Grain Boundary Effects on Microstructural Stability of Nanocrystalline Metallic Materials PDF Download

Author: Xiaofei Zhu
Publisher:
ISBN:
Category : Science
Languages : en
Pages :

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Book Description
Grain boundaries play an important role in dictating the mechanical and physical properties of nanocrystalline (NC) materials because of the increased volume fraction of intercrystalline components as the grain size decreases. In general, grain boundaries have a high energy level and there exists a thermodynamic driving force to reduce the overall area of grain boundaries through grain coarsening, making NC material systems intrinsically unstable. Recent investigations also indicate that mechanical deformation can promote grain growth in NC material even at the cryogenic temperatures. In this chapter, first, the current investigation on the grain boundary structures of NC metallic materials is briefly reviewed and then the state-of-the-art of experimental results on the microstructural stability during deformation processes is discussed. Finally, several key issues for improving the microstructure stability of NC metallic materials and possible future work are discussed.

Author: Tomasz Tański
Publisher: BoD – Books on Demand
ISBN: 9535128612
Category : Science
Languages : en
Pages : 186

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Book Description
This book contains eight chapters with original and innovative research studies in the field of grain boundaries. The results presented in the chapters of this book are very interesting and inspiring. This book will be very valuable to all researchers who are interested in the influence of grain boundaries on the structure and different kinds of properties of engineering materials. This book is also addressed to students and professional engineers working in the industry as well as to specialists who pay attention to all aspects related to grain boundaries and their impact on the various properties of innovative materials. The chapters of this book were developed by respected and well-known researchers from different countries.

Author: Satish Rajaram
Publisher:
ISBN:
Category : Grain boundaries
Languages : en
Pages : 230

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Book Description
Nanocrystalline (NC) materials, defined structurally by having average grain sizes less than 100nm, exhibit a number of enhanced mechanical properties such as ultrahigh strength, improved wear resistance and greater resistance to fatigue crack initiation compared to coarser grained polycrystalline (PC) materials. NC materials exhibit these improved properties, in part, due to the increased grain boundary (GB) volume fraction. NC materials strength increases with decreasing grain size, known as the Hall-Petch (HP) effect often resulting in a peak strength between 10-20nm. Studies have shown that NC materials strength decreases due to the shift from dislocation-dominant to GB-dominant deformation mechanisms in the plastic flow regime as average grain size decreases below 10-20nm. While the potential improved properties are of interest, the application of NC materials are hindered due to microstructural instability i.e., grain growth to reduce the total energy of the system, thus degrading desired mechanical properties. Numerous studies have looked at avenues to stabilize NC microstructure, namely through thermodynamics and kinetics, alloying has been one significant strategy used to stabilize NC materials. As these processes are used to stabilize NC microstructures to thermally-induce grain growth, they add additional uncertainty as the deformation and GB behavior of pure NC materials are still not fully understood. Experimental work on NC materials is difficult due to the length scale being investigated as it is difficult to manufacture and can be time consuming to analyze with current technology. Atomistic simulations have shown the potential to investigate fundamental behavior at the nanoscale and provide important insight in the mechanisms that drive the mechanical behavior of NC materials. This thesis will use atomistic simulations to study the structure-property relationship of face-centered-cubic (fcc) metals by focusing on GBs to investigate the strength of NC nickel. During the course of this thesis, four aspects that govern NC behavior will be studied, yielding, plasticity, thermal effects, and GB disorder to elucidate deeper insight into the underlying deformation mechanisms that control the strength of FCC NC metals i.e., flow stress, in the grain size regime 6 to 20nm.

Author: Jinyu Zhang
Publisher:
ISBN:
Category : Science
Languages : en
Pages :

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Book Description
The aim of this chapter is to shed light on the effects of grain boundary segregation on microstructural evolution in nanostructured metallic materials as well as on their mechanical properties. Several key topics will be covered. First, a brief explanation of mechanical stress-driven grain growth in nanostructured Al, Ni, and Cu thin films will be provided in terms of a deformation mechanism map. It will become clear that the excess energy of grain boundaries enable the nanostructured metals to suffer from significant microstructure evolution via dislocation-boundary interactions during plastic deformation even at room temperature. Manipulation of grain boundary structures/properties via dopants segregation at grain boundaries to inhibit grain coalescence associated with remarkably enhanced mechanical properties is then discussed in three representative binary Cu-based systems, id est, Cu-Zr, Cu-Al, and Cu-W. This is finally followed by a summary of this chapter.

Author: C. Barry Carter
Publisher: Springer
ISBN: 3319266519
Category : Technology & Engineering
Languages : en
Pages : 543

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Book Description
This text is a companion volume to Transmission Electron Microscopy: A Textbook for Materials Science by Williams and Carter. The aim is to extend the discussion of certain topics that are either rapidly changing at this time or that would benefit from more detailed discussion than space allowed in the primary text. World-renowned researchers have contributed chapters in their area of expertise, and the editors have carefully prepared these chapters to provide a uniform tone and treatment for this exciting material. The book features an unparalleled collection of color figures showcasing the quality and variety of chemical data that can be obtained from today’s instruments, as well as key pitfalls to avoid. As with the previous TEM text, each chapter contains two sets of questions, one for self assessment and a second more suitable for homework assignments. Throughout the book, the style follows that of Williams & Carter even when the subject matter becomes challenging—the aim is always to make the topic understandable by first-year graduate students and others who are working in the field of Materials Science Topics covered include sources, in-situ experiments, electron diffraction, Digital Micrograph, waves and holography, focal-series reconstruction and direct methods, STEM and tomography, energy-filtered TEM (EFTEM) imaging, and spectrum imaging. The range and depth of material makes this companion volume essential reading for the budding microscopist and a key reference for practicing researchers using these and related techniques.

Author: James C M Li
Publisher: World Scientific Publishing Company
ISBN: 9813105658
Category : Technology & Engineering
Languages : en
Pages : 454

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Book Description
This is the second volume of an advanced textbook on microstructure and properties of materials. (The first volume is on aluminum alloys, nickel-based superalloys, metal matrix composites, polymer matrix composites, ceramics matrix composites, inorganic glasses, superconducting materials and magnetic materials). It covers titanium alloys, titanium aluminides, iron aluminides, iron and steels, iron-based bulk amorphous alloys and nanocrystalline materials.There are many elementary materials science textbooks, but one can find very few advanced texts suitable for graduate school courses. The contributors to this volume are experts in the subject, and hence, together with the first volume, it is a good text for graduate microstructure courses. It is a rich source of design ideas and applications, and will provide a good understanding of how microstructure affects the properties of materials.Chapter 1, on titanium alloys, covers production, thermomechanical processing, microstructure, mechanical properties and applications. Chapter 2, on titanium aluminides, discusses phase stability, bulk and defect properties, deformation mechanisms of single phase materials and polysynthetically twinned crystals, and interfacial structures and energies between phases of different compositions. Chapter 3, on iron aluminides, reviews the physical and mechanical metallurgy of Fe3Al and FeAl, the two important structural intermetallics. Chapter 4, on iron and steels, presents methodology, microstructure at various levels, strength, ductility and strengthening, toughness and toughening, environmental cracking and design against fracture for many different kinds of steels. Chapter 5, on bulk amorphous alloys, covers the critical cooling rate and the effect of composition on glass formation and the accompanying mechanical and magnetic properties of the glasses. Chapter 6, on nanocrystalline materials, describes the preparation from vapor, liquid and solid states, microstructure including grain boundaries and their junctions, stability with respect to grain growth, particulate consolidation while maintaining the nanoscale microstructure, physical, chemical, mechanical, electric, magnetic and optical properties and applications in cutting tools, superplasticity, coatings, transformers, magnetic recordings, catalysis and hydrogen storage.

Author: Matthias Friedrich Funk
Publisher: KIT Scientific Publishing
ISBN: 3866449186
Category : Technology & Engineering
Languages : en
Pages : 218

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Book Description
Nanostructured metals with maximal grain or twin sizes of less than 100 nm have advanced properties like increased strength.As beneficial as these microstructures can be for the strength of materials, they are not infinitely stable. During mechanical loading these metals tend to coarsen and lose their beneficial structure. Besides electron microscopic analysis of fatigued samples, in situ cycling tests were conducted in order to observe structural degradation during mechanical loading.

Author: Mohammad Aramfard
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Book Description
Nanocrystalline (NC) metals with averaged grain size smaller than 100 nm have shown promising mechanical properties such as higher hardness and toughness than conventional coarse-grained metals. Unlike conventional metals in which the deformation is controlled by dislocation activities, the microstructural evolution in NC metals is mainly dominated by grain rotation and stress-driven grain boundary motion (SDGBM) due to the high density of grain boundaries (GBs). SDGBM is thus among the most studied modes of microstructural evolution in NC materials with particular interests on their fundamental atomistic mechanisms. In the first part of this thesis, molecular dynamics simulations were used to investigate the influences of Triple Junctions (TJs) on SDGBM of symmetric tilt GBs in copper by considering a honeycomb NC model. TJs exhibited asymmetric pinning effects to the GB migration and the constraints by the TJs and neighboring grains led to remarkable non-linear GB motion in directions both parallel and normal to the applied shear. Based on these findings, a generalized model for SDGBM in NC Cu was proposed. In the second part, the interaction of SDGBM with crack, voids and precipitates was investigated. It was found that depending on the GB structure, material type and temperature, there is a competition between different atomistic mechanisms such as crack healing, recrystallization and GB decohesion. It is hoped that the findings of this work could clarify the micro-mechanisms of various experimental phenomena such as grain refinement in metals during severe plastic deformation, which can be used to design optimized route of making stabilized bulk NC metals.

Author: Amirhossein Khalajhedayati
Publisher:
ISBN: 9781321996067
Category :
Languages : en
Pages : 127

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Book Description
Nanocrystalline metals have been the focus of current literature due to their interesting mechanical properties. This is a result of having nanometer sized grains and high volume fraction of grain boundaries. While these materials have high strength, the large number of boundaries is also responsible for the limited ductility and thermal instability often observed for nanocrystalline systems. Despite the current efforts in the literature, these challenges still prevent widespread use of nanocrystalline metals in real engineering applications. In this thesis, we study these problems by focusing on tailoring the grain boundary structure and chemistry and propose a methodology that can be used to mitigate those challenges. First, we study the plastic flow and failure as a function of grain boundary volume fraction (i.e., grain size) using microcompression in a nanocrystalline Ni-W. Since grain boundary physics are extremely important here, we also study how the relaxation of nonequilibrium grain boundaries affects failure. We show that nanocrystalline metals with larger grain boundary volume fractions and relaxed boundary structures are stronger, but also more likely to fail prematurely through catastrophic shear banding. We also show that shear banding can create a dynamic microstructure leading to grain coarsening. A major take-away from this work is that disordered grain boundaries can actually be beneficial. Therefore, in the next study we introduce amorphous complexions, highly disordered grain boundaries, through grain boundary doping as an all-in-one solution to design against failure and thermal instability. We use nanocrystalline Cu with the addition of Zr as our model system to explore complexion engineering in these materials. High resolution transmission electron microscopy in conjunction with energy dispersive x-ray spectroscopy demonstrates segregation of Zr to the boundaries of Cu-Zr alloys created with mechanical alloying. This provided evidence for the formation of amorphous grain boundaries complexions under certain conditions. Microcompression and in-situ bending experiments are then used to quantify the effect of doping on mechanical behavior. Finally, our results show that strength, strain-to-failure, failure mode, and thermal stability can be controlled with boundary doping. The proposed methodology described here is rather general and can be applied to other material systems to make bulk nanocrystalline metals with improved mechanical properties.

Author: P. E. J. Flewitt
Publisher: Wiley
ISBN: 9780471979517
Category : Technology & Engineering
Languages : en
Pages : 0

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Book Description
Over recent years the understanding of grain boundaries, interphase boundaries and free surfaces has advanced greatly, leading to a clear recognition that these discontinuities make a significant contribution to the physical and mechanical properties of materials from multiphase metals and alloys to electronic materials. Grain Boundaries -Their Microstructure and Chemistry discusses the interrelationship between microstructure and chemistry of the grain boundary, with particular emphasis on the influence of the environment (air, liquid and liquid metal) and composition (bulk and impurity). This highly practical volume presents a brief background to interphase and grain boundaries, before considering in detail grain boundary composition and composition changes, and how grain boundary composition affects material properties. Very recent advances in techniques such as electron energy loss spectroscopy, high-resolution transmission electron microscopy and atom probe, and the facinating new insights into grain boundary, microstructure that they have revealed, are also discussed. Grain Boundaries - Their Microstructure and Chemistry is an indispensable text for design and safety engineers in many industries, including power and aerospace, as well as for materials scientists and engineers in academia and research institutes.