Download or read book Evolution of Radiation Induced Defects in SiC written by Hao Jiang and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Because of various excellent properties, SiC has been proposed for many applications in nuclear reactors including cladding layers in fuel rod, fission products container in TRISO fuel, and first wall/blanket in magnetic controlled fusion reactors. Upon exposure to high energy radiation environments, point defects and defect clusters are generated in materials in amounts significantly exceeding their equilibrium concentrations. The accumulation of defects can lead to undesired consequences such as crystalline-to-amorphous transformation1, swelling, and embrittlement, and these phenomena can adversely affect the lifetime of SiC based components in nuclear reactors. It is of great importance to understand the accumulation process of these defects in order to estimate change in properties of this material and to design components with superior ability to withstand radiation damages. Defect clusters are widely in SiC irradiated at the operation temperatures of various reactors. These clusters are believed to cause more than half of the overall swelling of irradiated SiC and can potentially lead to lowered thermal conductivity and mechanical strength. It is critical to understand the formation and growth of these clusters. Diffusion of these clusters is one importance piece to determine the growth rate of clusters; however it is unclear so far due to the challenges in simulating rare events. Using a combination of kinetic Activation Relaxation Technique with empirical potential and ab initio based climbing image nudged elastic band method, I performed an extensive search of the migration paths of the most stable carbon tri-interstitial cluster in SiC. This research reveals paths with the lowest energy barriers to migration, rotation, and dissociation of the most stable cluster. Based on these energy barriers, I concluded defect clusters are thermally immobile at temperatures lower than 1500 K and can dissociate into smaller clusters and single interstitials at temperatures beyond that. Even though clusters cannot diffuse by thermal vibrations, we found they can migrate at room temperature under the influence of electron radiation. This is the first direct observation of radiation-induced diffusion of defect clusters in bulk materials. We show that the underlying mechanism of this athermal diffusion is elastic collision between incoming electrons and cluster atoms. Our findings suggest that defect clusters may be mobile under certain irradiation conditions, changing current understanding of cluster annealing process in irradiated SiC. With the knowledge of cluster diffusion in SiC demonstrated in this thesis, we now become able to predict cluster evolution in SiC with good agreement with experimental measurements. This ability can enable us to estimate changes in many properties of irradiated SiC relevant for its applications in reactors. Internal interfaces such as grain boundaries can behave as sinks to radiation induced defects. The ability of GBs to absorb, transport, and annihilate radiation-induced defects (sink strength) is important to understand radiation response of polycrystalline materials and to better design interfaces for improved resistance to radiation damage. Nowadays, it is established GBs' sink strength is not a static property but rather evolves with many factors, including radiation environments, grain size, and GB microstructure. In this thesis, I investigated the response of small-angle tilt and twist GBs to point defects fluxes in SiC. First of all, I found the pipe diffusion of interstitials in tilt GBs is slower than bulk diffusion. This is because the increased interatomic distance at dislocation cores raises the migration barrier of interstitial dumbbells. Furthermore, I show that both the annihilation of interstitials at jogs and jog nucleation from clusters are diffusion-controlled and can occur under off-stoichiometric interstitial fluxes. Finally, a dislocation line model is developed to predict the role of tilt GBs in annihilating radiation damage. The model predicts the role of tilt GBs in annihilating defects depends on the rate of defects segregation to and diffusion along tilt GBs. Tilt GBs mainly serve as diffusion channel for defects to reach other sinks when defect diffusivity is high at boundaries. When defect diffusivity is low, most of the defects segregated to tilt GBs are annihilated by dislocation climb. Up-to-date, the response of twist GBs under irradiation has been rarely reported in literature and is still unclear. It is important to develop atom scale insight on this question in order to predict twist GBs' sink strength for a better understanding of radiation response of polycrystalline materials. By using a combination of molecular dynamics and grand canonical Monte Carlo, here I demonstrate the defect kinetics in {001} and {111} twist GBs and the microstructural evolution of these GBs under defect fluxes in SiC. I found due to the deep potential well for interstitials at dislocation intersections within the interface, the mobility of defects on dislocation grid is retard and this leads to defect accumulation at GBs for many cases. Furthermore, I conclude both types of twist GBs have to form mixed dislocations with edge component in order to absorb accumulated interstitials at the interface. The formation of mixed dislocation is either by interstitial loop nucleation or by dislocation reactions at the interface. The continuous formation and climb of these mixed dislocations make twist GBs unsaturatable sinks to radiation induced defects.

Download or read book Defect Structure and Evolution in Silicon Carbide Irradiated to 1 Dpa SiC at 1100 C written by and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Transmission electron microscopy (TEM), swelling measurements, isochronal annealing, and thermal diffusivity testing were used to characterize the effects of radiation damage in SiC. Together, these techniques provided a comprehensive set of tools for observing and characterizing the structure and evolution of radiation-induced defects in SiC as a function of irradiation temperature and dose. In this study, two types of dense, crystalline, monolithic SiC were subjected to irradiation doses up to 1 dpa-SiC at a temperature of 1100 C, as well as post-irradiation annealing up to 1500 C. The microscopic defect structures observed by TEM were correlated to changes in the macroscopic dimensions, thermal diffusivity and thermal conductivity. The results demonstrated the value of using ultrapure [beta]SiC as an effective reference material to characterize the nature of expected radiation damage in other, more complex, SiC-based materials such as SiC/SiC composites.

Download or read book Computational Modeling of Radiation Phenomenon in SiC for Nuclear Applications written by Hyunseok Ko and published by . This book was released on 2017 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: Silicon carbide (SiC) material has been investigated for promising nuclear materials owing to its superior thermo-mechanical properties, and low neutron cross-section. While the interest in SiC has been increasing, the lack of fundamental understanding in many radiation phenomena is an important issue. More specifically, these phenomena in SiC include the fission gas transport, radiation induced defects and its evolution, radiation effects on the mechanical stability, matrix brittleness of SiC composites, and low thermal conductivities of SiC composites. To better design SiC and SiC composite materials for various nuclear applications, understanding each phenomenon and its significance under specific reactor conditions is important. In this thesis, we used various modeling approaches to understand the fundamental radiation phenomena in SiC for nuclear applications in three aspects: (a) fission product diffusion through SiC, (b) optimization of thermodynamic stable self-interstitial atom clusters, (c) interface effect in SiC composite and their change upon radiation. In (a) fission product transport work, we proposed that Ag/Cs diffusion in high energy grain boundaries may be the upper boundary in unirradiated SiC at relevant temperature, and radiation enhanced diffusion is responsible for fast diffusion measured in post-irradiated fuel particles. For (b) the self-interstitial cluster work, thermodynamically stable clusters are identified as a function of cluster size, shape, and compositions using a genetic algorithm. We found that there are compositional and configurational transitions for stable clusters as the cluster size increases. For (c) the interface effect in SiC composite, we investigated recently proposed interface, which is CNT reinforced SiC composite. The analytical model suggests that CNT/SiC composites have attractive mechanical and thermal properties, and these fortify the argument that SiC composites are good candidate materials for the cladding. We used grand canonical monte carlo to optimize the interface, as a part of the stepping stone for further study using the interface.

Download or read book Radiation Effects in Silicon Carbide written by A.A. Lebedev and published by Materials Research Forum LLC. This book was released on 2017 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book reviews the most interesting research concerning the radiation defects formed in 6H-, 4H-, and 3C-SiC under irradiation with electrons, neutrons, and some kinds of ions. The electrical parameters that make SiC a promising material for applications in modern electronics are discussed in detail. Specific features of the crystal structure of SiC are considered. It is shown that, when wide-bandgap semiconductors are studied, it is necessary to take into account the temperature dependence of the carrier removal rate, which is a standard parameter for determining the radiation hardness of semiconductors. The carrier removal rate values obtained by irradiation of various SiC polytypes with n- and p-type conductivity are analyzed in relation to the type and energy of the irradiating particles. The influence exerted by the energy of charged particles on how radiation defects are formed and conductivity is compensated in semiconductors under irradiation is analyzed. Furthermore, the possibility to produce controlled transformation of silicon carbide polytype is considered. The involvement of radiation defects in radiative and nonradiative recombination processes in SiC is analyzed. Data are also presented regarding the degradation of particular SiC electronic devices under the influence of radiation and a conclusion is made regarding the radiation resistance of SiC. Lastly, the radiation hardness of devices based on silicon and silicon carbide are compared.

Download or read book A Low Temperature Photoluminescence Study of Radiation Induced Defects in Silicon Carbide written by and published by . This book was released on 2006 with total page 402 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electrical Characterization of Radiation Induced Defects in 3C SiC written by Matthew John Cabral and published by . This book was released on 2013 with total page 96 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Multiscale Modeling of Evolution of SiC Microstructure Due to Radiation and Corrosion written by Cheng Liu and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: SiC is an attractive material for nuclear energy, aerospace and semiconductor industries because of its uniquely combined properties, such as high-temperature strength, low neutron cross section, excellent corrosion and oxidation resistance, wide band-gap and low thermal expansion coefficient. Current and proposed applications include nuclear fuel components, nuclear structural components, airplane turbines, aerospace thermal protection layers and semiconductor electronics, etc. High temperature, irradiation and oxidizing environments can lead to degradation of SiC and its reduced reliability in application systems. This thesis is focused on understanding radiation-induced defects generation and evolution and as well as mechanisms of environmental degradation. Firstly, I report a statistical analysis of sizes and compositions of clusters produced in cascades during irradiation of SiC. The results are obtained by integrating molecular dynamics simulations of cascades caused by primary knock-on atoms (PKAs) over PKA energy spectrum derived from Stopping Range of Ions in Matter (SRIM) code. It is found that distributions of cluster size n obey a power law [f=A/n^S] and these clusters are dominated by carbons defects. Secondly, distribution of black spot defects (BSDs) and small clusters in irradiated 3C-SiC has been investigated by combining microscopy characterization with cluster dynamics (CD) model. It is found that there are small clusters identified in scanning transmission electron microscopy (STEM) invisible in TEM images. Simulations showed that both established properties of point defects (PDs) generation, reaction, clustering, and cluster dissociation, and additional phenomena of clusters generation, diffusion and morphology preference are necessary to be considered in a predictive model on cluster evolution in ion irradiated SiC. Then, based on CD model above, I developed a swelling model to estimate the swelling contributed by defects, which qualitatively explains that the swelling estimated based on X-Ray diffraction (XRD) is larger than that based on TEM is because there are PDs and small clusters invisible from TEM. Lastly, our molecular dynamics simulations show Incoherent grain boundaries (GBs) were more vulnerable to oxidation than single crystals, whereas oxidation of bicrystals with coherent GBs proceeded at a similar rate to that on single crystals. The accelerated oxidation along incoherent GBs can be attributed to larger free volume and silicon atoms with more negative charge state near GBs.

Download or read book Fundamentals of Radiation Materials Science written by GARY S. WAS and published by Springer. This book was released on 2016-07-08 with total page 1014 pages. Available in PDF, EPUB and Kindle. Book excerpt: The revised second edition of this established text offers readers a significantly expanded introduction to the effects of radiation on metals and alloys. It describes the various processes that occur when energetic particles strike a solid, inducing changes to the physical and mechanical properties of the material. Specifically it covers particle interaction with the metals and alloys used in nuclear reactor cores and hence subject to intense radiation fields. It describes the basics of particle-atom interaction for a range of particle types, the amount and spatial extent of the resulting radiation damage, the physical effects of irradiation and the changes in mechanical behavior of irradiated metals and alloys. Updated throughout, some major enhancements for the new edition include improved treatment of low- and intermediate-energy elastic collisions and stopping power, expanded sections on molecular dynamics and kinetic Monte Carlo methodologies describing collision cascade evolution, new treatment of the multi-frequency model of diffusion, numerous examples of RIS in austenitic and ferritic-martensitic alloys, expanded treatment of in-cascade defect clustering, cluster evolution, and cluster mobility, new discussion of void behavior near grain boundaries, a new section on ion beam assisted deposition, and reorganization of hardening, creep and fracture of irradiated materials (Chaps 12-14) to provide a smoother and more integrated transition between the topics. The book also contains two new chapters. Chapter 15 focuses on the fundamentals of corrosion and stress corrosion cracking, covering forms of corrosion, corrosion thermodynamics, corrosion kinetics, polarization theory, passivity, crevice corrosion, and stress corrosion cracking. Chapter 16 extends this treatment and considers the effects of irradiation on corrosion and environmentally assisted corrosion, including the effects of irradiation on water chemistry and the mechanisms of irradiation-induced stress corrosion cracking. The book maintains the previous style, concepts are developed systematically and quantitatively, supported by worked examples, references for further reading and end-of-chapter problem sets. Aimed primarily at students of materials sciences and nuclear engineering, the book will also provide a valuable resource for academic and industrial research professionals. Reviews of the first edition: "...nomenclature, problems and separate bibliography at the end of each chapter allow to the reader to reach a straightforward understanding of the subject, part by part. ... this book is very pleasant to read, well documented and can be seen as a very good introduction to the effects of irradiation on matter, or as a good references compilation for experimented readers." - Pauly Nicolas, Physicalia Magazine, Vol. 30 (1), 2008 “The text provides enough fundamental material to explain the science and theory behind radiation effects in solids, but is also written at a high enough level to be useful for professional scientists. Its organization suits a graduate level materials or nuclear science course... the text was written by a noted expert and active researcher in the field of radiation effects in metals, the selection and organization of the material is excellent... may well become a necessary reference for graduate students and researchers in radiation materials science.” - L.M. Dougherty, 07/11/2008, JOM, the Member Journal of The Minerals, Metals and Materials Society.

Download or read book Spectroscopic Studies of Irradiation Induced Defects in SiC written by Fredrik Carlsson and published by . This book was released on 2003 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electrical Characterization of Process and Radiation induced Defects in 4H SiC written by Ezekiel Omotoso and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Devices for operation in aerospace, manufacturing industries, defence and radiation-harsh environments need to be manufactured from materials that are resistant to the frequent damage caused by irradiation and high-temperature environments. Silicon carbide (SiC) is a wide-bandgap semiconductor material that promises to provide solutions to these problems based on its capability to operate under extreme conditions of temperature and radiation. These conditions introduce defects in the materials. Such defects play an important role in determining the properties of devices, albeit beneficial or detrimental. Therefore it is very important to characterize the defects present in as-grown material as well as defects introduced during processing and irradiation. In this research, resistive evaporation (RE) as well as electron-beam deposition was employed for the fabrication of ohmic and Schottky barrier contacts on nitrogen-doped, n-type 4H-SiC substrate. The quality of the Schottky barrier diodes (SBDs) deposited was confirmed by current-voltage (I-V) and capacitance-voltage (C-V) measurements. Deep level transient spectroscopy (DLTS) and high-resolution Laplace DLTS were successfully used to characterize the electrically active defects present in the 4H-SiC SBDs before and after bombarding them with high-energy electrons and alpha-particles as well as after exposing the sample to electron beam deposition conditions. I-V and C-V measurements showed that the SBDs deposited by RE were of good quality with an ideality factor close to unity, a low series resistance and low reverse leakage current. After irradiation, the electrical properties deviated significantly based on the irradiation types and fluences. Thermionic emission dominated at high temperatures close to room temperature, while other current transport mechanisms became dominant at lower temperatures. The ideality factor increased and Schottky barrier heights decreased with decreasing temperature.

Download or read book Role of Defects in Swelling and Creep of Irradiated SiC written by and published by . This book was released on 2016 with total page 35 pages. Available in PDF, EPUB and Kindle. Book excerpt: Silicon carbide is a promising cladding material because of its high strength and relatively good corrosion resistance. However, SiC is brittle and therefore SiC-based components need to be carefully designed to avoid cracking and failure by fracture. In design of SiC-based composites for nuclear reactor applications it is essential to take into account how mechanical properties are affected by radiation and temperature, or in other words, what strains and stresses develop in this material due to environmental conditions. While thermal strains in SiC can be predicted using classical theories, radiation-induced strains are much less understood. In particular, it is critical to correctly account for radiation swelling and radiation creep, which contribute significantly to dimensional instability of SiC under radiation. Swelling typically increases logarithmically with radiation dose and saturates at relatively low doses (damage levels of a few dpa). Consequently, swelling-induced stresses are likely to develop within a few months of operation of a reactor. Radiation-induced volume swelling in SiC can be as high as 2%, which is significantly higher than the cracking strain of 0.1% in SiC. Swelling-induced strains will lead to enormous stresses and fracture, unless these stresses can be relaxed via some other mechanism. An effective way to achieve stress relaxation is via radiation creep. Although it has been hypothesized that both radiation swelling and radiation creep are driven by formation of defect clusters, existing models for swelling and creep in SiC are limited by the lack of understanding of specific defects that form due to radiation in the range of temperatures relevant to fuel cladding in light water reactors (LWRs) (

Download or read book MAX Phases written by Michel W. Barsoum and published by John Wiley & Sons. This book was released on 2013-11-13 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this comprehensive yet compact monograph, Michel W. Barsoum, one of the pioneers in the field and the leading figure in MAX phase research, summarizes and explains, from both an experimental and a theoretical viewpoint, all the features that are necessary to understand and apply these new materials. The book covers elastic, electrical, thermal, chemical and mechanical properties in different temperature regimes. By bringing together, in a unifi ed, self-contained manner, all the information on MAX phases hitherto only found scattered in the journal literature, this one-stop resource offers researchers and developers alike an insight into these fascinating materials.

Download or read book Deep Level Transient Spectroscopy Studies of Radiation Induced Defects in Silicon written by John Richard Troxell and published by . This book was released on 1979 with total page 317 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Computational Characterization of Radiation induced Defect Dynamics and Material Response written by Miaomiao Jin and published by . This book was released on 2019 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt: Material degradation due to radiation damage poses serious concern on the reliability and durability of any reactor design. To understand material performance under the extreme environments combining high temperature and intense irradiation, the response of radiation damage must be meticulously analyzed, both experimentally and computationally. These efforts will not only bridge the knowledge gap in the fundamental understanding of physical processes, but also allow for prediction of material behavior under a variety of conditions and development of novel materials with superior radiation tolerance. This thesis investigates multiple aspects of radiation damage in materials using various computational methods over a wide range of time and length scale, including atomistic description of defect dynamics, multiscale simulations of radiation processes, and artificial intelligence prediction of material responses based on experimental studies. Firstly, to resolve the fundamental mechanisms of radiation-induced behavior, the traditional molecular dynamics simulations on single-atom damage cascade is extended by developing an algorithm to appropriately introduce numerous consecutive cascades; hence, an experimental dose level on the order of dpa (displacement per atom) can be achieved to enable realistic understanding of observed material responses. It has been utilized to examine the radiation behaviors in solid-solution alloys and nanocrystalline metals such as defect dynamics and grain boundary migration. Secondly, to break the intrinsic limitation of scale in atomistic simulations, a multiscale microstructural evolution framework that links binary-collision approximation, molecular dynamics and cluster dynamics is built to describe mesoscale experimental observations. It is used to successfully explain the non-power-law defect distribution in irradiated tungsten. This tool can be generalized to study the spatial dependent defect evolution in materials under ion irradiation. Finally, to bypass the physics-based complexity of describing materials evolution in real applications, a holistic view enabled by machine learning techniques is utilized, and applied to predict the onset of void swelling in metals with a manually collection of data from experimental studies. The model has generated satisfying results for prediction of unseen data based on material properties and experimental parameters.

Download or read book Atomic Resolution Investigation of Irradiation Induced Defects in Silicon Carbide written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Ionization induced Annealing of Pre existing Defects in Silicon Carbide written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A long-standing objective in materials research is to find innovative ways to remove preexisting damage and heal fabrication defects or environmentally induced defects in materials. Silicon carbide (SiC) is a fascinating wide-band gap semiconductor for high-temperature, high-power, high-frequency applications. Its high corrosion and radiation resistance makes it a key refractory/structural material with great potential for extremely harsh radiation environments. Here we show that the energy transferred to the electron system of SiC by energetic ions via inelastic ionization processes results in a highly localized thermal spike that can effectively heal preexisting defects and restore the structural order. This work reveals an innovative self-healing process using highly ionizing ions, and it describes a critical aspect to be considered in modeling SiC performance as either a functional or a structural material for device applications or high-radiation environments.

Download or read book Formation and Growth of Irradiation induced Defect Structures in Ceria written by Bei Ye and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Radiation damage effects are of primary concern for materials used in nuclear energy production. In this study, emphasis was given to the processes of formation and growth of radiation-induced defect structures in oxide fuels. Due to the natural complexity of oxide fuels, which consist of both a metal sublattice and an oxygen sublattice, radiation effects are much more complex in oxides than in metals. As a result, there are many radiation effects that are still not well understood despite numerous research efforts engaged in the past. This study was aimed to help clarify some of these effects, such as the evolution process of dislocation structures during irradiation and how it is affected by various irradiation conditions. In order to develop an understanding of the radiation damage process in the common fluorite-type ceramic oxide fuel, ceria (CeO2) was selected as a surrogate material of UO2 for this study. According to previous studies, ceramic materials with a fluorite crystal structure possess high radiation tolerance. Using CeO2 single crystals allowed for the observation of the intrinsic behavior of defects while excludes the effects of grain boundaries. To reveal the basic mechanisms responsible for the evolution of microstructure induced by irradiations, a group of coordinated experiments were designed by incorporating multiple techniques consisting of ion irradiation, in situ transmission electron microscopy (TEM) and ex situ TEM observation. Radiation damage in the materials was induced by irradiating them with krypton and xenon ions from an accelerator. Irradiation experiments were conducted at three temperature regimes: room temperature, 600°C and 800°C, in order to inspect the temperature dependence of atomic defect transportation. Ion energies were carefully chosen for low and high energy irradiations in order to produce a deposited ion peak within the specimen at low energy and a uniform distribution of defects at high energy. In situ TEM analysis was used in order to take advantage of real-time recording of defect nucleation and growth under gas ion irradiation, and ex situ TEM analysis was used to characterize the radiation-induced features at high image resolution along with complementary elemental analysis techniques such as X-ray energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS). In addition to the experimental investigation, a rate theory model, as a part of the multi-scale simulation approach, was employed to study the growth behaviors of dislocation loops. The computational results were found to be consistent with the experimental observations.