Download or read book The Systematic Study of Deformation and Fracture Mechanism of Nano Crystalline Nickel written by Manish Sharma and published by . This book was released on 2020-04-14 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt: The present study is initiated with the specific objective of observing, both during and after deformation in Nickel Crystal by TEM experiments, the mechanisms of the deformation and fracture using state of the art experimental tools in high purity, fully dense nanocrystalline metals with a narrow range of gain sizes. The goal is to develop a strategy to reach the rational design of nanomaterials i.e. nanocrystal Nickel with modelled and controlled particles size, morphology, orientation, and crystal structure, i.e. purpose-built nanomaterials, to probe, tune, and optimize their physical, chemical properties and mechanical properties. In our view, to achieve such ambitious challenge, the most pertinent parameter to monitor is the dislocation mechanism of the system. In an attempt to take part in the fascinating nanoworld, and to contribute to its ambitious challenges, the present review will expose the outcome of a novel general concept of nucleation, growth, thin film processing method. Now a days, new concepts of nanocomposites and nano glasses are also being investigated with special emphasis on ceramic composites to increase their strength and toughness. There appears to be a great potential for applications in the near future for nanocrystalline materials. The extensive investigations in recent years on structure-property correlations in nanocrystalline materials have begun to unravel the complexities of these materials, and pave the way for successful exploitation of alloy design principles to synthesize better materials than hitherto available. For the first time, direct and compelling conclusive evidence of the deformation mechanism crossover is provided. In addition, unexpected dislocation activities are also observed in grains as small as 5 nm. Nano beam diffraction observations revealed that a nanocrystalline grain with a size of about 20 nm may experience ultrahigh elastic strain during deformation and the implication of this finding is discussed in detail. Also Understanding the formation mechanisms and role of grain agglomerates in nanocrystalline metals is expected to directly impact the processing methods required to create nanocrystalline metals with improved strength and ductility.
Download or read book Study of Deformation Behavior of Nanocrystalline Nickel Using Nanoindentation Techniques written by Changli Wang and published by . This book was released on 2010 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanocrystalline materials with grain size less than 100 nm have been receiving much attention because of their unparallel properties compared with their microcrystalline counterparts. Because of its high hardness, nanocrystalline nickel has been used for MEMS. Long term thermomechnical properties and deformation mechanism at both ambient and elevated temperatures need to be evaluated which is vital for reliability of its applications as structural material. In this thesis, nanoindentation creep of nanocrystalline nickel with an as-deposited grain size of 14 nm was characterized at elevated temperatures. The nanoindentation creep rate was observed to scale with temperature and applied load (or stress), and could be expressed by an empirical power-law equation for describing conventional crystalline solids. Creep activation energy was found to be close to that for grain boundary self-diffusion in nickel. The activation volume was also evaluated using a stress relaxation technique. The creep results were compared with those for fine-grained nickel in the literature. Possible mechanisms were discussed in light of the creep rate and temperature ranges. To provide a direct comparison, uniaxial creep tests were conducted on nanocrystalline nickel with an as-deposited grain size of 14 nm at 398 K. It was found that stress exponents under the two test conditions are almost the same, indicating a similar creep mechanism. However, the strain rate measured by nanoindentation creep was about 100 times faster than that by uniaxial creep. The rate difference was discussed in terms of stress states and the appropriate selection of Tabor factor. To further explore the time-dependent plastic behavior, multiple unload-reload tests were conducted on electrodeposited nanocrystalline nickel in both compression and tension. A hysteresis was observed during each unload-reload cycle, indicating irreversible energy dissipation. The dissipated energy was evaluated and the energy dissipation rate was found to increase with the flow stress to the third power and sensitive to the stress state (tension or compression). A mechanistic model based on grain boundary sliding was proposed to describe the unload-reload behavior. Experimental results were found to be in good agreement with the model predictions, suggesting the observed hysteresis was indeed caused by grain boundary sliding.
Download or read book Deformation Mechanisms of Nanocrystalline Nickel Studied by In situ X ray Diffraction written by Stefan Brandstetter and published by . This book was released on 2009 with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Partij van de Arbeid Een stukje geschiedenis written by and published by . This book was released on 1971 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Plastic Deformation in Nanocrystalline Materials written by Mikhail Gutkin and published by Springer Science & Business Media. This book was released on 2013-04-18 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: It seems there is no special need to comment on the term 'nanostructure' now, when one often meets the 'nano' words not only in scientific journals but even in newspapers. Moreover, today they are even to be heard in TV and radio programmes. In academic science, where the terms 'nanostructure' and 'nan otechnology' have been extremely popular since the early 1990s, they have been successfully extended to the sphere of economics and business, and now to politics. This is quite natural because nanostructures and nanotechnolo gies will surely serve as a basis for the most advanced and highest technology production in the nearest and probably also the remote future. Hence, the struggle to create and occupy its markets is already under way. In this respect, it is of great interest to review data on the dynamics of U. S. Federal Goverment expenditure for nanotechnology [1,2]. In the fiscal years 1997 and 2002, expenditure was approximately US$116 and US$ 697 million, respectively. In the fiscal year 2004, the President's request for US federal in vestment in nanoscale science, engineering and technology is about US$ 849 million [2]. The indicative budget allocated to the Thematic Priority enti tled 'Nanotechnologies and nanosciences, knowledge-based multifunctional materials and new production processes and devices' for the duration 2002- 2006 of the sixth EU Framework Programme for Research and Technological Development is EUR 1300 million [3].
Download or read book Cold Rolling Texture of Electrodeposited Nanocrystalline FCC Metals written by Yanling Yang and published by American Academic Press. This book was released on 2018-01-16 with total page 131 pages. Available in PDF, EPUB and Kindle. Book excerpt: Properties of nanocrystalline metals or alloys cannot be predicted according to the phenomena observed in traditional coarse-grained materials. Nanocrystalline materials exhibit special physical and chemical properties, such as extremely high mechanical strength, outstanding thermal, optical, magnetic and electrical properties. Deformation mechanisms of nanocrystalline materials have been discussed for many years. Previous literatures mainly focus on the investigation of deformation behaviors through in-situ experimental methods such as in-situ TEM observation or simulation methods by modeling. With regard to the in-situ TEM observation, it still remains controversial whether the TEM results can represent the deformation behaviors of bulk nanocrystalline materials. In line with the molecular dynamics simulation method, the materials are frequently assumed to be ideal and the strain rate utilized is extraordinarily high. All the above conditions almost cannot be met or validated through experiments. In this work, it is attempted to explore deformation mechanisms of nanocrystalline face-centered cubic metals or alloys based on texture evolution during plastic deformation. Dislocation movements in plastic deformation process are always followed by formation of deformation texture in most cases, and plastic deformation coordinated by grain boundary sliding and/or grain rotation mechanisms does not incur the occurrence of crystallographic texture. Therefore, investigations on texture evolution during plastic deformation are able to provide powerful evidence for the deformation mechanisms of nanocrystalline materials.
Download or read book Deformation Study of Nanocrystalline Ni fe Alloy Using Synchroton Diffraction written by Li Li and published by . This book was released on 2010 with total page 115 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation addresses two critical issues in the deformation of nc metals and alloys: (1) A stress-induced genuine grain growth after the plastic deformation rather than just a change of the grain shape; (2) A systematically quantitative study of micrsostructural evolution during the plastic deformation. These two critical issues point to the deformation of nc materials with the average-grain sizes within the range of 10 to 50 nm, which is the most interesting and controversial region in the current time. The current study provides a systematic and detailed microstructural evolution for this region, which is definitely beneficial for the investigation of the deformation mechanism in this region, especially for the simulation. The main experimental and data-analysis methods employed in this research are synchrotron high-energy X-ray diffraction, X-ray line profile analysis, and texture analysis. The combination of these methods is beneficial to the accurate microstructural interpretation of the bulk materials.
Download or read book Synthesis and Deformation of Nanocrystalline Nickel written by Zunayed Ahmed and published by . This book was released on 2001 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Deformation of Nanocrystalline Materials at Ultrahigh Strain Rates Microstructure Perspective in Nanocrystalline Nickel written by R. Smith and published by . This book was released on 2006 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanocrystalline materials with grain sizes smaller than 100 nm have attracted extensive research in the past decade. Due to their high strength, these materials are good candidates for high pressure shock loading experiments. In this paper, we investigated the microstructural evolutions of nanocrystalline nickel with grain sizes of 10-50 nm, shock-loaded in a range of pressures (20-70 GPa). A laser-driven isentropic compression process was applied to achieve high shock-pressures in a timescale of nanoseconds and thus the high-strain-rate deformation of nanocrystalline nickel. Postmortem transmission electron microscopy (TEM) examinations reveal that the nanocrystalline structures survive the shock deformation and that dislocation activity is the prevalent deformation mechanism when the grain sizes are larger than 30 nm, without any twinning activity at twice the stress threshold for twin formation in micrometer-sized polycrystals. However, deformation twinning becomes an important deformation mode for 10-20 nm grain-sized samples.
Download or read book Atomistic and Continuum Modeling of Nanocrystalline Materials written by Laurent Capolungo and published by Springer. This book was released on 2010-12-08 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Atomistic and Continuum Modeling of Nanocrystalline Materials develops a complete and rigorous state-of-the-art analysis of the modeling of the mechanical behavior of nanocrystalline (NC) materials. Among other key topics, the material focuses on the novel techniques used to predict the behavior of nanocrystalline materials. Particular attention is given to recent theoretical and computational frameworks combining atomistic and continuum approaches. Also, the most relevant deformation mechanisms governing the response of nanocrystalline materials are addressed and discussed in correlation with available experimental data.
Download or read book Investigation of Deformation and Failure Mechanisms in Nanoindentation Mechanics written by Yuzhi Xia (Researcher in materials science and engineering) and published by . This book was released on 2014 with total page 105 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation further extends nanoindentation to study the initiation of plasticity in single crystals in nanoscale stressed volumes, to the instrumented tests for damage evaluation and monitoring, and to the fundamental issues in deformation and failure mechanisms in relationship to the defect evolutions. In the first project, model Fe-Cr, Fe-Ni and Fe-Cr-Ni alloys that are the basis of many structural steels were synthesized as single crystals and characterized. The compositions investigated were Fe-15Cr, Fe-30Cr, Fe-30Ni and Fe-15Cr-15Ni (atomic percent). Several key mechanical properties were determined which will be useful in further studies of irradiation/deformation-induced defects. Incipient plasticity and slip characteristics were investigated by nanoindentation on (001) and surfaces. Finally, the effects of heterogeneous pop-in mechanisms are discussed in the context of incipient plasticity in the four different alloys. Moreover, the pop-in event mode and pop-in excursion are investigated. In previous literature, there are two kinds of pop-in mode: a single large displacement burst and multiple successive pop-ins. The size and microstructure effect are discussed for the two modes showing that multiple successive pop-ins is more likely to be appeared in fcc crystal with a smaller indenter tip. Also an analytical model is established to predict size effect in pop-in excursion for one large pop-in mode. The effect of the dislocation nucleation mechanism is discussed for the pop-in excursion. In the last project, the pinch-torsion test is designed to evaluate Li-ion cell safety. The failure mechanism of pinch-torsion test is examined by numerical simulations and comparisons to experimental observations. Finite element models are developed to evaluate the deformation of the separators under both pure pinch and pinch-torsion loading conditions. It is discovered that the addition of the torsion component significantly increased the maximum principal strain, which is believed to induce the internal short circuit. It is further found that the separator failure is achieved in the early stage of torsion (within a few degree of rotation).
Download or read book Deformation and Fracture in Materials written by Anoop Kumar Mukhopadhyay and published by CRC Press. This book was released on 2024-08-27 with total page 373 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides information on the basics of deformation and fracture in materials and on current, state-of-the-art experimental and numerical/theoretical methods, including data-driven approaches in the deformation and fracture study of materials. The blend of experimental test methods and numerical techniques to study deformation and fracture in materials is discussed. In addition, the application of data-driven approaches in predicting material performance in different types of loading and loading environments is illustrated. Features: Includes clear insights on deformation and fracture in materials, with clear explanations of mechanics and defects relating to them Provides effective treatments of modern numerical simulation methods Explores applications of data-driven approaches such as artificial intelligence, machine learning, and computer vision Reviews simple and basic experimental techniques to understand the concepts of deformation and fracture in materials Details modeling and simulation strategies of mechanics of materials at different scales This book is aimed at researchers and graduate students in fracture mechanics, finite element methods, and materials science.
Download or read book Microstructures and Mechanical Properties of Nanocrystalline Materials written by and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Mechanical Properties of Nanocrystalline Materials written by James C. M. Li and published by CRC Press. This book was released on 2011-09-02 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book concentrates on both understanding and development of nanocrystalline materials. The original relation that connects grain size and strength, known as the Hall-Petch relation, is studied in the nanometer grain size region. The breakdown of such a relation is a challenge. Why and how to overcome it? Is the dislocation mechanism still operating when the grain size is very small, approaching the amorphous limit? How do we go from the microstructure information to the continuum description of the mechanical properties?
Download or read book Fatigue Stress Concentration and Notch Sensitivity in Nanocrystalline Metals written by and published by . This book was released on 2016 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent studies have shown the potential for nanocrystalline metals to possess excellent fatigue resistance compared to their coarse-grained counterparts. Although the mechanical properties of nanocrystalline metals are believed to be particularly susceptible to material defects, a systematic study of the effects of geometric discontinuities on their fatigue performance has not yet been performed. In the present work, nanocrystalline Ni-40 wt%Fe containing both intrinsic and extrinsic defects were tested in tension-tension fatigue. The defects were found to dramatically reduce the fatigue resistance, which was attributed to the relatively high notch sensitivity in the nanocrystalline material. Microstructural analysis within the crack-initiation zones underneath the defects revealed cyclically-induced abnormal grain growth (AGG) as a predominant deformation and crack initiation mechanism during high-cycle fatigue. Furthermore, the onset of AGG and the ensuing fracture is likely accelerated by the stress concentrations, resulting in the reduced fatigue resistance compared to the relatively defect-free counterparts.
Download or read book Computational Modelling of the Mechanical Behavior of Nanocrystalline Metals Based on the Deformation Mechanisms and Their Transitions written by Baozhi Zhu and published by . This book was released on 2006 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: There has been a growing research interest in understanding the mechanical behaviors and the deformation mechanisms of nanocrystalline metals and alloys in the past a few decades, due to their extraordinary mechanical prosperities, such as high strength, hardness, and wear resistance, which have great potentials in engineering applications. As grain sizes in crystalline metals and alloys transit down to the lower end of the nanometer range, the plastic deformations are no longer dominated by the intragrain dislocation activities. Instead deformations assisted by grain boundary start to play a more important role in deciding the mechanical response of the bulk materials, as the interfacial volume fraction increases with the reduction of grain sizes. A polycrystalline constitutive theory is developed in the form of the extend aggregate Taylor model of Asaro and Needleman for the nanocrystalline metals. The plastic deformation description is based on the Asaro, Krysl and Kad (AKK) model, which considers deformation mechanisms such as the emission of perfect, partial dislocations and deformation twins from grain boundary and grain boundary sliding when the grain size is sufficiently small in the nanometer regime (less than 100nm), and their transitions are governed by the factors such as grain size, stacking fault energy, temperature, and strain rate, etc. Therefore the effect of grain size distributions in addition to the mean grain size is considered important on the mechanical response in this constitutive theory. The grain size distributions can be simulated with the experimentally determined lognormal distributions for the electro-deposited nanocrystalline metals for example. Numerical simulations are carried out for nanocrystalline Ni, Cu, Al and Pd, and the simulated phenomena include the mechanical response of these materials when subjected to uniaxial tension and compression under different deformation rates, texture development under high pressure torsion (HPT), and the grain growth effect during nanoindentation, etc, where the contribution of each deformation mechanism is carefully studied. The obtained numerical results are in reasonably good agreement with the experiments. Due to the fact that the deformation mechanisms in nanostructured materials are not yet fully understood, this constitutive theory will need to be further improved with the future findings of deformation mechanisms, which this theory has the flexibility to easily incorporate.
Download or read book Defects and Deformation in Nanostructured Metals written by Christopher Earl Carlton and published by . This book was released on 2009 with total page 394 pages. Available in PDF, EPUB and Kindle. Book excerpt: A better understanding of how the nanoscale environment affects the mechanical properties of materials, in particular metallic nanoparticles and nanocrystalline metals is vital to the development of next generation materials. Of special interest is obtaining a fundamental understanding of the inverse Hall-Petch Effect in nanocrystalline metals, and nanoindentation in individual nanoparticles. Understanding these subjects is critical to understanding how the mechanical properties of materials are fundamentally affected by nanoscale dimensions. These topics have been addressed by a combination of theoretical modeling and in-situ nanoindentation transmission electron microscopy (TEM) analysis. Specifically, the study of the inverse Hall-Petch effect in nanocrystalline metals will be investigated by a thorough review of the literature followed by a proposed novel theoretical model that better explains the experimentally observed behavior of nanocrystalline metals. On the other hand, the nanoindentation of individual nanoparticles is a very new research topic that has yet to aggregate a large body of experimental data. In this context, in-situ TEM nanoindentation experiments on silver nanoparticles will be first performed to determine the mechanisms of deformation in these nanostructures. A theoretical explanation for the observed deformation mechanisms will be then developed and its implications will be discussed. In addition to nanoparticles, this study will also provide unique and valuable insight into the deformation mechanisms of nanopillars, a growing area of research despite much controversy and speculation about their actual mechanisms of deformation. After studying the novel behavior of both nanocrystalline metals and nanoparticles, useful applications of both classes of materials will be explored. The discussion of applications will focus on utilizing the interesting behaviors explored in the dissertation. Of particular interest will be applications of nanoparticles and nanocrystalline materials to coatings, radiation resistance and super-plastic materials.
