Download or read book Characterization of Radiation Effects and Ab Initio Modeling of Defects in a High Entropy Alloy for Nuclear Power Application written by Congyi Li and published by . This book was released on 2018 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt: A novel Co-free NiFeMnCr HEA was synthesized for both ion and neutron irradiation studies. 3 and 5.8MeV heavy ion irradiations were conducted at room temperature and 400 - 700 °C from 0.03 to 10dpa. Post-irradiation examination included x-ray diffraction, nanoindentation hardness and transmission electron microscopy. The HEA exhibited quantitatively superior radiation resistance than conventional alloys, including suppressed void swelling and solute segregation. Neutron irradiation was conducted at 60 °C from 0.1 to 1dpa. Microhardness, electrical resistivity and positron annihilation spectroscopy measurements were performed at room temperature before and after isochronal annealing up to 700°C on the neutron-irradiated samples. The HEA retains fundamental stability after neutron irradiation. Compared with metals and conventional alloys, the HEA showed similar annealing trend of hardness and vacancy-type of defects. On the other hand, this HEA showed unique annealing trend of electrical resistivity. The large radiation induced resistivity increase (>10 [mu][Omega]·cm) did not recover up to 700 °C, suggesting short range ordering phenomena may be critical in radiation effects of HEA. In parallel, ab initio modeling was conducted to establish a solid foundation for multiscale modeling of HEA as well as to reveal unique defect physics of HEA. Magnetic structure was computed based on coherent potential. Vacancy energetics were computed by Vienna Ab initio Simulation Package (VASP). Modeling results shows that it is reasonable to neglect magnetic interactions. The statistical distribution of vacancy formation energy is weakly dependent upon either the chemical species of the atom site associated with the vacancy, or local chemical environment. The calculated migration energy values show a large spread, varying between 0.55 to 1.68eV, although the mean value is comparable to that of conventional austenitic alloys. Finally, positron lifetime of bulk HEA, mono-vacancy and small vacancy clusters were computed by a finite element based ab initio package to facilitate the interpretation of experimental results from positron annihilation spectroscopy.

Download or read book Radiation Behavior of High entropy Alloys for Advanced Reactors Final Report written by and published by . This book was released on 2015 with total page 121 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the first task, we have demonstrated the radiation damage and the recrystallization behaviors in multicomponent alloys through molecular-dynamics simulations. It is found that by alloying with atoms of different sizes, the atomic-level strain increases, and the propensity of the radiation-induced crystalline to amorphous transition increases as the defects cluster in the cascade body. Recrystallization of the radiation induced supercooled or glass regions show that by tuning the composition and the equilibrium temperature, the multicomponent alloys can be healed. The crystalline-amorphous-crystalline transitions predict the potential high radiation resistance in multicomponent alloys. In the second task, three types of high-entropy alloys (HEAs) were fabricated from AlCoCrFeNi and AlCuCrFeNi quinary alloys. Hardness and reduced contact modulus were measured using nanoindentation tests. Heavy ion irradiation were performed using 10 MeV gold and 5 MeV nickel to study radiation effects. Al0.5CrCuFeNi2 shows phase separation upon the presence of copper. Both hardness and contact modulus exhibit the same trend as increasing the applied load, and it indicates that excessive free volume may alter the growth rate of the plastic zone. The as-cast Al0.1CoCrFeNi specimen undergone the hot isostatic pressing (HIP) process and steady cooling rate which mitigate the quenching effect. The swelling behavior was characterized by the atomic force microscopy (AFM), and the swelling rate is approximately 0.02% dpa. Selected area diffraction (SAD) patters show irradiation-induced amorphization throughout the ion projected range. Within the peak damage region, an amorpous ring is observed, and a mixture of amorphous/ crystalline structure at deeper depth is found. The Al0.3CoCrFeNi HEAs shows good radiation resistance up to 60 peak dpa. No voids or dislocations are observed. The crystal structures remain face-centered-cubic (FCC) before and after 5 MeV Ni irradiation. Higher dpa might be required to study defects formation mechanisms. In the third task, all the constituent binary and ternary systems of the Al-Co-Cr-Fe-Ni system were thermodynamically modeled within the whole composition range. Comparisons between the calculated phase diagrams and literature data are in good agreement. The multi-component thermodynamic database of the Al-Co-Cr-Fe-Ni system was then obtained via extrapolation. The current Al-Co-Cr-Fe-Ni thermodynamic database enables us to carry out the calculations of phase diagrams, which can be used as useful guidelines to identify the Al-Co-Cr-Fe-Ni HEAs with desirable microstructures. In the fourth task, we discuss how as-cast and homogenized phases can be identified, what phases are usually found in the as-cast and homogenized conditions, and what the thermodynamics and kinetics of phase transformations are in the AlCoCrFeNi HEA. The microstructure and phase composition were studied in as-cast and homogenized conditions. It showed the dendritrical structure in the as-cast condition consisting primarily of a nano-lamellar mixture of A2 [disorder body-centered-cubic (BCC)] and B2 (ordered BCC) phases, in addition to a very small amount of A1 [disorder face-centered-cubic (FCC)] phases. The homogenization heat treatment resulted in an increase in the volume fraction of the A1 phase and formation of a Sigma phase. Tensile properties in as-cast and homogenized conditions are reported at 700 °C. Thermodynamic modeling of non-equilibrium and equilibrium phase diagrams for the AlCoCrFeNi HEA gave good agreement with the experimental observations of the phase contents. The reasons for the improvement of ductility after the heat treatment are discussed.

Download or read book Effects of Radiation on Materials written by Roger E. Stoller and published by ASTM International. This book was released on 1992 with total page 1315 pages. Available in PDF, EPUB and Kindle. Book excerpt: Symposium held in Nashville, Tennessee, June 1990. Almost two-thirds of these 91 papers are authored by researchers outside of the US (including information on research in the former USSR, Japan, and Europe). Topics include: current commercial power reactor systems; microstructural characterization

Download or read book Irradiation Effects on Structural Alloys for Nuclear Reactor Applications written by A. L. Bement and published by ASTM International. This book was released on 1971 with total page 571 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book High Entropy Alloys written by Michael C. Gao and published by Springer. This book was released on 2016-04-27 with total page 524 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a systematic and comprehensive description of high-entropy alloys (HEAs). The authors summarize key properties of HEAs from the perspective of both fundamental understanding and applications, which are supported by in-depth analyses. The book also contains computational modeling in tackling HEAs, which help elucidate the formation mechanisms and properties of HEAs from various length and time scales.

Download or read book Effects of Radiation on Materials written by and published by ASTM International. This book was released on with total page 767 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Materials Design for Advanced Nuclear Energy Systems written by Samuel W. McAlpine and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advanced nuclear reactors present a multitude of materials challenges due to high operating temperatures, corrosive environments, and neutron radiation damage. In this thesis, I focus on two approaches to designing better materials for advanced reactors, high entropy alloys (HEAs) and metallic multilayer composites (MMLCs). HEAs are chemically disordered solid solutions combining 4-5 or more elements, which of- ten have superior mechanical properties and radiation damage tolerance compared to advanced steels and Ni-base alloys. While HEAs have garnered immense attention within the research community, there is still no effective approach for predicting which compositions will tend to form a single phase microstructure. I develop an atomistic thermodynamic model which uses a quantity I coin as the atomistic mixing energy (AME) to understand phase stability in HEAs and predict which elements are more or less favored to mix within a given HEA system. The model also facilitates the correct calculation of the vacancy formation energy distribution in HEAs which gives insight to radiation damage, solid-state diffusion, and other vacancy-driven material behavior. To test the validity of the model, I synthesize and characterize 5 refractory HEA compositions: NbMoTaTiW, NbMoTaTiV, NbMoTaTiZr, NbMoTaHfW, and WTaVTiCr. Implications for single phase HEA design utilizing the model developed in this thesis are explored. The final part of the thesis focuses on MMLCs, in which different material functionalities are separated into different layers. Currently, few studies have aimed to understand radiation damage effects at the interface between different layers. I use interfacial self-ion irradiation along the bimetal interface within 2 MMLC systems to shed light on the radiation damage behavior of the interfacial region. Radiation--enhanced diffusion was observed in one MMLC, and a Cr-rich phase is observed along the interface in both MMLCs. The propensity for radiation-enhanced diffusion is related to the compositional gradient across the interface, while the Cr-rich interfacial phase could potentially lead to material embrittlement within MMLCs.

Download or read book Effects of Radiation on Materials written by Arvind S. Kumar and published by ASTM International. This book was released on 1994 with total page 1319 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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.

Download or read book Kate and Rosalind Or Early Experiences written by and published by . This book was released on 1853 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dual phase Materials in the Medium and High Entropy Alloy Systems Al Cr Fe Ni and Al Co Cr Fe Ni written by Ulrike Hecht and published by Frontiers Media SA. This book was released on 2021-08-25 with total page 133 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Evaluation on the Effect of Composition on Radiation Hardening and Embrittlement in Model FeCrAl Alloys written by and published by . This book was released on 2015 with total page 41 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report details the findings of post-radiation mechanical testing and microstructural characterization performed on a series of model and commercial FeCrAl alloys to assist with the development of a cladding technology with enhanced accident tolerance. The samples investigated include model alloys with simple ferritic grain structure and two commercial alloys with minor solute additions. These samples were irradiated in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL) up to nominal doses of 7.0 dpa near or at Light Water Reactor (LWR) relevant temperatures (300-400 C). Characterization included a suite of techniques including small angle neutron scattering (SANS), atom probe tomography (APT), and transmission based electron microscopy techniques. Mechanical testing included tensile tests at room temperature on sub-sized tensile specimens. The goal of this work was to conduct detailed characterization and mechanical testing to begin establishing empirical and/or theoretical structure-property relationships for radiation-induced hardening and embrittlement in the FeCrAl alloy class. Development of such relationships will provide insight on the performance of FeCrAl alloys in an irradiation environment and will enable further development of the alloy class for applications within a LWR environment. A particular focus was made on establishing trends, including composition and radiation dose. The report highlights in detail the pertinent findings based on this work. This report shows that radiation hardening in the alloys is primarily composition dependent due to the phase separation in the high-Cr FeCrAl alloys. Other radiation induced/enhanced microstructural features were less dependent on composition and when observed at low number densities, were not a significant contributor to the observed mechanical responses. Pre-existing microstructure in the alloys was found to be important, with grain boundaries and pre-existing dislocation networks acting as defect sinks, resulting in variations in the observed microstructures after irradiation. Dose trends were also observed, with increasing radiation dose promoting changes in the size and number density of the Cr-rich ' precipitates. Based on the microstructural analysis, performed tensile testing, and prior knowledge from FeCr literature it was hypothesized that the formation of the Cr-rich ' precipitates could lead to significant radiation-induced embrittlement in the alloys, and this could be composition dependent, a result which would mirror the trends observed for radiation-induced hardening. Due to the limited database on embrittlement in the FeCrAl alloy class after irradiation, a series of radiation experiments have been implemented. The overarching point of view within this report is the radiation tolerance of FeCrAl is complex, with many mechanisms and factors to be considered at once. Further development of the FeCrAl alloy class for enhanced accident tolerant applications requires detailed, single (or at least limited) variable experiments to fully comprehend and predict the performance of this alloy in LWRs. This report has been submitted as fulfillment of milestone M2FT-15OR0202321 titled, Summary report on the effect of composition on the irradiation embrittlement of Gen 1 ATF FeCrAl for the Department of Energy Office of Nuclear Energy, Advanced Fuel Campaign of the Fuel Cycle R & D program.

Download or read book Ab Initio Based Modeling of Radiation Effects in Multi Component Alloys written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The project began March 13, 2006, allocated for three years, and received a one year extension from March 13, 2009 to March 12, 2010. It has now completed 48 of 48 total months. The project was focused on using ab initio methods to gain insights into radiation induced segregation (RIS) in Ni-Fe-Cr alloys. The project had the following key accomplishments Development of a large database of ab initio energetics that can be used by many researchers in the future for increased understanding of this system. For example, we have the first calculations showing a dramatic stabilization effect of Cr-Cr interstitial dumbbells in Ni. Prediction of both vacancy and interstitial diffusion constants for Ni-Cr and Ni-Fe for dilute Cr and Fe. This work included generalization of widely used multifrequency models to make use of ab initio derived energetics and thermodynamics. Prediction of qualitative trends of RIS from vacancy and interstitial mechanisms, suggesting the two types of defect fluxes drive Cr RIS in opposite directions. Detailed kinetic Monte Carlo modeling of diffusion by vacancy mechanism in Ni-Cr as a function of Cr concentration. The results demonstrate that Cr content can have a significant effect on RIS. Development of a quantitative RIS transport model, including models for thermodynamic factors and boundary conditions.

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 High throughput Screening of High entropy Alloys for Advanced Nuclear Applications written by Michael Joseph Moorehead and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: New materials, including high-entropy alloys (HEAs), are being investigated to satisfy demandingrequirements for next-generation nuclear reactors. Unfortunately, the alloy discovery and development process for nuclear materials is prohibitively slow, even relative to other industries. This work covers the development and application of new high-throughput techniques to synthesize, irradiate, and characterize novel alloys for such applications. Using a LENS MR-7 directed energy deposition (DED) 3D metal printer, a process is developed in which alloys of arbitrary compositions are rapidly produced in regular arrays of "bulk" coupons. These compositional arrays have been heat treated and mechanically polished in parallel before being irradiated with heavy ions at the University of Wisconsin-Madison Ion Beam Laboratory (IBL). To accommodate the large sample arrays, an automated high-throughput irradiation system was developed and installed in the IBL, equipped with an IR laser to locally heat individual samples, which has since been used to irradiate nearly 100 samples to end-of-life damage levels for core components in proposed advanced reactors. Using automated nanoindentation and optical profilometry, the hardening and swelling of many Cr-Fe-Mn-Ni HEAs has been measured and trends in the irradiation response as a function of composition are examined. Of the elements in the Cr-Fe-Mn-Ni system, Cr and Ni appear to affect the swelling behavior most predominantly, with swelling increasing monotonically with increasing Cr concentration while swelling increases with Ni concentration up to ~30 at% before rapidly dropping with continued Ni additions until approaching pure Ni. Trends in swelling behavior are in good agreement with previous ion irradiation studies of Cr-Fe-Ni alloys in literature, which also serves to validate the overall high-throughput methodology employed in this work. Using the techniques described herein, immense time savings over traditional techniques are realized such that a single compositional array of 25 alloy coupons can by synthesized, heat treated, mechanically polished, irradiated, and characterized in less than a week

Download or read book Defect Properties in High Entropy Alloys from Atomistic Calculations and Machine Learning written by Gaurav Arora and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the past decade, high entropy alloys (HEAs) have gathered extensive attention due to their exceptional mechanical properties. The properties include thermal stability, improved fatigue, and fracture properties, high strength to elastic ratio, improved high temperature and irradiation properties, exceptional elastic properties at cryogenic temperature, and outstanding corrosion resistance that make these alloys potential candidates for future structural, nuclear, and high- temperature applications. HEAs consist of multiple principal elements that are randomly distributed on a crystal lattice. Elements are usually present in equi-atomic or nearly equi-atomic ratios. The presence of multiple principal elements provides an opportunity to explore huge phase space for designing novel HEA to be used for different applications. However, conventional computational tools such as atomistic simulations and density functional theory (DFT) which have been proven to be effective for studying and designing dilute alloys cannot be applied seamlessly to the HEAs due to inherent complexity. Therefore, other techniques such as machine learning (ML) must be applied to explore the huge phase space provided by HEAs. In this work, we have used various ML techniques including deep neural network (DNN) to predict different defect properties for HEAs. First, we have developed a bond-length based framework using data collected from atomistic simulation in conjunction with ML for predicting stacking fault energy (SFE) in Ni-Fe, Ni-Cr, and Fe-Cr alloy systems. For further exploration, SFE is predicted in various alloys using DFT and ML. We explored the effect of charge density on SFE and used it as a key quantity to predict SFE in ML. Further, we explored the charge density distortion using an image-recognition method. We used convolutional neural network (CNN) to analyze and learn patterns of charge density images. Point defect properties such as formation energy, segregation energy, and migration barrier of dopants at the grain boundaries are also studied. Finally, we also studied the effect of composition on the irradiation induced defects such as voids. Overall, this work advances the understanding of SFE and different ML techniques which could be used for expediting the design and discovery of new HEAs.

Download or read book Modeling Defect Cluster Evolution in Irradiated Structural Materials written by and published by . This book was released on 2015 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: Exposure of metallic structural materials to irradiation environments results in significant microstructural evolution, property changes, and performance degradation, which limits the extended operation of current generation light water reactors and restricts the design of advanced fission and fusion reactors. Further, it is well recognized that these irradiation effects are a classic example of inherently multiscale phenomena and that the mix of radiation-induced features formed and the corresponding property degradation depend on a wide range of material and irradiation variables. This inherently multiscale evolution emphasizes the importance of closely integrating models with high-resolution experimental characterization of the evolving radiation-damaged microstructure. Lastly, this article provides a review of recent models of the defect microstructure evolution in irradiated body-centered cubic materials, which provide good agreement with experimental measurements, and presents some outstanding challenges, which will require coordinated high-resolution characterization and modeling to resolve.