuum J-integral concept to compute the forces at atomic-scale. The new method is applied to example atomistic simulations of dislocation interactions, and results are validated with its theoretical Peach-Koehler force. Moreover, we investigate the potential origin of preferential deformation at thin deformation twins in CrCoNi alloys under cyclic loading. Assisted from atomistic simulations, we examine the local stress field at the twin boundary with free surfaces. Pure Cu was chosen as our model system for its chemical simplicity and having a similar anisotropy ratio to CrCoNi alloys. We demonstrate the effect of twin size on the strain localization. The high elastic anisotropy induces local stress concentration, which served as a crack initiation site under cyclic loading. We then extend the crack initiation model proposed by Neumann and Tonnessen to discuss the behavior in CrCoNi alloys. In summary, this thesis interrogates the possible deformation mechanisms in concentrated alloys and provides fundamental understanding of the dislocation behavior and offers insight for future alloy developments and applications.
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Category :
Languages : en
Pages : 0
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Intermetallic alloys are excellent materials for bridging the gap between atomic level processes and macroscopic properties, because the mechanical behavior of these alloys can be closely related to their dislocation structures. The research support by this grant, and described here, was undertaken to elucidate the relationship between atomic level dislocation core structures, alloy composition, and macroscopic mechanical behavior in a series of Nix, Fe(1-x)3Ge alloys and to develop the techniques necessary to perform microsample tensile tests of single crystalline intermetallic alloys. The results from this study, which are described below, have resulted in 6 journal articles, 5 conference proceedings, numerous conference presentations and two M.S. Dissertations. The dislocation structure observations provide benchmarks for first-principle electronic structure calculations and the availability of microsample testing allows for mesoscale testing of individual grains in a number of structural alloys. Both have proven to be valuable tools for bridging the length scales that govern the mechanical performance of high temperature structural materials.
Author: Sidney Yip
Publisher: Springer Science & Business Media
ISBN: 1402032862
Category : Science
Languages : en
Pages : 2903
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The first reference of its kind in the rapidly emerging field of computational approachs to materials research, this is a compendium of perspective-providing and topical articles written to inform students and non-specialists of the current status and capabilities of modelling and simulation. From the standpoint of methodology, the development follows a multiscale approach with emphasis on electronic-structure, atomistic, and mesoscale methods, as well as mathematical analysis and rate processes. Basic models are treated across traditional disciplines, not only in the discussion of methods but also in chapters on crystal defects, microstructure, fluids, polymers and soft matter. Written by authors who are actively participating in the current development, this collection of 150 articles has the breadth and depth to be a major contributor toward defining the field of computational materials. In addition, there are 40 commentaries by highly respected researchers, presenting various views that should interest the future generations of the community. Subject Editors: Martin Bazant, MIT; Bruce Boghosian, Tufts University; Richard Catlow, Royal Institution; Long-Qing Chen, Pennsylvania State University; William Curtin, Brown University; Tomas Diaz de la Rubia, Lawrence Livermore National Laboratory; Nicolas Hadjiconstantinou, MIT; Mark F. Horstemeyer, Mississippi State University; Efthimios Kaxiras, Harvard University; L. Mahadevan, Harvard University; Dimitrios Maroudas, University of Massachusetts; Nicola Marzari, MIT; Horia Metiu, University of California Santa Barbara; Gregory C. Rutledge, MIT; David J. Srolovitz, Princeton University; Bernhardt L. Trout, MIT; Dieter Wolf, Argonne National Laboratory.
Author: Sanjay K. Sondhi
Publisher:
ISBN:
Category : Beryllium compounds
Languages : en
Pages : 286
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Author:
Publisher: Elsevier
ISBN: 0081028660
Category : Science
Languages : en
Pages : 4871
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Book Description
Materials in a nuclear environment are exposed to extreme conditions of radiation, temperature and/or corrosion, and in many cases the combination of these makes the material behavior very different from conventional materials. This is evident for the four major technological challenges the nuclear technology domain is facing currently: (i) long-term operation of existing Generation II nuclear power plants, (ii) the design of the next generation reactors (Generation IV), (iii) the construction of the ITER fusion reactor in Cadarache (France), (iv) and the intermediate and final disposal of nuclear waste. In order to address these challenges, engineers and designers need to know the properties of a wide variety of materials under these conditions and to understand the underlying processes affecting changes in their behavior, in order to assess their performance and to determine the limits of operation. Comprehensive Nuclear Materials, Second Edition, Seven Volume Set provides broad ranging, validated summaries of all the major topics in the field of nuclear material research for fission as well as fusion reactor systems. Attention is given to the fundamental scientific aspects of nuclear materials: fuel and structural materials for fission reactors, waste materials, and materials for fusion reactors. The articles are written at a level that allows undergraduate students to understand the material, while providing active researchers with a ready reference resource of information. Most of the chapters from the first Edition have been revised and updated and a significant number of new topics are covered in completely new material. During the ten years between the two editions, the challenge for applications of nuclear materials has been significantly impacted by world events, public awareness, and technological innovation. Materials play a key role as enablers of new technologies, and we trust that this new edition of Comprehensive Nuclear Materials has captured the key recent developments. Critically reviews the major classes and functions of materials, supporting the selection, assessment, validation and engineering of materials in extreme nuclear environments Comprehensive resource for up-to-date and authoritative information which is not always available elsewhere, even in journals Provides an in-depth treatment of materials modeling and simulation, with a specific focus on nuclear issues Serves as an excellent entry point for students and researchers new to the field
Author: Anuj Kumar
Publisher: CRC Press
ISBN: 1040043534
Category : Technology & Engineering
Languages : en
Pages : 327
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Book Description
High Entropy Materials covers the fundamental concepts of these materials and their emerging applications. To fulfil growing energy demand, scientists are looking for novel materials which can be used for the fabrication of high-performance energy devices. Many materials such as graphene, carbon nanotubes, and metal oxides are used in energy production and storage. A new class of metal oxides, multicomponent metal oxides, known as high entropy materials, have attracted considerable attention not only for their energy applications but also other emerging applications such as use in sensors, catalysts, and CO2 absorption. Key Features: Reviews state-of-the-art developments Provides new directions to scientists, researchers, and students to better understand the principles, technologies, and applications of high entropy materials Discusses ongoing challenges and visions for the future
