Symposium Organizers
Gianguido Baldinozzi, Paris-Saclay University
David Andersson, Los Alamos National Laboratory
Chaitanya S. Deo, Georgia Institute of Technology
Michael R. Tonks, Pennsylvania State University
MD8.1: Modeling Radiation Effects at Multiple Scales
Session Chairs
Chaitanya Deo
Meimei Li
William Weber
Tuesday PM, March 29, 2016
PCC West, 100 Level, Room 106 BC
2:30 PM - *MD8.1.01
Coupling Lattice Kinetic Monte Carlo and Phase Field for Solute Precipitation in RPV Steels
Yongfeng Zhang 1,Daniel Schwen 1,Xianming Bai 1,Benjamin Spencer 1
1 Idaho National Lab Idaho Falls United States,
Show AbstractPredicting the performance of reactor pressure vessels (RPVs) is challenging as the physics required spans multiple length and time scales. Utilizing multiscale modeling and simulations, the Grizzly project aims to describe the microstructure evolution, the consequent property degradation, and the performance of RPVs under various loading scenarios. In this talk, multiscale modeling under the Grizzly project by coupling lattice kinetic Monte Carlo and phase field for solute precipitation will be presented. Here, we use lattice kinetic Monte Carlo to describe precipitate nucleation, and phase field for subsequent coarsening. Atomistic simulations such as molecular dynamics simulations are also involved to obtain necessary parameters and mechanisms for the effects of extended lattice defects on Cu precipitation. The information of precipitation including the volumetric density and size distribution of precipitates will be used in crystal plasticity and fracture mechanics to evaluate the hardening and embrittlement. The precipitation kinetics of Cu in the Fe-Cu1.34% alloy has been benchmarked with thermal aging experiments.
3:00 PM - MD8.1.02
Multiscale Material Model Development and Simulations for Accident Tolerant Fuels
Jianguo Yu 1,Jason Hales 1
1 Idaho National Lab Idaho Falls United States,
Show AbstractUse of uranium–silicide (U-Si) in place of uranium dioxide (UO2) is one of the promising concepts being proposed to increase the accident tolerance of nuclear fuels. This is due to a higher thermal conductivity than UO2 that results in lower centerline temperatures. U-Si also has a higher fissile density, which may enable some new cladding concepts that would otherwise require increased enrichment limits to compensate for their neutronic penalty. However, many critical material properties for U-Si have not been determined experimentally. It is anticipated that modeling and simulation may deliver guidance on the importance of various properties and help prioritize experimental work. In this talk, we will present our recent progress on multiscale material model development for accident tolerant fuels, spanning density functional theory calculations, molecular dynamics potential development, phase field simulation and engineering scale modeling. Our ultimate goal is to develop knowledge-based models for use at the engineering scale with a minimum of empirical parameters.
3:15 PM - *MD8.1.03
Phase-Field Modeling of Irradiation Induced Microstructures
David Simeone 2,Laurence Luneville 2,Gilles Demange 2,Vassilis Pontikis 1
2 SPMS, LRC Carmen Centralesupelec Chatenay-Malabry France,3 DM2S, SERMA CEA Gif-sur-Yvette France,2 SPMS, LRC Carmen Centralesupelec Chatenay-Malabry France1 DMN, SRMA, LRC Carmen CEA Gif-sur-Yvette France,2 SPMS, LRC Carmen Centralesupelec Chatenay-Malabry France4 DSM, Iramis, LSI CEA Gif-sur-Yvette France,1 DMN, SRMA, LRC Carmen CEA Gif-sur-Yvette France
Show AbstractIn this work irradiation-induced phase separation and the resulting microstructures are obtained via the combination of Phase Field (PF) modeling with atomistic Monte Carlo simulations in the pseudo-grand canonical ensemble (GCMC). The last allow for calculating the equilibrium phase diagram of the silver-copper alloy, chosen as a model of binary systems with large miscibility gap and, for extracting the parameters of the excess free-energy PF functional [1]. Relying on this methodology, the equilibrium phase diagram of the alloy is predicted in excellent agreement with the experiment whereas, under irradiation, the predicted microstructures are functions of the irradiation parameters. Different irradiation conditions result in various microstructures, which are conveniently represented as an out of equilibrium “phase diagram” in view to facilitate the comparison between modeling and experiment.
[1] L. Luneville, G. Demange, V. Pontikis, D. Simeone, Mater. Res. Soc. Symp. Proc. 1743 (2015), DOI: 10.1557/opl.2015.360
3:45 PM - MD8.1.04
Multiscale Approach to Predict the Ageing and Strengthening of Cu-Alloyed α-Iron Under Service Conditions
Siegfried Schmauder 1,David Molnar 3,Peter Binkele 1,Ulrich Weber 2,Dennis Rapp 1
1 Institute for Materials Testing, Materials Science and Strength of Materials (IMWF), University of Stuttgart Stuttgart Germany,3 formerly at IMWF, University of Stuttgart Stuttgart Germany2 Materials Testing Institute (MPA), University of Stuttgart Stuttgart Germany
Show AbstractPipe steels used in thermal power plants are subject to harsh thermal conditions during their service life. This often includes continuous exposure to steam at temperatures above 300°C. Under these conditions the microstructure of the materials used for pipes (Copper-alloyed steels) undergoes accelerated thermal ageing. The dissolved Cu-atoms organize in the form of steadily growing precipitates. This precipitation alters the material's structural properites by affecting the mobility of dislocations, resulting in precipitation hardening in the case of reduced dislocation mobility. On the other hand this hardening also influences the failure behavior of the pipes which can lead to sudden failure in the piping system if not accounted for.
To investigate these effects, a multiscale approach is applied to simulate the various proccesses involved in age hardening under thermal loading. In this multiscale approach each process is investigated at it's appropiate length and time scale. The methods include kinetic monte carlo (KMC) simulations to model the time and temperature dependent precipitation process, molecular dynamics (MD) simulations to analyze the influence of individual precipitates on passing dislocations, discrete dislocation dynamics (DDD) simulations for assessing the hardening caused by different precipitate distributions and sizes and finally finite element method (FEM) simulations to model the macroscopic failure process. Each of the four methods mentioned here depends on input parameters from a previous simulation (sequential multiscaling). The KMC method relies on energies derived from ab-initio calculations. It's output is used for the DDD simulation of real precipitate-dislocation interactions, where the interaction strength comes from MD simulations. The simulation of macroscopic damage using FEM uses material parameters from the DDD results, which mainly consist of stress-strain curves and the change thereof with different precipitation stages and alloying compositions.
The predicted behavior of the materials investigated was also compared with experimental results at different ageing times. It could be shown that the predictions match the expected behavior quite well. This methodology provides the means to investigate other precipitation hardening affected alloys and to be used in parameter studies for understanding and possibly optimizing the mechanical properties of alloys.
MD8.2: Metallic Systems I
Session Chairs
Chaitanya Deo
Yongfeng Zhang
Tuesday PM, March 29, 2016
PCC West, 100 Level, Room 106 BC
4:30 PM - *MD8.2.01
Materials in Harsh Environments: Insights from Atomic Scale Simulations
Susan Sinnott 1
1 Pennsylvania State Univ University Park United States,
Show AbstractA driving force for research is the discovery and design of new materials to improve existing technologies or enable new applications. Material modeling methods are now widely applied in pursuit of this objective. This presentation will review the evolution of some common material modeling methods and their integration with cutting-edge experimental techniques. Illustrative applications will be discussed within the context of materials used in harsh environments, including materials associated with nuclear fuel reactors and materials exposed to acid gases.
5:00 PM - MD8.2.03
Spall Response of Single and Nanocrystalline Tantalum at Extreme Strain-Rates
Eric Hahn 2,Tane Remington 1,Shiteng Zhao 1,Eduardo Bringa 3,Timothy Germann 2,Marc Meyers 1
1 University of California San Diego La Jolla United States,2 Los Alamos National Laboratory Los Alamos United States,1 University of California San Diego La Jolla United States3 National University of Cuyo Mendoza Argentina2 Los Alamos National Laboratory Los Alamos United States
Show AbstractStrain-rate and microstructure play a significant role in the mechanical response of metals. Predictions based on traditional theory suggest that, as strain-rate increases, compressive and tensile strength should increase accordingly. Recent experimental results and theoretical multiscale models suggest that, during high strain-rate compression, grain size has a negligible effect on the ensuing plastic flow dynamics. During tension however, as grain size decreases, tensile strength may decrease due to an increased propensity to fail at grain boundaries. Using non-equilibrium molecular dynamics simulations we characterize the ductile tensile failure of single and nanocrystalline tantalum over six orders of magnitude in strain-rate. This comparison is extended to over nine orders of magnitude including experimental results from resent laser shock campaigns. Spall strength primarily follows a power law dependence with strain-rate over this extensive range. In all cases, voids nucleate heterogeneously at material defects. Importantly, strain-rate and grain size dictate void nucleation sites and the resulting void growth kinetics by altering the type and density of available defects: vacancies, dislocations, deformation twins, and grain boundaries.
5:15 PM - *MD8.2.04
Understanding Radiation Damage and Deformation Dynamics in Neutron-Irradiated Steels with High-Energy X-Rays
Meimei Li 1,Jonathan Almer 1,Xuan Zhang 1,Chi Xu 1,Yiren Chen 1,Jun-Sang Park 1,Peter Kenesei 1,Hemant Sharma 1,Yong Yang 2,Lizhen Tan 3
1 Argonne National Lab Lemont United States,2 University of Florida Gainesville United States,1 Argonne National Lab Lemont United States2 University of Florida Gainesville United States3 Oak Ridge National Lab Oak Ridge United States
Show AbstractThis paper will present recent results of in situ straining experiments with concurrent wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS), and ex situ 3D far-field high-energy X-ray diffraction microscopy (ff-HEDM) of neutron-irradiated ferritic and austenitic steels. High-energy X-rays offer new opportunities for probing mm-sized specimens exposed to external stimulants, e.g. stress, temperature, with multiple probes, which allow characterization of microstructural features ranging from the nano-scale to microscale, linked directly with the macroscale stress-strain behavior of a bulk material. The combination of in situ straining/annealing experiments with HEDM allows investigation of microstructural evolution and plastic deformation processes at the grain scale, providing a detailed knowledge of key physical mechanisms such as recrystallization and grain growth kinetics, elastic strain, dislocation structure and substructure dynamics, grain rotation during deformation, and defect recovery. This information is crucial to the understanding of the effect of microstructural inhomogeneities on the macroscopic behavior of the polycrystalline aggregate, and the development of microstructure-sensitive models for predictions of the performance, degradation and lifetimes of nuclear components. This talk will discuss the current capability of in situ straining/annealing and ex situ 3D characterization of neutron-irradiated specimens, and the outlook for in situ time- and spatial- resolved (4D) characterization of grain dynamics in irradiated materials with high-energy X-rays.
Symposium Organizers
Gianguido Baldinozzi, Paris-Saclay University
David Andersson, Los Alamos National Laboratory
Chaitanya S. Deo, Georgia Institute of Technology
Michael R. Tonks, Pennsylvania State University
MD8.3/EE12.2/EE13.2: Joint Session: Actinide Materials—Radiation Damage
Session Chairs
Gianguido Baldinozzi
Thibault Charpentier
Blas Uberuaga
Gary Was
Wednesday AM, March 30, 2016
PCC West, 100 Level, Room 106 BC
9:30 AM - *MD8.3.01/EE12.2.01/EE13.2.01
Ion Irradiation for Studying Multiscale Radiation Effects in Structural Materials and Fuels
Gary Was 1,Jian Gan 2
1 University of Michigan Ann Arbor United States,2 Idaho National Laboratory Idaho Falls United States
Show AbstractUnderstanding the evolution of microstructures in irradiated materials is key to both the prediction of their future behavior and the development of advanced, radiation tolerant materials. Well controlled and carefully tailored ion irradiation has been successful at creating most of the features as well as their time and spatial evolution in LWR core structural materials such as stainless steels and zirconium alloys, and in fast reactor candidate materials such as ferritic-martensitic steels. Evolution of defect cluster distribution, loop size distribution, precipitate formation and growth, segregation to interfaces, and void nucleation and growth have all been captured using ion irradiation. The co-implantation of He to simulate transmutation is important in the procssess of void nucleation and growth, and co-injection of H accounts for uptake from the water in LWR components. Such techniques can also be applied to fuels in which fission gasses combine with radiation damage to play a key role in the evolution of microstructure and mechanical properties. This talk will focus on the application of carefully tailored ion irradiation as a means of capturing the multiscale nature of radiation effects in actinides.
10:00 AM - MD8.3.02/EE12.2.02/EE13.2.02
Radiation Induced Fission Gas Diffusion in UO2
Michael Cooper 2,David Andersson 2,Patrick Burr 1,Navaratnarajah Kuganathan 1,Michael Rushton 1,Robin Grimes 1,James Turnbull 3,Christopher Stanek 2
2 Materials Science and Technology Division Los Alamos National Laboratory Los Alamos United States,1 Materials Imperial College London London United Kingdom3 Independent Advisor London United Kingdom
Show AbstractThe release of fission gases during normal and accident conditions is of key importance for the safe operation of nuclear fuel. The release of fission gas can result in over pressurization of the fuel clad and can alter heat transfer from the fuel. At lower temperatures, such as those in the periphery of the pellet, the gas diffusivity is found to be athermal and is said to be driven by damage cascades. In fact, it is shown experimentally to be proportional to the fission rate. Underpinning this behavior are atomic scale processes that can be investigated through molecular dynamics. Firstly, potential parameters are developed for Xe and Kr that are consistent with a previously developed manybody potential for UO2 by force matching between molecular dynamics and density functional theory. Subsequently, we investigate the mobility of fission gases, Xe and Kr, during radiation damage cascades. By examining the effect of PKA energy and of multiple cascades occurring on the same region of crystal we attempt to link individual damage cascade simulations to the experimentally determined relationship between fission rate and gas diffusivity.
10:15 AM - MD8.3.03/EE12.2.03/EE13.2.03
Small Angle X-Ray Scattering Study of Helium Bubbles in Plutonium
Anthony Van Buuren 1,Jason Jeffries 1,Trevor Willey 1,Mark Wall 1,Jan Ilavsky 2
1 Lawrence Livermore National Lab Livermore United States,2 APS Argonne National Laboratory Argonne United States
Show AbstractThe evolution of inert gas bubbles in metals has important implications on the evolution of the mechanical properties of nuclear materials as well as materials in highly irradiating environments, such as those expected in next-generation nuclear reactors. The presence of gas bubbles in metallic lattices can profoundly alter the mechanical properties and strength of materials leading to embrittlement, swelling, and blistering. The behaviors of gas bubbles are thus important components of any evaluation of the effects of irradiation-induced aging in a material. The alpha decay of plutonium in PuGa alloys continually generates inert He atoms within the lattice of the PuGa matrix. In naturally aged Pu specimens, those He atoms form into bubbles, He-filled vacancy clusters, with a characteristic size from 2-10nm. Upon annealing, the He bubbles are subject to temperature induced changes which results in a coarsening of the bubble distribution yielding a lower bubble density but larger average bubble sizes up to 60nm. The formation of the He bubbles in PuGa alloys has been studied by TEM however concern has been raised that the preparation of very thin samples (> 1 micron) needed in the TEM experiment together with low number of voids in any particular TEM images may skew the measured He bubble concentration and distribution. To resolve these outstanding issues we have used a combination SAXS and USAXS to examine the formation and growth of He bubbles in aged and temperature annealed PuGa alloys. Development of non destructive volumetric probes for nuclear materials is needed to confirm TEM results and validate models of Pu aging.
10:30 AM - *MD8.3.04/EE12.2.04/EE13.2.04
He Bubble Structure Evolution and Effect on the Mechanical Properties of Metals Studied Using Novel Microscopy Techniques
Peter Hosemann 1,Zhangjie Wang 2,Frances Allen 1,David Frazer 1,Mehdi Balooch 1
1 Nuclear Engineering University of California-Berkeley Berkeley United States,1 Nuclear Engineering University of California-Berkeley Berkeley United States,2 State Key Laboratory for Mechanical Behavior of Materials Jiaotong University Xi'an China
Show AbstractThe materials deployed in many nuclear applications suffer from the buildup of helium generated as a result of neutron bombardment. Typically the He is not soluble in the target material and forms nano-sized bubbles within it. Due to the fact that studying the buildup of He bubbles in actual active materials is obviously difficult, surrogate materials and He implantation studies are utilized to understand the underlying effects. In this work we utilize the new ORION Nanofab, an He/Ne and Ga ion beam microscope, to implant He into Cu to develop an understanding of the formation of the He bubble superlattices and their effect on the mechanical properties of the material. In situ TEM nanocompression tests are performed to quantify the changes in the mechanical properties and to observe the evolution of the He bubble structure under stress. In addition, we present first results from correlative microscopy of the He implanted surfaces.
11:00 AM - MD8.3/EE12.2/EE13.2
BREAK
11:30 AM - *MD8.3.05/EE12.2.05/EE13.2.05
Radiation Damages in Nuclear Waste Glasses: An NMR Point of View
Thibault Charpentier 2,Sylvain Peuget 1,Alexandre Le Gac 3,Bruno Boizot 3,Cindy Rountree 4,Laura Martel 5,Joseph Somers 5
2 CEA, IRAMIS, NIMBE - UMR CEA-CNRS 3685 Gif-sur-Yvette France,1 CEA, DEN, LMPA Bagnols-sur-Cèze France1 CEA, DEN, LMPA Bagnols-sur-Cèze France,3 CEA, IRAMIS, LSI Gif-sur-Yvette France3 CEA, IRAMIS, LSI Gif-sur-Yvette France4 CEA, IRAMIS, SPEC - UMR CEA-CNRS 3680 91191 Gif-sur-Yvette France5 Institute for Transuranium Elements (ITU) European Commission, Joint Research Centre (JRC) 76125 Karlsruhe Germany
Show AbstractBorosilicate glasses have been recognized as valuable materials for the conditioning of nuclear wastes. An important issue for their long-term behaviour is radiation effects which may impact their performance and stability. To address these concerns, a fundamental understanding of the origin at the atomic scale of the macroscopic property evolutions must be established. Over the last decade, magic-angle spinning nuclear magnetic resonance (MAS NMR) has firmly established itself as one of the most powerful tool to investigate a glass’s structure. It offers several probes of the local structure, nuclei such as 11B, 23Na, 27Al, 29Si and 17O, to probe changes either in the glass network or in the alkali distribution.
Recently, using external heavy ions irradiation (Xe, Au, Kr) to simulate alpha decays,[1-3] dramatic changes in the local network structure were evidenced : conversion of tetrahedral BO4 units into planar trigonal BO3 units (11B), appearance of high-coordination aluminum units (AlO5, AlO6); glass depolymerisation (29Si) and changes in the distribution of alkali cations (23Na). Additionally, the spectra broaden globally which supports the hypothesis of an increased topological disorder after irradiation. All these structural changes are similar to those observed with increasing the glass temperature or quenching rate and support therefore the model of ballistic disordering fast quenching events which induce a new glassy state with higher fictive temperature. Effects of external electronic (beta) irradiations will be also discussed. If NMR spectra variations show similar trends -but much less pronounced- they are mainly engendered by alkali migration phenomena and formation of molecular oxygen.
Until recently, these studies were limited to externally irradiated samples (enabling the different components of irradiation to be dissociated for their precise investigation), but recently, the first MAS-NMR experiments could be performed on radioactive glasses (doped with 244Cm 0.1 % mol.) paving the way for future MAS NMR examinations of self-irradiation damages in glasses. Experiments were performed at the Joint Research Centre Institute for Transuranium Elements (JRC-ITU) where a commercial NMR spectrometer were integrated with a radioactive glovebox and a MAS commercial probe. First results will be presented. Competitive effects between the recoil nuclei and alpha decays were evidenced and the high resistance of the nuclear waste glasses corroborated.
[1] S. Peuget, C. Mendoza, E.A. Maugeri et al. Procedia Materials Science 7, (2014) 252-261
[2] C. Mendoza, S. Peuget, T. Charpentier et al., Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms 325 (2014) 5-65
[3] S. Peuget, E.A. Maugeri, T. Charpentier et al. J. Non-Cryst. Solids 378 (2013) 201-212.
12:00 PM - MD8.3.06/EE12.2.06/EE13.2.06
Effects of Radiation Fields on Actinide-Containing Materials
Steven Conradson 1,Janne Pakarinen 2,Mahima Gupta 3,Akhil Tayal 1
1 Soleil Saint-Aubin - BP48 France,2 Belgian Nuclear Research Centre Mol Belgium3 Morpho Detection Fremont United States
Show AbstractBecause of their internal radiation and their applications, nuclear materials are often subject to extreme radiation fields that affect their structures and properties over time. In plutonium, every atom is displaced from its lattice position once every ten years on average. Although almost all of the displaced nuclei rapidly return to the lattice quickly, some do not, becoming defects in the material. The conventional idea is that these will accumulate randomly, causing increasing disorder in the material that will eventually result in its becoming amorphous. Alternatively, these defects might interact strongly with each other and other defects or inhomogeneities in the material. If they do then the possibility exists that they will stabilize themselves and aggregate into defect-enriched domains until these move so far away from the original composition that they could potentially transofrm into domains with altered structures that are still trapped in the host lattice. This process describes the formation of helium bubbles from the emitted alpha particles, but also other such nanometer and larger scale structures. We have now observed exactly this type of phenomenon in delta plutonium-gallium alloys and also in ion irradiated uranium dioxide. Although delta plutonium eventually succumbs to accumulated radiation damage and does lose order, prior to that stage it displays a cycle based on the formation of particular locally ordered structures that deviate from the fcc one that is its long range average. These alternative structures are similar to the ones observed in new materials that are caused by strong interactions between the alloys atoms that cause it to cluster to form a quasi-intermetallic. Similarly, the propensity of adventitious O to cluster in uranium dioxide is emulated as the result of ion irradiation. Uranyl type species with higher valences are observed just as with oxidation to mixed valence compounds, although in the case of ion irradiation they must be mirrored by lower valence species as well. This complication demonstrates the substantial stability of these non-equilibrium structures. In the case of radiation damage, and also other forms of aging, this phenomenon of the formation of structures on increasingly large length scales is, in fact relatively common. The formation of these structures is coupled with the irreversibility of damage accumulation, with the formation of such structures corresponding to phase transtions. Aging effects may therefore be best described as non-equilibrium thermodynamic processes with these irreversible steps corresponding to critical points on the path.
12:15 PM - MD8.3.07/EE12.2.07/EE13.2.07
How Well Can Electronic Structure Calculations Describe Uranium Dioxide Properties
Marjorie Bertolus 1,Michel Freyss 1,Ram Devanathan 2,Matthias Krack 3
1 CEA, DEN St Paul-Lez-Durance France,2 Pacific Northwest National Laboratory Richland United States3 Paul Scherrer Institute Villigen PSI Switzerland
Show AbstractOne challenge for the development of Gen IV nuclear reactors is to improve significantly the effectiveness of the design and selection of innovative fuels. To this aim, multiscale modelling approaches are developed to build more physically based kinetic and mechanical mesoscale models to enhance the predictive capability of fuel performance codes. Atomic scale methods, in particular electronic structure calculations, form the basis of this multiscale approach. It is therefore essential to know the accuracy of the results computed at this scale if we want to feed them into higher scale models.
Electronic structure calculation methods, especially density functional theory (DFT), have been used extensively on molecular and solid systems during the last thirty years. Numerous assessments of these methods have been performed, which show that they are powerful tools yielding precise and predictive results for a large number of solid and molecular systems, therefore contributing to the understanding of numerous phenomena. The application to nuclear materials under irradiation and especially to fuels, however, is more delicate and calls for bespoke developments. A specific assessment of the atomic scale methods for the description of nuclear fuel under irradiation is therefore necessary.
We will present the result of the extensive assessment effort of the results of state-of-the-art electronic calculations on uranium dioxide performed in the framework of the Working Party on Multiscale Modelling of Fuels and Structural Materials for Nuclear Systems (WPMM) of the OECD/NEA.
12:30 PM - MD8.3.08/EE12.2.08/EE13.2.08
Development of a Multiscale Thermal Conductivity Model for Fission Gas in UO2
Michael Tonks 1,Xiang-Yang Liu 2,David Andersson 2,Aleksandr Chernatynskiy 3,Giovanni Pastore 4,Christopher Stanek 2
1 Pennsylvania State Univ University Park United States,2 Los Alamos National Laboratory Los Alamos United States3 Missouri Institute of Science and Technology Rolla United States4 Idaho National Laboratory Idaho Falls United States
Show AbstractModels used in fuel performance codes to predict the change in the fuel thermal conductivity are typically empirical fits to experimental data, and are independent of other models such as fission gas or grain size. As part of the Nuclear Energy Advanced Modeling and Simulation program, we are developing a system of new materials models for fuel performance that are based on microstructure rather than burn-up, for use in Idaho National Laboratory’s (INL’s) BISON code. In order to obtain a mechanistic model of thermal conductivity, we have developed a preliminary model that couples the fission gas release model to the thermal conductivity. Atomistic and mesoscale simulations were used to quantify the impact of three distributions of fission gas on the thermal conductivity: dispersed gas atoms, small intragranular gas bubbles, and grain boundary bubbles. The model was implemented in BISON and the results were compared to reactor test data.
12:45 PM - MD8.3.09/EE12.2.09/EE13.2.09
Fission Gas Diffusion in UO2 Nuclear Fuel by Extended Vacancy Cluster
David Andersson 1,Romain Perriot 1,Michael Cooper 1,Xiang-Yang Liu 1,Giovanni Pastore 2,Michael Tonks 3,Blas Uberuaga 1,Christopher Stanek 1
1 Los Alamos National Laboratory Los Alamos United States,2 Idaho National Laboratory Idaho Falls United States3 Pennsylvania State University University Park United States
Show AbstractIn UO2 nuclear fuel, the retention and release of fission gas atoms such as xenon (Xe) are important for nuclear fuel performance. We use multi-scale simulations to determine fission gas diffusion mechanisms as well as the corresponding rates in UO2 under both intrinsic and irradiation conditions. Density functional theory (DFT) calculations are used to study formation, binding and migration energies of small clusters of Xe and vacancies. Empirical potential calculations enable us to determine the corresponding entropies and attempt frequencies for migration as well as investigate the properties of large clusters or small fission gas bubbles. A continuum reaction-diffusion model is developed for Xe and point defects based on the mechanisms and rates obtained from atomistic simulations. Effective fission gas diffusivities are then obtained by solving this set of equations for different chemical, irradiation and microstructure conditions using the MARMOT phase field code. Emphasis is put on understanding how the diffusion rates evolve as function of the irradiation dose and its coupling to defect concentrations and microstructure. The predictions are compared to available experimental data. The importance of the large XeU3O cluster (a Xe atom in a uranium + oxygen vacancy trap site with two bound uranium vacancies) is emphasized, which is a consequence of its high mobility and high binding energy. However, all simple vacancy-mediated diffusion mechanisms underestimate the Xe diffusivity compared to the empirical radiation-enhanced model used in most fission gas release models. We investigate the possibility that diffusion of small fission gas bubbles or extended Xe-vacancy clusters may be responsible for the radiation-enhanced diffusion coefficient. These studies highlight the importance of U divacancies and a cluster composed of an octahedron coordination of uranium vacancies encompassing a Xe fission gas atom. The latter cluster can migrate via a multistep mechanism with a low effective barrier.
MD8.4: Materials in Extreme Environments
Session Chairs
Donald Brown
Chaitanya Deo
Laurence Luneville
Wednesday PM, March 30, 2016
PCC West, 100 Level, Room 106 BC
2:30 PM - *MD8.4.01
The ANSTO/SINAP Joint Research Centre for Thorium Molten Salt Reactors, a Practical Example of the Multiscale Behavior of Materials in Extreme Environments
Gordon Thorogood 1,Massey de los Reyes 2,Rohan Holmes 1,Sachin Shrestha 1,Tracey Hanley 1,Michael Drew 1,Hefei Huang 3,Zhijun Li 3,Juan Hou 3,Ping Huai 3,Gregory Lumpkin 1,Paul Di Pietro 1
1 ANSTO Lucas Heights Australia,2 NFCRC Adelaide Australia3 SINAP Shanghai China
Show Abstract
During the 1960’s, at the Oak Ridge National Laboratory in the USA, the molten salt breeder reactor concept was developed. The 8 MW Molten Salt Reactor Experiment (MSRE) operated over four years to 1969 with the MSR programme running from 1957-1976. The initial programme from 1965-68 utilised uranium-235 tetrafluoride (UF4) fuel enriched to 33%. This was dissolved in a mixture of molten lithium, beryllium and zirconium fluorides which was heated to between 600-700°C and flowed through a graphite moderator at ambient pressure. The fuel was approximately one precent of the fluid with the secondary circuit being composed of lithium beryllium fluoride (FLiBe). With the completion of the UF4 programme, a second programme ran from 1968 to 1969 based on U-233 fuel - the reactor the first to do so. Thus this programme prepared the way to build a MSR breeder utilising thorium. This initial work demonstrated the feasibility of this system, which included online reprocessing, but also highlighted some corrosion and safety issues. Japan, Russia, China, France and the USA, are again interested in Molten Salt Reactors (MSR’s) and it is one of the six Generation IV designs selected for further development in two versions - the molten salt fast reactor (MSFR) and the Advanced High Temperature Reactor (AHTR). Since the Generation IV selection process significant design changes have occurred. The first goal is to produce a simpler MSR that does not breed fuel or perform online reprocessing. Currently researchers in the USA and at the Chinese Academy of Sciences/SINAP are working on solid fuel, salt-cooled reactor technology as a realistic first step into MSRs. Given the MSR may be applicable to the Australian environment, the Australian Nuclear Science and Technology Organisation (ANSTO) began a Joint Research Centre (JRC) with SINAP to investigate three aspects of the materials issues in relation to MSR’s. They were; a. radiation damage studies of nickel based alloys, b. molten salt corrosion of component materials and c. in-situ molten salt creep tests of nickel based alloys. This talk will summarise this two-year program and present the possible future actives of this JRC.
3:00 PM - MD8.4.02
Effects of Electronic Energy Loss on Evolution of Radiation Damage in Ceramics
William Weber 2,Eva Zarkadoula 2,Ritesh Sachan 2,Haizhou Xue 1,Ke Jin 2,Yanwen Zhang 2
1 University of Tennessee Knoxville United States,2 Oak Ridge National Laboratory Oak Ridge United States,2 Oak Ridge National Laboratory Oak Ridge United States1 University of Tennessee Knoxville United States
Show AbstractThe interaction of ions with solids results in energy loss to both atomic nuclei and electrons in the solid. Using experimental and computational approaches, we have investigated the separate and combined effects of nuclear and electronic energy loss on the response of ceramics to ion irradiation over a range of energies. Experimentally, ion mass and energy are used to control the ratio of electronic to nuclear energy loss; whereas, large scale molecular dynamics simulations, which include ballistic collision processes and the inelastic thermal spike from ionization, are used to model these effects. Using these approaches, we demonstrate additive effects of nuclear and electronic energy loss on damage production; competitive effects via ionization-induced damage recovery; synergistic effects on damage production; and a cross-over effect from competitive to synergistic in ion-irradiated ceramics. The latest results on these effects will be presented. These results have significant implications for the response of materials to extreme radiation environments and ion beam modification of materials to produce novel defect structures, nanostructures and phase transformations that tailor chemical and physical properties or create new functionalities within materials.
This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.
3:15 PM - MD8.4.03
In-Service Enhancement of Nuclear Nanoceramics
Francisco Garcia Ferre 1,Alexander Mairov 2,Luca Ceseracciu 1,Yves Serruys 3,Patrick Trocellier 3,Marco Beghi 4,Lucile Beck 3,Kumar Sridharan 2,Fabio Di Fonzo 1
1 Istituto Italiano di Tecnologia Milano Italy,2 University of Madison-Wisconsin Madison United States3 CEA Paris France4 Politecnico di MIlano Milano Italy
Show AbstractA long-standing challenge for the development of advanced nuclear systems is the lack of materials capable of withstanding the anticipated operating conditions and accident scenarios. Typically, nuclear materials are designed to an optimum before entering service. But during operation, the radiation environment inexorably shifts materials out of equilibrium, with a consequent deterioration of their mechanical performance and reliability. Here, we propose an alternative design strategy, and report on the enhancement in-service of the mechanical performance of an initially metastable oxide nanoceramic as radiation damage approaches the extreme. The enhancement observed is correlated to radiation-induced structural rearrangements, and is explained in terms of nanoscale energy dissipation mechanisms activated upon impact loading, including twinning and local amorphization. Lastly, we show a potential field of application of the oxide nanoceramic, namely as a coating for fuel cladding in future generation nuclear systems, and show that it successfully provides corrosion resistance at high temperature in chemically aggressive media –specifically, heavy liquid metals.
3:30 PM - *MD8.4.04
Unclear Nuclear Materials Development
Karl Whittle 1
1 University of Liverpool Liverpool United Kingdom,
Show AbstractThe future of nuclear materials development, for both fission and fusion designs, is complex with multiple factors. In many cases the material choices are limited, but it is often the cast the mateirals from one application can be used within another context, for example materials developed for use within a fission core as a fuel additive, can often have applications as a waste form. This talk will address the key factors defining the development of nuclear materials, which have use within extreme environments, such as high radiation fields, and discuss both carbides and oxides.
MD8.5: Advanced Fuel Designs I
Session Chairs
Chaitanya Deo
Akhil Tayal
Wednesday PM, March 30, 2016
PCC West, 100 Level, Room 106 BC
4:30 PM - *MD8.5.01
Evolution of Grain Morphology of Ceramic Nuclear Fuels under Simulated Operating Conditions
Donald Brown 1,Reeju Pokharel 1,Bjorn Clausen 1,Peter Kenesei 2,Jun-Sang Park 2,Darrin Byler 1
1 Los Alamos National Laboratory Los Alamos United States,2 Argonne National Lab Argonne United States
Show AbstractThe grain morphology, in particular the grain size and boundaries are critical to conduction of fission products (e.g. xenon) to the plenum, that is the volume around the fuel inside the cladding. Grain boundaries provide a short circuit for diffusion for fission gases to the plenum where they can increase pressure and fracture the cladding. Near-field high energy x-ray diffraction microscopy (nf-HEDM) has been used to monitor grain growth in ceramic nuclear fuel (UO2) under thermal conditions approximating those experienced in reactor. Grain mapping has been completed on samples of stoichiometric (UO2) and hyper-stoichiometric (UO2+x) nuclear fuel before and after time at temperatures in the range between 1700°C and 2000°C. The initial grain size of ceramic fuel hot pressed at 1350°C is ~5-10mm. After 3 hours at 2000°C, the grain size has grown to 30-50mm. Grain growth is accelerated in the hyper-stoichiometric ceramic.
5:00 PM - *MD8.5.02
Influence of Chemical Disorder on Energy Dissipation and Defect Evolution in Advanced Alloys
Yanwen Zhang 1,George Stocks 1,Ke Jin 1,Chenyang Lu 2,Hongbin Be 1,Brian C. Sales 1,Lumin Wang 2,Laurent Beland 1,Roger Stoller 1,German Samolyuk 1,Magdalena Caro 3,Alfredo Caro 3,William Weber 1
1 Oak Ridge National Laboratory Oak Ridge United States,2 University of Michigan Ann Arbor United States3 Los Alamos National Laboratory Los Alamos United States4 University of Tennessee Tennessee United States,1 Oak Ridge National Laboratory Oak Ridge United States
Show AbstractAlloy development is arguably one of the oldest sciences, dating back at least 3,000 years. Most efforts have been focused on alloys with one principal element and minor alloying elements. In sharp contrast to traditional alloys, recent advances of single-phase concentrated solid solution alloys (SP–CSAs) have opened up new frontiers in materials research. In these alloys, a random arrangement of multiple elemental species on a lattice (fcc or bcc) results in unique site-to-site lattice distortions and local disordered chemical environments.
We show that chemical disorder and compositional complexity in SP–CSAs have an enormous impact on defect dynamics through substantial modification of energy dissipation pathways. Based on a closely integrated computational and experimental study using a novel set of Ni-based SP-CSAs, we have explicitly demonstrated that increasing chemical disorder can lead to a substantial reduction in the electron mean free path and electrical and thermal conductivity. These reductions have a significant impact on energy dissipation and consequentially on defect evolution during ion irradiation. Considerable enhancement in radiation resistance with increasing chemical complexity is observed under ion irradiation. The insights into defect dynamics at the level of atoms and electrons provide an innovative path forward towards solving a long-standing challenge in structural materials. Understanding how material properties can be tailored by alloy complexity and their influence on defect dynamics may pave the way for new design principles of radiation–tolerant structural alloys for advanced energy systems, as well as for new defect engineering paradigms benefiting broader science and technology.
Work supported by the Energy Dissipation to Defect Evolution Center (EDDE), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.
MD8.6: Poster Session
Session Chairs
David Andersson
Gianguido Baldinozzi
Chaitanya Deo
Michael Tonks
Thursday AM, March 31, 2016
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - MD8.6.01
Determining the Effect of Temperature on the Threshold Energy of Displacement under Irradiation
Amelia Tee Qiao Ying 1,Chaitanya Deo 1,Alex Moore 1
1 Georgia Institute of Technology Atlanta United States,
Show AbstractThe threshold displacement energy is a key concept in many damage simulations and models. However it is not very well understood. The threshold displacement energy is often given as a single value while in actuality it is dependent upon crystal direction, thermal motion, impurities and more. While typically this quantity is defined at 0K, most applications involve displacement of atoms at higher temperatures. Further, in some metals and alloys, entropy stabilized phases are not stable at low temperatures and so require the threshold energy to be defined with temperature in mind. Here we develop a basic understanding of the effect of temperature on displacement of atoms in bcc metals. The threshold displacement energy of bcc-iron varies with the direction in which the primary knock-on atom (PKA) is incident on the lattice due to the interaction of the iron atoms and the geometry of the bcc lattice. The irradiation of the iron lattice was simulated using Molecular Dynamics calculations at several temperatures and the threshold displacement energies were obtained for a number of crystallographic directions. In addition, the probabilities of defect formation as a function of PKA energy were obtained for each direction and analyzed. It was found that the threshold energies were blurred largely due to atomic vibrations that are caused by increased PKA energy and thermal motion. The probability of displacement is fit to a sigmoidal function with Fermi-Dirac stastistics and the effect of temperature on the displacement of atoms is investigated.
9:00 PM - MD8.6.02
Examination of Defect Behavior in BCC Metals
Richard Hoffman 1,Chaitanya Deo 1
1 Georgia Institute of Technology Atlanta United States,
Show AbstractBCC metals are of interest for their material properties as structural materials in radiation environments, such as low defect accumulation compared to FCC metals under similar irradiation. However, constant irradiation can cause defects which affect the performance of these metals. In particular the effect of voids on the behavior of the metals has limited experimental evidence and must be examined through computational efforts. We use Kinetic Monte Carlo simulations to examine the behavior of defects in BCC metals with a particular focus on the behavior of defects over long periods of time with the addition of voids. We examine the effects that the structure of the voids and the complexity of their interaction with the other defects in the simulation have on the simulation. We demonstrate several models built using the framework provided by the SPPARKS software code developed by Sandia Labs. The first model examines the behavior of simple defects only. The second model includes the addition of voids with a constant rate of detachment. The final model examines voids with a detachment related to the binding energy as calculated from ab initio studies. Detailed sensitivity analysis of the various input parameters of the simulation is performed using the Morris’ One at a Time sensitivity method. The parameters are then compared between models and with rate equations to determine which parameters are most important for further uncertainty quantification.
9:00 PM - MD8.6.03
First Principles Study of the Structure and Elastic Properties of Thorium Metal and Thorium-Uranium Alloys
Jacob Startt 1,Chaitanya Deo 1
1 Georgia Institute of Technology Atlanta United States,
Show AbstractThorium has long been considered a possible source of fuel for use in power generating nuclear reactors. While much attention and interest have focused on the thorium oxide, metallic thorium alloys were investigated in the past as fuel candidates for fast and thermal breeder reactors. Compared to uranium, thorium metal has high melting point and negligible fission gas swelling below 800°C even after prolonged irradiation. Thorium exhibits only a single phase transition at a temperature as high as 1400°C. Stability of thorium under irradiation due to its isotropic structure may suggest the use of a thorium rich alloy, where the thorium serves as a fertile matrix for fissile Uranium. This motivates the current study of the properties of thorium and thorium uranium alloys. In this work thorium’s two solid allotropes (face centered cubic α and body centered cubic β) are modelled using Density Functional Theory (DFT) as well as the effect of increasing uranium composition on the α-phase. The Vienna Ab Initio Simulation Package (VASP) was used to create and simulate the unit cells and to determine structural and elastic properties. The density of states and electronic band structure are calculated. A conjugate gradient method was used to initially relax the unit cells and optimize lattice structures before finding the stress-strain relation and elastic behavior of the cells by providing small displacements to each atom. Using the calculated elastic constants with the Voigt-Reuss-Hill approximations, the phases’ Bulk moduli, Shear Moduli, Young’s Moduli, Poisson’s ratios, and Debye Temperatures were calculated. For the α- and β-phases four exchange-correlation potentials were used and compared in this work. The potentials used were the Linear Density Approximation (LDA), the Perdew-Burke-Ernzerhoff Generalized Gradient Approximation (PBE-GGA), a revised PBE (rPBE) and a PBE designed for solids (PBEsol). The best performing of these (the rPBE) was then chosen to repeat the process and simulate supercells of the α-thorium phase with increasing numbers of substitutional uranium atoms. All potentials showed relatively good accuracy when predicting the lattice constant. The rPBE was the most accurate, slightly over predicting by
9:00 PM - MD8.6.04
Microstructural Evolution in Hot and Cold Rolled Ti-Nb Alloys
Jacob Startt 1,Ali Tabei 2,Richard Hoffman 1,Hamid Garmestani 2,Chaitanya Deo 1
1 GWW School of Mechanical Engineering Georgia Institute of Technology Atlanta United States,2 School of Materials Science Georgia Institute of Technology Atlanta United States
Show AbstractMicrostructural analysis of interdicted U alloys may suggest processing paths leading to the establishment of the provenance of interdicted nuclear materials. Derivation of the process path functions of thermo-mechanical processing of materials provides robust computational means to analyze the microstructural evolutions. Phase transformations, morphology and crystallographic texture evolution are investigated in hot and cold rolled Ti-Nb alloys that considered as surrogates for U-Nb alloy microstructures that show the formation of metastable phases on casting and rolling. Ti-Nb is chosen because of its metastable α'' phase that is similar in nature to the αb'' metastable phase found U 6%Nb. The Ti-25.51w%Nb alloy is fabricated by arc-melting which results in extra-large grains with no stored strain energy with a β - α' microstructure. Cold rolling followed by a short homogenization leads to a β - α'' mixture with ω precipitates. Two hour annealing before cold rolling leads to a α' - α'' mixture with a characteristic triangular martensitic microstructure evidencing the act of shear on formation of the phase. Hot rolling followed by a water quench results into a β - α'' mixture, while annealing prior to hot rolling transforms the arc-melted material to a α' - α'' mixture. The crystallographic textures of similar microstructure mixtures in hot and cold rolled samples are distinctively different.
9:00 PM - MD8.6.05
Can Meta-Stable States in ab initio Calculations of Uranium Compounds be Avoided
Luis Casillas 1,Jacob Startt 2,David Andersson 3,Chaitanya Deo 2,Gianguido Baldinozzi 4
1 Univ of Tennessee Knoxville United States,2 Nuclear Radiological Engineering Georgia Institute of Technology Atlanta United States3 MST-8 Los Alamos National Laboratory Los Alamos United States4 SPMS CentraleSupelec Chatenay-Malabry France
Show AbstractDensity functional theory calculations in actinides and in particular in uranium oxides are challenging due to the correlated and localized nature of f-electrons. These systems are characterized by a complex energy landscape with local minima separated by high barriers that make their exploration complex or even impossible, depending on the initial conditioning of the calculation. Indeed, local symmetry imposes a significant constraint on electronic functions and this feature seems to be part of the problem in « high symmetry structures » like uranium dioxide. The problem was successfully addressed [1] by either the occupational matrix control, U ramping, and quasi-annealing methods. In those methods the starting point of the system is fundamental to achieve the true ground state of the system. In this paper, we would like to discuss our first hand experience how relevant are those procedures in lower symmetry structures, and give examples of systems containing different amounts of uranium, where those painstaking procedures might not be necessary
[1]Boris Dorado, Bernard Amadon, Michel Freyss, and Marjorie Bertolus,PHYS REV B,79, 235125 2009
9:00 PM - MD8.6.06
Swift Heavy Ion Irradiation Induced Modifications in Defect Fluorite Gd2Ce2O7 Containing Bixbyite Micro-Domain
Maulik Patel 1,Jeffery Aguiar 2,Kurt Sickafus 1,Gianguido Baldinozzi 3
1 Department of Material Science and Engineering Univ of Tennessee Knoxville Knoxville United States,2 National Renewable Energy Laboratory Golden United States3 CentraleSupelec, SPMS, LRC CarMEN Paris-Saclay University Paris France
Show AbstractA complex Ce bearing oxide, Gd2Ce2O7 was synthesized in order to simulate Pu in a fluorite derivative oxide. X-ray diffraction (XRD) was collected using a lab diffractometer at room temperature and Rietveld refinements of the XRD pattern was carried out using GSAS and XND programs. Diffraction analysis and complementary transmission electron microscopy analysis revealed existence of 30 nm bixbyite domains in a defect fluorite lattice. Such domains could have a profound effect on the radiation stability of this material. Thus ion irradiations were carried out using 92 MeV Xe to simulate effect of fission fragment type ions on the microstructural modifications in this material. The irradiated samples were analyzed using above mentioned experimental and analysis techniques. Preliminary analysis revealed reduction in the domain size as a function of fluence while no amorphization was observed upto the highest fluence utilized in these experiments. The diffraction data analysis and complementary data obtained from transmission electron microscopy and Raman spectroscopy analysis will be presented.
9:00 PM - MD8.6.07
Shear Melting and High Temperature Embrittlement: Theory and Application to Machining Titanium
Graeme Ackland 1,Con Healy 1,Carsten Siemers 2
1 University of Edinburgh Edinburgh United Kingdom,2 Institut fuer Werkstoffe Technische Universitaet Braunschweig Braunschweig Germany
Show AbstractWe describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding are supplanted by amorphization in a highly localized nanoscale band, which allows for massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are lack of dislocation slip systems, low thermal conduction, and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting-point elements: specifically, we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.
9:00 PM - MD8.6.08
Temperature and Electron Energy Dependent Evolution of Dislocation Loops in Yttria Stabilized Zirconia
AKM Bhuian 2,Kento Kuwahara 1,Tomokazu Yamamoto 1,Kazuhiro Yasuda 1,Syo Matsumura 1,Hidehiro YASUDA 3
1 Kyushu Univ Fukuoka Japan,2 Physical Science Division Bangladesh Atomic Energy Commission Dhaka Bangladesh,1 Kyushu Univ Fukuoka Japan3 Osaka University Osaka Japan
Show AbstractYttria stabilized cubic zirconia (YSZ) is considered to be one of the potential matrices to be used in hostile radiation environment such as nuclear reactors as well as immobilization of radioactive wastes. In the present study, we have investigated the evolution of dislocation loops in YSZ irradiated with high energy electrons as a function electron energy and irradiation temperature.
YSZ specimens were fabricated by sintering from 8 mol% Y2O3-ZrO2 powders. Microstructure evolution was monitored in situ in ultra-high voltage electron microscopes at Kyushu and Osaka University under electron irradiation with a wide range of temperatures (from 300 to 773 K), and electron energies (from 1.25 to 3.0 MeV).
The displacement energies of O and Zr sublattices in YSZ are reported to be 20~40 and 40~80 eV, respectively. Considering those values we have presumed the displacement cross-section in YSZ against required incident energy, which shows that the production rate of point defects of O and Zr sublattices strongly depends on the incident electron energy. In situ observation reveals that at 300 and 373 K with 1.25 MeV electron irradiation, no dislocation loops were formed up to 3600 sec of electron irradiation with a flux of 2.4×1023 e-/m2s. At high temperatures beyond 723 K with 3 MeV electron irradiation, perfect dislocation loops started to be nucleated from the beginning of irradiation and the size of loops gradually grew up with increasing electron fluence. On the other hand, electron irradiation at relatively lower energy and temperature (2 MeV and 300 K), the contrast of defects are different: the growth speed is lower and tiny perfect type dislocation loops are nucleated covering the whole irradiated beam. A very large loop with strong strain contrast, which is considered to be consist of solely O ions [1], are formed in this irradiation condition. Thickness of the YSZ specimen is found to be a very influential factor for the evolution of dislocation loops, and the perfect dislocation loops act as the nucleation sites of O-ion dislocation loops. The microstructure evolution of dislocation loops is discussed based on the difference in production rate of O and Zr point defects and their migration energies.
[1] K. Yasuda, C. Kinoshita, S. Matsumura, A.I. Ryazanov, J. Nucl. Mater. 319 (2003) 74.
9:00 PM - MD8.6.09
Grain Subdivision Fission Gas Swelling Model for UO2
Thomas Winter 1,Richard Hoffman 1,Chaitanya Deo 1
1 Georgia Institute of Technology Atlanta United States,
Show AbstractUnder high burnup UO2 fuel pellets can experience high burnup structure (HBS) at the rim also know as rim effect. The HBS is exceptionally porous with fine grain sizes. HBS increases the swelling further than it would have achieved at a larger grain size. A theoretical swelling model is used in conjunction with a grain subdivision simulation to calculate the swelling of UO2. The model is applied to separate regions of a fuel pellet divided based on localized temperature and fission rates. In UO2 the nucleation sites are at vacancies and the bubbles are concentrated at grain boundaries. Vacancies are created due to irradiation and gas diffusion is dependent on vacancy migration. In addition to intragranular bubbles, there are intergranular bubbles at the grain boundaries. Over time as intragranular bubbles and gas atoms accumulate on the grain boundaries, the intergranular bubbles grow and cover the grain faces. Eventually they grow into voids and interconnect along the grain boundaries, which can lead to fission gas release when the interconnection reaches the surface. This is known as the saturation point. While the swelling model used does not originally incorporate a changing grain size, the simulation allows for more accurate swelling calculations by introducing a fractional HBS based on the temperature and burnup of the pellet. The fractional HBS is introduced with a varying grain size. The pellet is then evaluated regionally to allow for the heterogeneity of the rim effect. Our simulations compare the degree of swelling along the pellet radius, especially the differences between the centerline and the rim and determine the level of swelling and saturation as a function of burnup by combining an independent model and simulation to obtain a more comprehensive model.
9:00 PM - MD8.6.10
Fretting Wear at Elevated Temperatures for APMT Reactor Fuel Cladding
Thomas Winter 1,James Huggins 2,Richard Neu 2,Preet Singh 3,Chaitanya Deo 1
1 NRE Georgia Institute of Technology Atlanta United States,2 ME Georgia Institute of Technology Atlanta United States3 MSE Georgia Institute of Technology Atlanta United States
Show AbstractIn support of a recent surge in research to develop an accident tolerant reactor, accident tolerant fuels and cladding candidates are being investigated. Relative motion between the fuel rods and fuel assembly spacer grids can lead to excessive fuel rod wear and, in some cases, to fuel rod failure. Based on industry data, grid-to-rod-fretting (GTRF) has been the number one cause of fuel failures within the U.S. pressurized water reactor (PWR) fleet, accounting for more than 70% of all PWR leaking fuel assemblies. APMT, an Fe-Cr-Al steel alloy, is being examined for the I2S-LWR project as a possible alternative to conventional fuel cladding in a nuclear reactor due to it’s favorable performance under LOCA conditions. Tests were performed to examine the reliability of the cladding candidate under simulated fretting conditions of a pressurized water reactor (PWR). The contact is simulated with a rectangular and a cylindrical specimen over a line contact area. A combination of SEM analysis and wear & work rate calculations are performed on the samples to determine their performance and wear under fretting. While APMT can perform favorably in loss of coolant accident scenarios, it also needs to perform well when compared to Zircaloy-4 with respect to fretting wear.
9:00 PM - MD8.6.11
Chemical Stability of Nanotwinned Cu Nanowires
Chun-Lung Huang 1
1 Department of Materials Science and Engineering National Tsing Hua University Hsin-chu Taiwan,
Show AbstractCu metallization with dense nanoscale twins has demonstrated excellent mechanical and electrical properties. To implement nanotwinned Cu in integrated circuits devices, failure modes of nanotwinned Cu under various driving forces have to be assessed because extreme processing and operation conditions are encountered for Cu interconnects in ultra-large-scale integrated circuits. Although the migration behavior of nanotwinned Cu subjected to thermal, mechanical and electrical stressing has been reported, the structural evolution of nanotwinned Cu under corrosive environment has not been thoroughly investigated. In this study, the chemical corrosion behavior of nanotwinned nanowires (NWs) prepared by electroplating method is reported. The results indicates that nanotwinned Cu NWs possess better corrosion resistance than conventional polycrystalline Cu NWs. The nanotwinned Cu NWs demonstrate higher rate of survival than twin-free Cu NWs after immersed in an acid solution. The surface structure of Cu NWs after corrosion is examined by high-resolution transmission electron microscopy. It is found that the presence of twin boundary may modulate the atomic-scale surface structure of Cu NWs. A tentative model is proposed to explain the effect of surface structure on corrosion characteristics of nanotwinned Cu NWs.
9:00 PM - MD8.6.12
Evaluation and Control of Mechanical Degradation of SUS310S Substrate in Superconducting Wire Processing
Seung gyu Kim 1,Najung Kim 1,Oh-min Kwon 1,Jinwoo Lee 1,Dongil Kwon 1
1 Seoul National University Seoul Korea (the Republic of),
Show AbstractSuperconductor industry wants cost of materials to be cheaper. So, the substrate made of stainless steel is considered as a substitute for Ni alloy with high cost. In 2nd generation-superconductor industry, the stainless steel is used for substrate instead of Ni alloy.
But, Yield strength and tensile stress of superconductor with stainless substrate decrease sharply after processing. The mechanical properties of superconductor is determined by substrate of it. So, we investigate variation of mechanical properties and micro structure in substrate on each processing steps.
For controlling mechanical properties of substrate, analysis of cause is done first. We evaluate microstructure of the substrates which do not pass superconductor process with nano-indentation.
And we compare the results from the substrates which have passed process.
As a result, we find that twins in the substrate after rolling go through recrystallization and recovery in high temperature process. And these make the mechanical properties decrease.
Based on the cause analysis, we propose a method capable of controlling a microstructure that is a major factor in lowering the mechanical properties of the substrate. By controlling the development of a hardened structure such as a twin in the substrate to reduce the re-crystallization degree of the substrate.
This study was carried out using a instrumented indentation for the analysis of mechanical property degradation of the superconducting wire production process using the stainless steel substrate. This work proposed a method of improving the degradation of mechanical properties by utilizing as a result, and performing a verification of the proposed scheme. We take advantage of the instrumented indentation test for doning quantitative cause analysis through the microstructure and physical property evaluation.
This research propose a new substrate manufacturing method capable of controlling the mechanical properties, reduction of the substrate is significant for having .
9:00 PM - MD8.6.13
Xe Irradiation Induced Strain in Single Crystal YSZ
Caitlin Taylor 1,Aurelien Debelle 2,William Weber 3,Maulik Patel 1
1 Materials Science and Engineering Univ of Tennessee-Knoxville Knoxville United States,2 Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse (CSNSM) Orsay France1 Materials Science and Engineering Univ of Tennessee-Knoxville Knoxville United States,3 Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge United States
Show AbstractYttria-stabilized zirconia (YSZ) is considered a potential inert-matrix fuel due to its considerable radiation damage tolerance. Xenon ions produced by fission in nuclear fuel may agglomerate to form gas bubbles, causing the matrix to swell. Ion-beam irradiation techniques were utilized to simulate Xe ion accumulation to various concentrations in single crystal YSZ. Microstructural changes due to the radiation damage, such as defect and bubble nucleation, will affect the lattice strain distribution. Xe bubbles are known to nucleate in YSZ at high enough concentrations and Xe irradiation is known to produce distinct strained layers in the YSZ matrix, but the impact of bubble nucleation, bubble number density and bubble size on lattice strain is not understood. Microstructural features due to the Xe irradiation were investigated using transmission electron microscopy (TEM) and correlated with the strain map measured using high-resolution X-ray diffraction (HRXRD). An attempt was made to understand the effect of defects on the strain profile by applying a physical model to the HRXRD patterns.
9:00 PM - MD8.6.14
Aqueous Degradation of Polyamide Membrane Materials in Halogenated Environments
Logan Kearney 1,John Howarter 1
1 School of Materials Engineering - Purdue University West Lafayette United States,
Show AbstractThe ability to measure nanoscale chemical stability of polymeric thin films is critically important for the design of new materials for applications including energy storage, membrane separations, and protective coatings where material performance is ultimately dictated by phenomena at the nanoscale. Fully crosslinked polyamide thin films were subjected to chlorinated aqueous environments, which mimicked operational conditions for polymers used in water treatment applications. Methods for in-situ measurement of the halogenation and subsequent degradation in polyamide thin films were developed using a quartz crystal microbalance. These methods were applied to rapidly evaluate chemical protection strategies that mitgated halogen adsorption and destabilzation of the polyamide netowork. As as a result of this characterization, optomized membrane materials were designed and tested in macroscale flow cell performance testing.
9:00 PM - MD8.6.15
Interpretation of Molten zncl2 Raman Spectra Using Ab Initio Methods
Abduljabar Alsayoud 1,Venkateswara Manga 1,Angharad Edwards 1,Pierre Deymier 1,Pierre Lucas 1,Krishna Muralidharan 1
1 Univ of Arizona Tucson United States,
Show AbstractThe network-forming ZnCl2-based molten salts offer potential candidate materials for high-temperature heat transfer fluids, due to their favorable combination of thermodynamic and transport properties. In spite of several experimental and theoretical investigations, the nature of tetrahedral connectivity and its temperature-dependent evolution in the network structure of pure ZnCl2 liquid are not completely understood; especially in relation to the vibrational properties of the melt. Thus here in this work, we investigate the structure and vibrational properties of the pure ZnCl2 liquid by employing ab initio molecular dynamics (AIMD) simulations in conjunction with first-principles (FP) and experimental Raman spectroscopic studies. While AIMD simulations predicted the liquid structure, a physically meaningful deconvolution of the experimental Raman spectra based on the FP calculated Raman spectra of various representative structural prototypes, revealed different modes of vibration associated with different tetrahedral connectivity in the liquid structure.
9:00 PM - MD8.6.16
A New Molecular Dynamics Method for Ionic Transport, and Its Application to Study Atomic Scale Processes of TlBr Crystals under Electric Fields
Xiaowang Zhou 1,Michael Foster 1,Patrick Doty 1,Pin Yang 2
1 Sandia National Labs Livermore United States,2 Sandia National Labs Albuquerque United States
Show AbstractIonic conduction and the related structure evolution of materials are important issues for energy storage and conversion applications. While these problems have been widely studied, fundamental scientific questions remain unanswered. As a specific example, TlBr is one of the most promising materials for g- and x- radiation detection, but its performance degrades rapidly under external electric fields. This performance degradation apparently reduces with reduction of dislocations. Improvement of materials therefore requires an understanding of various ionic conducting species and their conduction activation energy barriers, as well as the interplay between ionic conduction, dislocation, and structure evolution. Currently, the ionic conducting species are indirectly deduced from activation energy of diffusion measured in experiments and the behavior of dislocations under electric fields is even less studied. Based on a modified Stillinger-Weber potential that enables stable TlBr crystals and independent biased forces to represent external fields, we have performed molecular dynamics studies of atomic scale processes of TlBr under electric fields. Tl and Br interstitials are found to be the dominant conducting species compared to vacancies. Most interestingly, dislocations are found to move under external fields, which are supported by both our X-ray rocking curve measurement, and the experimental observation that materials with reduced dislocations have longer lifetimes. These new insights have important implications in further studies on mechanics of energy storage and conversion.
Symposium Organizers
Gianguido Baldinozzi, Paris-Saclay University
David Andersson, Los Alamos National Laboratory
Chaitanya S. Deo, Georgia Institute of Technology
Michael R. Tonks, Pennsylvania State University
MD8.7: Measuring Multiscale Effects
Session Chairs
Kurt Sickafus
Michael Tonks
Thursday AM, March 31, 2016
PCC West, 100 Level, Room 106 BC
9:15 AM - *MD8.7.01
Raman Scattering Methods for Extreme Conditions
Patrick Simon 1,Aurelien Canizares 1,Mohamed-Ramzi Ammar 1,Guillaume Guimbretiere 1,Eric Stephane Fotso Gueutue 1,Nicole Raimboux 1,Florian Duval 1,Rachelle Omnee 1,Marie-France Barthe 1,Rudy Michel 1,Jacques Poirier 1,Maggy Dutreilh-Colas 6,Thibault Labbaye 2,Eva Kovacevic 2,Chantal Boulmer-Leborgne 2,Nicolas Galy 3,Nelly Toulhoat 3,Nathalie Moncoffre 3,Ritesh Mohun 4,Lionel Desgranges 4,Magali Magnin 5,Christophe Jegou 5
1 CEMHTI CNRS Orleans Cedex 2 France,6 SPCTS Universite Limoges/CNRS Limoges France2 GREMI Université/CNRS Orleans France3 IPNL Université Lyon I / CNRS Villeurbanne France4 DEN/DEC CEA Saint Paul lez Durance France5 DEN/DTCD CEA Bagnols sur Ceze France
Show AbstractThe need for a better understanding of the behavior of materials in extreme conditions of temperature or irradiation is growing in many fields such as materials sciences, earth sciences, industrial process (refractories, glasses, ceramics), and nuclear sciences and techniques. This paper aims to review some recent experimental developments performed in CEMHTI lab. This acronym CEMHTI means “Extreme Conditions and Materials: High Temperature and Irradiation”, that shows that such conditions are the main motivation of this lab. The present paper will then review recent Raman scattering in situ developments in high temperature or/and irradiation conditions. For high temperatures, the main difficulty is thermal emission from the sample and its neighborhood, which can be filtered by time-resolved optical devices1. Moreover this also allows separation of Raman from luminescence, which constitutes a frequent difficulty precluding Raman acquisition. The potentialities of the system will be illustrated by some examples on oxide materials: phase transitions of zirconia, structural relaxation of silicas2, and reactivity of olivine ceramics.
For irradiation, a mobile Raman device, with a fiber-coupled probehead, was developed to monitor materials behavior under light ions beam (He2+, H+) supplied by a cyclotron. This system equiped with different sample chambers allows to investigate various conditions of irradiation: irradiation damages in solid actinide oxides (Th, U) 3,4, radiolysis of solid/water interfaces (UO2/H2O)5, radiolytic corrosion of nuclear graphites (in a device combining high temperature, high pressure, and irradiation conditions). For uranium the understanding acquired in these experiments allows in a following step to consider more active materials4 such as PuO2 and even spent nuclear fuels6.
This mobile device can be in fact used in much more situations than the only nuclear field. It only needs an optical access to the phenomenon to investigate, and a probehead adapted to the optical focus distance. As an example, Raman monitoring of carbon nanotubes growth in a PECVD reactor will be presented7.
(1) P. Simon et al., Journal of Raman Spectroscopy 2003; 34, 497.
(2) M. Dutreilh-Colas et al., J. Am. Ceram. Soc. 2011; 94, 2087.
(3) G. Guimbretiere et al., Applied Physics Letters 2013; 103, 041904.
(4) R. Mohun et al., Nuclear Instruments and Methods in Physics Research Section B 2015.
(5) A. Canizares et al., Journal of Raman Spectroscopy 2012; 43, 1492.
(6) C. Jegou et al., J. Nucl. Mater. 2015; 458, 343.
(7) T. Labbaye et al., Applied Physics Letters 2014; 105, 213109.
9:45 AM - MD8.7.02
Simulation and Measurement of Thermal Conductivity in UO2 and MOX
Michael Cooper 1,Xiang-Yang Liu 1,David Andersson 1,Christopher Stanek 1
1 Los Alamos National Laboratory Los Alamos United States,
Show AbstractTo fully utilize nuclear fuel its material properties must be maintained under extreme conditions. Thermal conductivity is particularly important owing to its role in mitigating centerline fuel melting. Firstly, the role of UO2 magnetism in phonon scattering has been investigated experimentally. Furthermore, through the Callaway Model magnetism sufficiently accounts for the difference between molecular dynamics and experiment at low temperatures. By combining defect-phonon scattering (from molecular dynamics) with the magnetic contribution (from experiment), the Callaway Model can be parameterized to predict the degradation of UO2 thermal conductivity due to different fission products. Zr, Xe, La and Pu are all predicted to influence thermal conductivity to different degrees depending on their valance state and atomic size relative to the host lattice. Furthermore, the model is extended to include magnetic scattering for predictions of thermal conductivity of mixed oxides, UPuO2 and UThO2.
10:00 AM - MD8.7.03
Glancing-Incidence X-Ray Techniques for Film Analysis
Gianguido Baldinozzi 2,Philippe Lecoeur 3,Abhishek Bose 2,Chenyi Li 2,Thomas Maroutian 3,Vassilis Pontikis 2,Laurence Luneville 1,David Simeone 1
1 SPMS, LRC Carmen Centralesupelec, CNRS Châtenay-Malabry France,2 DMN, SRMA, LRC Carmen CEA Gif-sur-Yvette France,3 Institut d’Electronique Fondamentale Université Paris-Sud Orsay France4 DSM, IRAMIS, LSI CEA Gif-sur-Yvette France,2 DMN, SRMA, LRC Carmen CEA Gif-sur-Yvette France5 DM2S, SERMA, LRC Carmen CEA Gif-sur-Yvette France,1 SPMS, LRC Carmen Centralesupelec, CNRS Châtenay-Malabry France2 DMN, SRMA, LRC Carmen CEA Gif-sur-Yvette France,1 SPMS, LRC Carmen Centralesupelec, CNRS Châtenay-Malabry France
Show AbstractApplications of glancing-incidence X-rays, to be specific the glancing-incidence diffraction for characterization of textured films and depth profiling of residual stresses are described. In a glancing-incidence experiment, the detector is in a horizontal plane parallel to the film surface to measure diffraction from lattice planes which make an angle to the surface. Especially for the analysis of thin films, x-ray diffraction techniques have been developed for which the primary beam enters the sample at very small angles of incidence. In its simplest variant, this configuration is called GIXRD: glancing incidence x-ray diffraction. The small entrance angle causes the path traveled by the impinging X-rays to increase significantly and the structural information contained in the diffraction pattern to come forth primarily from the thin film. The parafocusing geometry, as applied in conventional powder diffractometry, cannot be used in those experiments and devices for parallel x-ray optics need to be used (e.g. laterally graded multilayer mirrors).
In a stress/strain depth profiling experiment, values of strains and residual stresses averaged over different penetration depths beneath the film surface (or z-profiles) are obtained by asymmetric diffraction from crystal planes which are inclined to the film surface. The actual strain at different depths under the surface (z-profiles) is extracted from the average values using inverse Laplace and numerical inversion methods. The measurement of depth-dependent properties may be also generalized to the concentration of a chemical phase, the amorphous fraction, the crystallite size, microstrain or macrostrain or any other. On the basis of simple considerations one may define an attenuation length that allows expressing that depth-averaged property derived from a Bragg reflection and the the task of obtaining the local value of that interesting property function can be restated as a problem of inverse Laplace transformation.
Examples of such analyses of graded strain in sputtered W films are given. This work is partly supported by a grant of Investissements d’Avenir of LabEx PALM (ANR-10-LABX-0039-PALM).
10:15 AM - MD8.7.04
Thermal Effects in 3 Phase Composites Containing MgAl2O4 + YSZ + Al2O3: An In Situ High Temperature XRD Study
Maulik Patel 1,Kevin Mathew 2,Kenta Ohtaki 3,Martha Mecartney 3,Kurt Sickafus 1
1 Department of Materials Science and Engineering University of Tennessee Knoxville United States,2 Department of Mechanical, Aerospace, and Biomedical Engineering University of Tennessee Knoxville United States3 Department of Material Science and Engineering University of California Irvine United States
Show AbstractA Ceramic-Ceramic composite fuel model has been proposed by several researchers as an alternative advanced nuclear fuel with the goal of increasing the thermal conductivity and reducing microstructure evolution due to defect accumulation. Understanding the structural modifications of ceramic composites with different grain sizes at elevated temperatures is therefore of fundamental importance. In this study, dynamical thermal effects were evaluated in model three phase composites of different grain sizes consisting of equal amounts of YSZ, MgAl2O4 and Al2O3 using in-situ high temperature x-ray diffraction (HTXRD) from room temperature to 1100°C. Crystallite size, strain and unit cell volume changes were determined as a function of temperature. Thermal expansion coefficients for each of these phases in a composite were also deduced and compared with those obtained for single phases.
MD8.8: Metallic Systems II
Session Chairs
Gianguido Baldinozzi
Par Olsson
Thursday PM, March 31, 2016
PCC West, 100 Level, Room 106 BC
11:15 AM - MD8.8.02
Identification of ‘Effective Grain’ Boundary for Cleavage Fracture Resistance Considering Crystallography of Variants in Low-Carbon Lath Martensitic Steel
Arya Chatterjee 1,Abhijit Ghosh 1,Rahul Mitra 1,Debalay Chakrabarti 1
1 Indian Inst of Tech-Kharagpur Kharagpur India,
Show AbstractMechanism of cleavage crack propagation during testing of standard Charpy V-notch specimen at -196°C has been investigated in a low-carbon lath martensitic steel (modified 9Cr-1Mo steel) using electron back-scattered diffraction (EBSD) technique. The microstructural units of martensitic structure are characterized in terms of Kurdjumov-Sachs (K-S) crystallographic variants and subsequently the boundaries present in the martensitic structure (sub-block, block and packet boundaries) are identified to understand thoroughly the structure-property correlation of this steel. EBSD study of cleavage crack path indicated that block boundaries are more effective in cleavage crack retardation as compared to packet boundaries, whilst sub-block boundaries are ineffective in crack resistance. Moreover, characterizing boundaries in terms of misorientation (angle-axis) angle may be misleading to identify the role of boundary in cleavage crack resistance.
11:30 AM - MD8.8.03
Oxidation Resistant Tungsten Carbide Cermets
Samuel Humphry-Baker 1,William Lee 1,Ke Peng 2
1 Imperial College London London United Kingdom,1 Imperial College London London United Kingdom,2 State Key Laboratory for Powder Metallurgy Central South University Changsha China
Show AbstractTungsten carbide cermets are strong candidate materials for neutron shields in fusion reactors, due to their short mean-free-path for high-energy neutrons (Windsor et al, Nucl. Fusion 2015), excellent thermo-mechanical properties and manufacturability. However, they are susceptible to high temperature oxidation, which is problematic for reactor accident scenarios. For instance with a sudden air-ingress at high temperature, tungsten oxides can volatilise and release dangerous transmutation products. We have developed a successful process for depositing compositionally graded coatings with improved oxidation resistance. The coating formation mechanism could be of wide interest to the field of graded materials production, which is usually categorised into two main classes of processes (Suresh Int. Mat. Rev 1995): (i) constructive, i.e. coating or stacking of constituents in sequence; and (ii) transport-based, where diffusional phenomena create the compositional gradients. The coating process we present combines both constructive and transport processes simultaneously, resulting in the separation of key oxidation-resistant constituents to the surface. Crucially, this segregation process is fundamental to the superior oxidation performance, which outperform conventional coatings (e.g. boriding) by 2 or more orders of magnitude. We firstly compare the baseline oxidation studies of coated and pristine cermets by combining thermogravimetric analysis (between 600 and 1000 o C) with electron microscopy and X-ray diffraction, then reveal the mechanism of surface passivation, and finally demonstrate the coatings’ tomographic structure and formation mechanism.
11:45 AM - MD8.8.04
Understanding the Role of Hydrogen on the Slip Transmission Behavior in α-Fe: Implications on Intergranular Failure
Ilaksh Adlakha 1,Kiran Solanki 1
1 Arizona State University Tempe United States,
Show AbstractThe mechanical properties of polycrystalline materials are strongly governed by the presence of obstacles to dislocation motion. The grain boundaries (GBs) present an effective barrier to the dislocation motion, thereby strengthening the material. However, the presence of an aggressive environment such as hydrogen increases the susceptibility to intergranular fracture. There is a strong need to systematically investigate the role of corrosive environment on the dislocation-grain-boundary interactions from the perspective of failure mechanisms. In this work, we employ molecular dynamics to study the interactions between screw dislocations and several <111> tilt GBs in Fe. It was found that outcome of the dislocation-GB interaction depends strongly on the underlying GB structure. Further, there existed a strong correlation between the GB energy and the energy barrier for dislocation transmission. In other words, GBs with lower interfacial energy demonstrated a higher barrier for slip transmission, which are in agreement with previous experimental and modeling efforts. The introduction of hydrogen along the grain boundary causes the energy barrier for slip transmission to increase consistently for all of the grain boundaries examined. The energy balance for a crack initiation in the presence of hydrogen was examined with the help of our observations and previous findings. It was found that the presence of hydrogen increases the strain energy stored within the grain boundary which could lead to a transgranular-to-intergranular fracture mode transition.
12:00 PM - MD8.8.05
Multiscale Modeling of Intergranular Fracture Due to Diffusion-Assisted Hydrogen Embrittlement
Benyamin Gholami Bazehhour 1,Ilaksh Adlakha 1,Jay J. Oswald 1,Kiran Solanki 1
1 Arizona State University Tempe United States,
Show AbstractA sequential multiscale model for finite element analysis of intergranular fracture process in metallic microstructures coupled with hydrogen embrittlement is presented. The two dimensional polycrystalline structure ahead of the notch in the specimen is represented implicitly and solved by a non-linear extended finite element method (XFEM) solver. In order to take into account the effect of concurrent stress-assisted hydrogen embrittlement of grain boundaries, a convection-diffusion equation is numerically solved on the network of grain boundaries to estimate the grain boundary degradation of cohesive strength. For that purpose, hydrostatic stress along the grain boundaries is introduced into the formulation of hydrogen transport. Grain boundary properties are quantified by atomistic simulations and employed in the XFEM framework using a modified cohesive zone model to bridge the different length scale calculations. Also a rate-dependent crystal plasticity model is incorporated into XFEM to account for orientation dependent elasto-plastic deformation. Effect of hydrogen coverage and microstructural properties, such as grain boundary character on the crack initiation and growth is studied.
12:15 PM - MD8.8.06
Accurate Description of Phase Transition in Sn in Terapascal Pressure Range with Quantum Monte Carlo
Roman Nazarov 1,Randolph Hood 1,Miguel Morales 1
1 Lawrence Livermore National Lab Livermore United States,
Show AbstractThe accurate prediction of phase transitions is one of the most important research areas in modern materials science as it often replace otherwise difficult or even impossible to get experimentally measured properties of selected phases. Density functional theory (DFT) was for a long time the main workhorse for such calculations. As a simple mean field method DFT employs different forms of approximate exchange-correlation functionals which often fails to describe accurately several phenomena as bonding, cohesion, conductivity, optical properties and other quantum effects. As a result one can encounter overstabilization of one phase compared to another, especially if two phases belong to different classes (e.g. metal and semiconductor). A recent example of such deficiency has been demonstrated in Sn: no bcc to hcp phase transition has been observed in Sn when dynamically compressed to 1.2 TPa while DFT predicts a transition to occur at 0.16-0.2 TPa [1].
To overcome the limitations of DFT, we have employed modern Quantum Monte Carlo (QMC) methods which treat the many body electron problem directly and allow us to systematically improve the results. Despite being more computationally demanding that a standard DFT, the accuracy that QMC provides can justify additional expenses.
We have applied one QMC flavor, diffusion quantum Monte Carlo (DMC), to study the pressure induced phase transitions in Sn. In order to get highly accurate results we systematically assess the effect of controllable approximations of DMC such as fixed node approximation, finite-size effects and the use of pseudopotentials. We then compare the reliable equations of state for several Sn phases with DFT all-electron and pseudopotential calculations to evaluate the accuracy of exchange-correlation functionals and the choice of effective core potential. Based on metrologically accurate equation of states we construct the pressure-temperature phase diagram and confirm dramatic effect of energetic phase stability on it. Based on our careful analysis we demonstrate that modern DMC calculations have a superior accuracy compared to DFT and allow accurate description of phase transitions.
[1] A. Lazicki et al., X-Ray Diffraction of Solid Tin to 1.2 TPa. Phys. Rev. Lett. 115, 075502 (2015)
12:30 PM - MD8.8.07
Discrete Dislocation Plasticity Modelling of High-Temperature Alloys Incorporating Diffusion along Particle/Matrix Interfaces
Siamak SoleymaniShishvan 1,Vikram Deshpande 1
1 University of Cambridge Cambridge United Kingdom,
Show AbstractWe model the diffusional high temperature deformation of particulate composites using a discrete dislocation modelling framework. Interfacial diffusional deformation between the particles and the matrix is modelled by a stress-driven diffusion model while plastic deformation of the matrix involves both the glide of dislocations and their climb due to vacancy diffusion. The results demonstrate that while dislocation climb within the matrix reduces the strength of the composite, it results in the formation of dislocation cell structures within the matrix. These cell structures in turn bring additional length scales into the deformation process which results in a size dependence of the strength of composites. Moreover, the formation of cell structures is facilitated when the climb of dislocations coupled with the deformation of the particle/matrix interfaces due to diffusion. Parametric studies on the effect of the interfacial diffusion rates and the climb rates of the dislocation are presented to highlight the relative role of these parameters in the coupled deformation of the composites at high temperatures.
12:45 PM - MD8.8.08
Signatures of Shock-Induced Phase Transitions in Local Structure Measurements
Akhil Tayal 1,Steven Conradson 1,Saryu Fensin 2,Ellen Cerreta 2
1 Soleil Saint-Aubin - BP48 France,2 Materials Science and Technology Division Los Alamos National Laboratory Los Alamos United States
Show AbstractShock produces pressures much more extreme than attainable under equilibrium conditions, albeit transiently, anisotropically, and in a combination of alternating compression and rarefaction waves. Shock can therefore induce transitions to high pressure and other phases, at pressures that may vary considerably from those under hydrostatic conditions. The formation of these phases is not necessarily fully reversible, leaving altered material as a signature. These provide the information from which the the atomic scale shock mechanism can be reconstructed. The standard methods of characterizing post-shock material include crystallography and transmission electron microscopy (TEM). Crystallography, however, is limited in that it only gives information on the average atomic positions of the periodic component of a material, being insensitive to aperiodic local lattice distortions and amorphous regions that exhibit short range order. TEM also depends to a lesser extent on long range order, and requires samples that are thin along the beam direction and so susceptible to elastic relaxation that may eliminate altered structures trapped by stress. Local structure methods, pair distribution function analysis and X-ray Absorption Fine Structure (XAFS) spectroscopy, that penetrate the material are therefore a useful and perhaps necessary complement to these more conventional techniques. This is demonstrated by XAFS studies of shocked Zr and Cu(Pb), in both of which the local structure gives different results than the diffraction. A common response of cubic materials to shock is the formation of hexagonal, omega phases in which the symmetry is lowered by changes in the lattice parameter along the unique direction, which is presumably the same as the shock propagation through the material. An issue, however, is whether this modified interplanar spacing is uniform throughout the material or varies between locations. Unless the domains are relatively large, diffraction will give the average spacing without necessarily indicating the amount of disorder, especially if some of the domains are below the diffraction limit in size. In the case of shocked Zr, we do find such a difference in the remnant omega phase, demonstrating that its domains are irregular with a substantial fraction being relatively small. Shocked Cu(Pb) was probed with a 2 micron beam that allowed the interiors of the grains to be mapped by XAFS. No difference was found as a function of position relative to the grain boundaries, but all of the probed spots showed the presence of an shell extraneous to the oriignal fcc structure that we interpet as an hcp distortion. That it is invisible in bulk diffraction measurements demonstrates that these domains are only nanometers in size and also that the distortion is disordered, possibly by being randomly oriented. These novel results therefore indicate that the forward and reverse transitions are more complex than previously believed.
MD8.9: Metallic Systems III
Session Chairs
David Andersson
Vassilis Pontikis
Mitra Taheri
Thursday PM, March 31, 2016
PCC West, 100 Level, Room 106 BC
2:30 PM - *MD8.9.01
First Principles Based Study of Displacement Damage in bcc Metals
Par Olsson 1,Christophe Domain 2,Charlotte Becquart 3
1 KTH Royal Institute of Technology Stockholm Sweden,2 MMC EDF Ramp;D Moret sur Loing France3 Universite Lille-1 Villeneuve d'Ascq France
Show AbstractDisplacement damage due to irradiation-matter interaction is the primordial reason for material degradation in radiation fields. The knowledge of the energy limits to generate damage has historically been generated using semi-empirical interaction potential in all but a few select materials, most notably in semi-conductors or insulators, where first principles molecular dynamics has been applied. Here, we will show recent developments in studying displacement damage, and the threshold energies, using first principles electronic structure theory in bcc metals, focusing on Fe and W for their importance in current and next generation nuclear energy applications. Even applying first principles methods, it is shown how important the choice of approximations are. The difference between the refractory W and softer Fe is highlighted and discussed. How to generate more reliable interatomic potentials for the critical short range interaction, between the screened Coulomb limit and the thermodynamic range of validity is treated explicitly. Optimization techniques to speed up these extremely costly calculations are also decribed. First results on the sensitivity to minor alloying elements will be discussed.
3:00 PM - MD8.9.02
Mechanical Property Evolution of Ion-irradiated Candidate Structural Alloys for Gen-IV Nuclear Reactors Utilizing Small-scale Mechanical Testing
Anya Prasitthipayong 1,David Frazer 2,Manuel-David Abad 2,Scott Tumey 3,Andrew Minor 4,Peter Hosemann 2
1 Department of Materials Science and Engineering University of California, Berkeley Berkeley United States,2 Department of Nuclear Engineering University of California, Berkeley Berkeley United States3 Center of Accelerator Mass Spectrometry Lawrence Livermore National Laboratory Livermore United States1 Department of Materials Science and Engineering University of California, Berkeley Berkeley United States,4 National Center for Electron Microscopy Lawrence Berkeley National Laboratory Berkeley United States
Show AbstractCompelling demands to reduce carbon dioxide emissions worldwide have created significant pressure to shift from extensive reliance on carbon-based energy sources to more carbon-neutral alternatives such as nuclear energy. Gen-IV is the next generation of nuclear reactor designs that requires structural materials to tolerate hostile environments that lead to undesirable microstructural evolution and deterioration in mechanical performance such as severe hardening and embrittlement. This necessitates the development of novel advanced structural materials that will be able to withstand higher operating temperatures, higher irradiation doses and extremely corrosive environments. Potential materials include ferritic-martensitic steels, austenitic stainless steels and oxide dispersion strengthened (ODS) steels.
Ion irradiation is often used in lieu of neutron irradiation for nuclear-reactor-based research. Studying the influence of neutron irradiation on nuclear reactor materials can often be costly and extremely difficult. Neutron-irradiated materials become radioactive in reactor-irradiation environments and require long irradiation exposure times to simulate real world use. Ion irradiation on the other hand requires significantly less time to achieve the same dose. However, the low penetration depth of ions restricts the amount of irradiated material for study, necessitating the development of small-scale mechanical testing techniques for ion-irradiated materials.
Our presentation will focus on small-scale mechanical testing of selected ion-irradiated candidate structural alloys for Gen-IV reactors, including: 800H, T91, nano-crystalline T91 (NCT91) and 14YWT. Fine-grained 14YWT is an exceptionally good representative of the ODS class of alloys due to its unique microstructure and nano-structured characteristics. 14YWT has not only high radiation resistance, owing partly to yttrium-rich nanoparticles that act as irradiation-induced defect sinks, but also desirable mechanical properties and stability at high temperatures.
The aforementioned candidate alloys were irradiated with 70 MeV Fe9+ bombarding ions, at 443°C to a dose of 20.680 dpa. The damage layer (ion penetration depth) is approximately 6.2 μm into the samples. Nanoindentation and in situ micro-compression testing were chosen to evaluate mechanical responses to ion-irradiation. Our initial results show that significant increases in hardness and yield stress observed in our ion-irradiated alloys are similar to neutron-irradiated alloys.
3:15 PM - MD8.9.03
Role of Local Crystallographic Texture on Splitting in Low Carbon Steel
Abhijit Ghosh 1,Sudipta Patra 1,Arya Chatterjee 1,Debalay Chakrabarti 1
1 Metallurgical and Materials Engineering Indian Institute of Technology Kharagpur Kharagpur India,
Show AbstractDuring the Charpy impact testing of controlled rolled high strength low alloy steel, a special type of crack is often found on the fracture surface, which propagates through the transverse plane with respect to the main fracture plane. This type of crack on the fracture surface is commonly known as splitting or fissure or delamination. The role of crystallographic texture on splitting is studied through combined scanning electron microscopy and electron backscattered diffraction analyses on the sample, finish rolled at different temperatures (820°C - 650°C). Through thickness texture band composed of cube (ND parallel to <001>) and gamma (ND parallel to <111>) fibre orientations has been found to be developed during the intercritical-rolling treatment. Splitting crack is found to propagate between these two texture bands on the main fracture plane owing to strain incompatibility. In order to understand the crack deflection at grain boundary, different combination of neighboring crystal orientations has been considered and possible tilt and twist angle has been evaluated. A new approach based on the angle between {001} planes of neighbouring crystals has been employed in order to estimate the ‘effective grain size’, which is used to determine the cleavage fracture stress on different planes of the sample. The severity of splitting is found to be directly related to the difference in cleavage fracture stresses between the ‘main fracture plane and ‘splitting plane’. Finally, a phenomenological model has been developed to represent the mechanism of splitting.
3:30 PM - MD8.9.04
Corrosion of Single-Phase Magnesium Aluminum Alloys
Ashlee Wingersky 1,Anna Weiss 1,Karl Sieradzki 1
1 Arizona State University Tempe United States,
Show AbstractOwing to their lightweight, magnesium-based alloys such as AZ91D and AM60B are currently being incorporated into automotive designs. One of the major concerns in using these materials is their susceptibility to corrosion-induced damage. The corrosion behavior of cast Mg-Al alloys is dependent on the alloy composition and microstructure. Our research is aimed at understanding the compositional changes occurring on the surface of these alloys when exposed to aqueous environments, since these changes govern their long-term corrosion behavior.
We present experimental data for the corrosion behavior of a model system composed of elemental Mg with 5 at% aluminum in solid solution. Accelerated corrosion testing of this alloy shows the evolution of 100-micron size aluminum rich platelets that cover about 30% of the alloy surface. We investigate the mechanism for platelet evolution using Kinetic Monte Carlo simulations. These results show that this morphology evolves by a dealloying process involving the selective dissolution of Mg, which occurs via a layer-by-layer process involving step flow. The implications of our results for the corrosion behavior of the more complicated commercial alloys are discussed.
3:45 PM - MD8.9.05
High Temperature Oxidation Behavior of APM and APMT under Dry Air/Steam Condition
KkochNim Oh 1,KwangSup Eom 1,Zhiyuan Liang 1,Preet Singh 1
1 Georgia Institute of Technology Atlanta United States,
Show AbstractLight water reactors, which represent the vast majority of nuclear reactors in the world, use Zr-based alloys as fuel cladding material, due to their very low cross-section for thermal neutron absorption coupled with good mechanical properties and corrosion resistance at normal operating conditions. However, upon significant temperature increase, such as the one that occurred during the Fukushima Daiichi accident, these alloys experience significant decrease in strength and tend to burst at temperatures between 700 °C and 1100 °C, depending on the rod’s internal pressure. Most importantly, the exothermic Zr oxidation becomes self-catalytic at temperature above 1200 °C, resulting in significant hydrogen production and consequent explosion hazard. Because of this, efforts are ongoing worldwide to develop the so-called Accident Tolerant Fuels, i.e. fuel/cladding materials capable to survive loss of cooling for a longer period of time compared to Zr-based alloys.
One approach is to use advanced ferritic stainless steels as cladding materials, since they have the potential to overcome some of the limitation of Zr-based alloys. High temperature oxidation resistance and high temperature strength properties can be easily modified by controlling various alloying elements in ferritic steels in order to satisfy their application performance objectives. Considering the stress corrosion cracking (SCC), an important corrosion phenomenon in nuclear power plants, ferritic stainless steels have an excellent resistance compared to that of austenitic stainless steels, therefore the former is more suitable for the cladding materials in order to prevent the unpredictable failure in advance. Specifically, this study focuses on alumina-forming ferritic stainless steels since they were shown to have an excellent oxidation resistance at high temperature compared to Zr alloys. But, there is a limited amount of data on high temperature oxidation of these advanced ferritic stainless steels, it is necessary to establish data on high temperature oxidation behavior for these alloys under severe conditions.
With respect to high temperature oxidation of APM and APMT under dry air condition, weight gains at temperatures from 600 °C to 900 °C were similar or better to that for ZIRLO® at 400 °C. The dense oxide layers, with no cracks, formed on the APM and APMT alloy surfaces at 1100 °C, which composed of ~66 at.% of O and ~33 at.% of Al and its thickness was ~3 µm. In particular, APMT showed lower rate constant over the whole temperature range between 600 °C and 1100 °C and had a lower activation energy than APM.
For high temperature oxidation behavior of APM and APMT under 100% steam condition, oxidation rate was higher compared to the equivalent tests done under dry air condition. Moreover, the grain size and the thickness of oxide layer of APM and APMT under 100% steam condition were larger and thicker than those under dry air condition.
MD8.10: Modeling Nanocrystals and Interfaces
Session Chairs
KkochNim Oh
Michael Tonks
Ting Zhu
Thursday PM, March 31, 2016
PCC West, 100 Level, Room 106 BC
4:30 PM - *MD8.10.01
Probing the “Immunity” of Grain Boundaries under in situ Irradiation in Nanocrystalline Metals
Osman El-Atwani 1,Asher Leff 1,Khalid Hattar 2,Mitra Taheri 1
1 Drexel Univ Philadelphia United States,2 Sandia National Laboratories Albuquerque United States
Show AbstractNanocrystalline metals are comprised of a high density of grain boundaries, which act as sinks for radiation induced defects. Defect denuded zones should be more dominant in a nanocrystalline material, and this concept could lead to improved radiation tolerance. Advancement in the understanding of radiation damage has shown, however, that the concept of a constant or stable denuded zone does not seem to hold true. The efficiency of the grain boundaries as defect sinks play a significant role in the ability of a nanocrystalline metal to reduce radiation damage. To probe the relationship between denuded zone development, grain boundary efficiency, and dislocation behavior, precession electron diffraction was coupled with in situ irradiation to determine any connection between denuded zones and local dislocation densities. In-situ irradiation was performed in a transmission electron microscope (TEM) on freestanding nanocrystalline Fe samples using the i3TEM facility in the Department of Radiation Solid Interactions at Sandia National Laboratories. Automated crystallographic orientation mapping (ACOM) was also performed via NanoMEGAS ASTAR precession diffraction; dislocation densities were calculated from orientation data using the Nye tensor. Irradiations were performed with 10 keV Helium (He) ions at 300°C, and specific regions were monitored and analyzed throughout irradiation. Grains that appeared to have denuded zones at low dpa started to collapse at intermediate dpa ranges. At high dpa, many denuded zones were completely vanished. Grain boundary analysis using the Nye tensor method demonstrated high an increase in defect densities near the boundary with increasing dose, correlating with denuded zone collapse. The breakdown of denuded zones corresponded with an increase in geometrically necessary dislocations at the boundary, indicating that the boundary defect structure had been changed by the absorption of radiation defects.
5:00 PM - MD8.10.02
Atomistic Study of Hetero-Phase, Semi-Coherent Interfaces between Immiscible Metals: The Cases of AgCu and CuW
Vassilis Pontikis 3,Gianguido Baldinozzi 3,Abhishek Bose 3,Chenyi Li 3,Laurence Luneville 2,David Simeone 2
1 DSM, IRAMIS, LSI CEA Gif-sur-Yvette France,3 DMN, SRMA, LRC Carmen CEA Gif-sur-Yvette France,2 SPMS, LRC Carmen Centralesupélec, CNRS Châtenay-Malabry France,3 DMN, SRMA, LRC Carmen CEA Gif-sur-Yvette France4 DM2S, SERMA, LRC Carmen CEA Gif-sur-Yvette France,2 SPMS, LRC Carmen Centralesupélec, CNRS Châtenay-Malabry France3 DMN, SRMA, LRC Carmen CEA Gif-sur-Yvette France,2 SPMS, LRC Carmen Centralesupélec, CNRS Châtenay-Malabry France
Show AbstractWe investigate semi-coherent interfaces between immiscible metals, AgCu and CuW, by means of Molecular Dynamics and Monte Carlo atomistic simulations relying on phenomenological n-body potentials taken from the literature or developed on purpose. The last are shown to comply with the experimental phase diagrams of the binary systems, namely by reproducing the large miscibility gap existing between their constituents. Furthermore, it is shown that at the thermodynamic equilibrium, unlike bulk systems, a smooth miscibility profile exists across hetero-phase interfaces, necessary for minimizing the excess free energy of the interface. These findings suggest that welds between not miscible metals are possible. Ongoing work focuses on the mechanical stability and resistance of such assembles.
We acknowledge partial support through grant ANR-10-LABX-0039-PALM of “Investissements d’Avenir of LabEx PALM”.
5:15 PM - MD8.10.03
Lattice Dynamics of Core-Shell Bimetallic Nanocrystals during Ultrafast Laser Excitation
Kiran Sasikumar 1,Mathew Cherukara 1,Jesse Clark 2,Thomas Peterka 1,Ross Harder 1,Subramanian Sankaranarayanan 1
1 Argonne National Laboratory Lemont United States,2 University College London London United Kingdom
Show AbstractEnergy transport via lattice vibrations (phonons) play a crucial role in several applications such as heat dissipation in semiconductors, waste heat energy conversion via thermoelectric materials, and phase transitions and cavitation phenomena in intensely heated nanofluids. Investigation of the temporal behavior of externally stimulated materials, under severe thermal non-equilibrium conditions, can lead to crucial insights for energy research.
Recently, experimental techniques have evolved to conduct time-dependent lattice dynamics measurements in nanomaterials. In particular, Bragg Coherent Diffraction Imaging (BCDI) in conjunction with optical pump-probe experiments via ultrafast x-ray lasers has been used to directly image the generation and subsequent evolution of coherent acoustic phonons within nanocrystals. In particular, experiments on bimetal (Au/Al) core-shell nanocrystals have revealed inhomogeneous effects in the lattice breathing upon heating with femtosecond x-ray lasers. Conventional theoretical models cannot be used to explain the physics of the phenomena in such non-equilibrium environments that involve extreme heat fluxes and temperature gradients.
Atomistic molecular dynamics (MD) simulation is an appropriate technique to investigate lattice dynamics in such environments, particularly in core-shell structures where interfacial effects can play an important role in phonon scattering. With the convergence of time and length scales accessible by both experiments and simulations, we are now able to integrate experimental observations with multi-million atom MD simulations to enhance the fundamental understanding of materials behavior under extreme environments.
In this talk, we focus on the MD simulations performed on core-shell bimetallic nanocrystals under the influence of extreme heat fluxes. We explore the vibrational modes that dominate lattice breathing and look into the effect the nanoparticle size and shape have on the same. In addition, we attempt to identify the origin of the inhomogeneous effects, observed experimentally, in the lattice breathing of core-shell structures. Finally we investigate the effects of lattice mismatch between the core and shell material, the shell-to-core size ratio and the interfacial structure to tune the lattice dynamics of core-shell nanocrystals.
5:30 PM - MD8.10.04
Dynamic Mechanical Behavior Stability of a Nanocrystalline Cu-Ta Alloy
Scott Turnage 1,Mansa Rajagopalan 1,Kristopher Darling 2,Mark Tschopp 2,Kiran Solanki 1
1 Arizona State University Tempe United States,2 Army Research Laboratory Aberdeen Proving Grounds United States
Show AbstractAt high strain rates (103 – 104 s-1), metals experience a dramatic increase in flow stress as a result of phonon drag. This increase in flow stress accompanies a decrease in ductility which is undesirable for high energy impact materials such as shaped charge liners and ballistic penetrators. An effective means of limiting the effect of phonon drag is to keep the speed of dislocation propagation below a critical maximum. This can be achieved through the introduction of obstacles such as grain boundaries. Nanocrystalline materials show great potential for high energy impact materials due to the high number of grain boundaries which keep the mechanical response stable with respect to strain rate, but maintaining a nanocrystalline microstructure is a challenge under dynamic loading scenarios. Recently, a nanocrystalline Cu 10 at.% Ta alloy has been shown to maintain a refined microstructure under high temperature and dynamic loading conditions. Here, we further investigate the alloy through high strain rate testing on a split Hopkinson pressure bar to determine the stability of the mechanical properties with respect to strain rate. The microstructure is analyzed before and after deformation using high resolution transmission electron microscopy along with precession diffraction. Results show that the stable nanocrystalline microstructure correlates to stable flow stress behavior at strain rates up to 104 s-1. Further, twinning is observed after deformation indicating that the deformation mechanism of the nanocrystalline Cu-Ta alloy is largely affected by twin formation and its interactions at high strain rates leading to lower sensitivity of the flow stress to the strain rate.
5:45 PM - MD8.10.05
Microstructural Evolution of a Nanocrystalline Copper-Tantalum Alloy
Mansa Rajagopalan 1,Scott Turnage 1,Kristopher Darling 2,Mark Tschopp 2,Kiran Solanki 1
1 School for Engineering of Matter, Transport, and Energy Arizona State University Tempe United States,2 Weapons and Materials Research Directorate Army Research Laboratory Aberdeen proving Ground United States
Show AbstractUnderstanding the behavior of materials through systematic evaluation of microstructure with deformation at the macro and nano scale is critical for designing materials for engineering applications under extreme conditions. In this present study, microstructural evolution of a binary nanocrystalline copper - 10 at. % tantalum alloy prepared through mechanical alloying and consolidated through the equal channel angular extrusion (ECAE) process was investigated using high strain rate experiments (103/s to 104/s) at high temperatures (25 to 600 °C). The primary TEM observations revealed the presence of Ta nanodispersions in the as-received condition which has been observed to contribute to dramatic strengthening and exceptional thermal stability when the alloy is subjected to extreme conditions. Also, deformation induced coherent and incoherent twin boundaries are observed and the twin density reduces with increasing temperature relative to the 25 °C strained case. Furthermore, dislocation activity is observed inside a few large parent phase grains. Such microstructural changes contribute to the observed flow stress at high strain rates coupled with high temperatures where both twinning and dislocation based mechanisms contribute towards the plastic deformation of such alloys.
Symposium Organizers
Gianguido Baldinozzi, Paris-Saclay University
David Andersson, Los Alamos National Laboratory
Chaitanya S. Deo, Georgia Institute of Technology
Michael R. Tonks, Pennsylvania State University
MD8.11: Advanced Fuel Designs II
Session Chairs
David Andersson
Maulik Patel
Friday AM, April 01, 2016
PCC West, 100 Level, Room 106 B
9:15 AM - *MD8.11.01
Microstructural Modeling and Characterization of Nuclear Materials at Extreme Burn-Up
Melissa Teague 1,Michael Tonks 2,Bradley Fromm 3,Stephen Novascone 3
1 Sandia National Laboratories Albuquerque United States,2 Penn State State College United States3 Idaho National Laboratory Idaho Falls United States
Show AbstractCurrently, reactor performance is largely constrained by the limitations of the
materials involved in these reactors. The fuel is particularly limiting due to fission gas
generation, changes in thermal conductivity, microstructure changes within the fuel, fuel
swelling, and fuelcladding chemical interaction (FCCI). The fuel cladding is also under extreme temperature and dose, in excess of 150 DPA for some samples. Highly irradiated fuel is radially inhomogeneous in composition, microstructure, and temperature. In this work, high burnup
mixed oxide fuel with local burnups of 3.4-23.7% FIMA were destructively examined as part of a
research project to understand the performance of oxide fuel at extreme burnups. Optical
metallography, transmission electron microscopy and electron back-scatter diffraction were
performed to further study the microstructure and chemical composition of the irradiated fuel and cladding
.
The optical micrographs were used to generate finite-element meshes in order to model the
effective thermal conductivity of the irradiated fuel as a function of burnup, radial position, and
temperature.
The fueltocladding gap closed significantly in samples with burnups below 7-9% FIMA.
Samples with burnups in excess of 7-9% FIMA had a reopening of the fueltocladding gap and
evidence of joint oxidegain formation. Additionally, high burnup structure was observed in the
two highest burnup samples (23.7 and 21.3% FIMA). The microstructural modeling of the
effective thermal conductivity found close (10-20%) agreement between the calculated effective
thermal conductivities and the semiempirical based analytical models, validating the finite-
element mesoscale approach to microstructural modeling of effective thermal conductivities in
irradiated fuel.
9:45 AM - MD8.11.02
Phase Field Modeling of Grain Growth in UO2
Karim Ahmed 1,Yongfeng Zhang 1,Xianming Bai 1,Cody Permann 1,Bulent Biner 1,Todd Allen 1,Michael Tonks 2,Anter El-Azab 3
1 Idaho National Laboratory Idaho Falls United States,2 Pennsylvania State University State College United States3 Purdue University West Lafayette United States
Show AbstractWe present an elaborate phase field model for investigating the grain growth process in porous UO2. The model takes into account the interactions between pores and grain boundaries, which strongly affect the grain growth kinetics. Moreover, the model takes into consideration the effect of anisotropy in surface and grain boundary energies and mobilities and the effect of temperature gradients on the kinetics of grain growth. Furthermore, using a formal asymptotic analysis, the phase field model was matched to its sharp-interface counterpart and all the model parameters were uniquely determined. Therefore, the model is able to obtain accurate growth rates that can be compared with experiments. The simulations of the model are carried out using MARMOT, the mesoscale simulator developed at Idaho National Laboratory. The model is used to quantify the effect of pore drag on the kinetics of grain growth in UO2. The effects of pore fraction and configurations, anisotropy of thermodynamic and kinetic parameters, and temperature gradient on the grain growth process were investigated.
10:00 AM - MD8.11.03
Atomistic Understanding of Ordering in U-Zr Alloys
Alex Moore 1,Chaitanya Deo 1,Michael Baskes 4,Maria Okuniewski 5
1 Georgia Inst of Technology Atlanta United States,2 Mississippi State University Mississippi State United States,3 University of California San Diego United States,4 Los Alamos National Laboratory Los Alamos United States5 Idaho National Laboratory Idaho Falls United States
Show AbstractThis research uses an atomistic approach to study microstructural morphology and evolution, to investigate how temperature and alloy concentration affect ordering. A semi-empirical Modified Embedded Atom Method (MEAM) is used to describe Uranium and Zirconium interactions. Interactions are simulated using molecular dynamics (MD) and Monte Carlo (MC) methods to investigate the properties and equilibrium configurations of the high temperature body-centered-cubic (bcc) uranium-zirconium (U-Zr) alloys, the fundamental metallic alloy fuel for the next generation of fast nuclear reactors. This setup is able to successfully replicate some of the base thermo-physical and microstructural characteristics seen during fabrication and irradiation of the U-Zr metallic fuels. These simulations aid the fundamental understanding of the microstructure evolution of U-Zr alloys, which has proven to be complex and has not been well understood. The MEAM potential shows the thermodynamic driving force to the lamellar structure for the melt-casted uranium-rich alloys and the finely acicular microstructure of the water quenched uranium-rich alloys seen experimentally. In addition, when the uranium-rich U-Zr alloy is equilibrated at a lower temperature, the lamellar/acicular microstructures begin to spheroidize as seen in experiments. In the intermediate region, the ordering seen is able to facilitate the structure to the partially ordered δ-UZr2 phase seen experimentally. Lastly, the zirconium-rich region is able to successfully show the thermodynamic driving force to the acicular, Widmanstätten, and martensitic needles type microstructures seen experimentally.
10:15 AM - *MD8.11.04
Electronic Structure Calculations in Support of Separate Effect Experiments for the Study of Irradiation Effects in Nuclear Ceramics
Marjorie Bertolus 1,Julia Wiktor 1,Emerson Vathonne 1,Rene Bes 1,Philippe Martin 1,Marie-France Barthe 2,Gerald Jomard 1,Michel Freyss 1
1 CEA, DEN St Paul-Lez-Durance France,2 CNRS/CEMHTI Orléans France
Show AbstractDuring in-reactor irradiation, actinide fission produces large quantities of defects and fission products, which have a significant influence on the structural, thermal and mechanical properties of nuclear fuels and claddings. A better understanding of atomic transport (self-diffusion and diffusion of fission gases) in these materials is central to getting further insight into the irradiation driven micro-structural changes.
An efficient approach to unravel basic mechanisms is to couple separate effect experiments and modelling at the atomic scale. We will present two examples of investigations where electronic structure calculations coupled to experimental observations have yielded a better understanding of defect and fission gas behaviour in nuclear ceramics.
We will first show the application of the two component density functional theory (TCDFT) to the interpretation of positron annihilation spectroscopy (PAS) results. This has enabled to identify equilibrium and irradiation induced defects in silicon carbide (SiC) [1,2,3] and uranium dioxide (UO2) [3,4].
We will then present the use of the results of electronic structure calculations in the DFT+U framework as input for X-ray absorption spectroscopy (XAS) spectra simulations to identify the most favourable incorporation site for fission gases (xenon and krypton) in ion-irradiated UO2 [5,6].
[1] J. Wiktor, G. Jomard, M. Torrent, M. Bertolus, Phys. Rev. B 87, 235207 (2013)
[2] J. Wiktor, X. Kerbiriou, G. Jomard, S. Esnouf, M.-F. Barthe, M. Bertolus, Phys. Rev. B 89, 155203 (2014)
[3] J. Wiktor, Ph.D., Université Aix-Marseille (2015)
[4] J. Wiktor, G. Jomard, M. Torrent, M.-F. Barthe, M. Freyss, M. Bertolus, Phys. Rev. B 90, 184101 (2014)
[5] R. Bès, P.M. Martin, E. Vathonne, R. Delorme, C. Sabathier, M. Freyss, M. Bertolus, P. Glatzel, Appl. Phys. Lett. 106, 114102 (2015)
[6] P.M. Martin, E. Vathonne, G. Carlot, R. Delorme, C. Sabathier, M. Freyss, P. Garcia, M. Bertolus, P. Glatzel, O. Proux, J. Nucl. Mater. 466, 379 (2015)
MD8.12: Complex Behaviors in Ceramics
Session Chairs
Gianguido Baldinozzi
Marjorie Bertolus
Alex Moore
Friday PM, April 01, 2016
PCC West, 100 Level, Room 106 B
11:15 AM - MD8.12.01
Ordered Atomic Arrangements and Electron Charge Density in La6UO12
Luis Casillas 1,Kurt Sickafus 1,Gianguido Baldinozzi 2
1 Univ of Tennessee Knoxville United States,2 Materials Science Paris-Saclay Paris France
Show AbstractUranium-rare earths complex compounds are important materials in nuclear energy, they are considered as possible waste forms for actinide disposal. Many of those compounds have structures related to the ideal fluorite. Depending on composition and annealing conditions, long- or intermediate-range ordering may occur in these compounds. In this respect, some of these structures may be good candidates for enhancing chemical stability and for accommodating large quantities of defects (substitutional, vacancies, interstitials, …). Interestingly, high solubility of rare earth elements is desirable in nuclear fuels because they constitute a significant fraction of the isotopes produced by fission. In this work, we examine the structural flexibility of the (La,U)O2±x system, with a particular focus on a compound with stoichiometry, La6UO12. Numerous oxides with this 6:1:12 stoichiometry exhibit highly-ordered structures that are derivatives of the fluorite (CaF2) structure. They are typically referred to in the literature as delta (δ) phase compounds. Anion and cation ordering in La6UO12 might occur in a number of different ways. We have explored several possible ordered structures, which we derived using a symmetry group-subgroup theory approach. Different ordering patterns for the anions and cations lead to different electronic structures. To discuss these differences and their specific features in a quantitative way, we have assessed and applied AIM-type tools to the electron charge density obtained by DFT for each of our postulated structures, and obtained robust estimates for Bader’s charges and the characteristics of the critical points of the Laplacian of the charge density.
11:30 AM - MD8.12.02
Thin Film Samples: A New Methodology to Investigate the Fission Gas Release Mechanisms in Nuclear Fuel
Guillaume Brindelle 1,Helene Capdevila 1,Yves Pontillon 1,Lionel Desgranges 1,Gianguido Baldinozzi 2
1 CEA, DEN, DEC, Cadarache St. paul les durance France,2 SPMS, LRC Carmen, CNRS CentraleSuplec Châtenay-Malabry France
Show AbstractPredicting accurately fission gas release (FGR) from high burn up fuels during off-normal conditions, such as a loss of coolant accident (LOCA), remains a significant and important challenge. A clear progress would be to identify and evaluate the basic mechanisms promoting this FGR.
In the upper temperature range, 1100°C to 1200°C, previous experimental work has already been performed with specific dedicated annealing tests, measuring the FGR kinetics, combined with post-tests fuel microstructural examinations. For fuels up to 70GWd/t under simulated LOCA conditions, the main outcome is that gas from the release burst mainly originates from gas accumulated at grain boundaries during base irradiation.
In the lower temperature range, below 1000°C, no particular FGR mechanism has been clearly established. Recent results on irradiated fuel suggest that grain boundary rupture does not occur significantly. To further progress, this work aims at evaluating two complementary mechanisms which could be involved during the accident: defects annealing and mechanical stress release. The main goal of this paper is to highlight how these FGR mechanisms, in the 600-800°C temperature range, can be studied thanks to thin film samples. The methodology consists in creating different states of defects in simulated samples and to study their influence on gas migration.
We believe that an interesting way to gain further understanding of those basic mechanisms is to separate these effects and to perform irradiations on materials simulating the nuclear fuel having thin film geometry. Mesoporous or dense CeO2 and UO2 model materials were selected for these studies, optimizing the film thickness to separate the effects of damage and implantation of heavy ions and specifically separating the mechanical stress related to the creation of defects from those related to ion implantation. Differences between UO2 thin films and CeO2 ones will be discussed to assess the accuracy of CeO2 films as a surrogate of nuclear fuel, focusing on the specific manufacturing characteristics. Sample characterization will be performed by glancing angle X-ray diffraction to analyze the microstructure and measure the strain existing in those films. Results will be discussed and compared to gas release models in irradiated fuel.
11:45 AM - MD8.12.03
Examination of Complex Fission Products and Selective Materials Transport in TRISO Coated Particles
Terry Holesinger 1,Isabella van Rooyen 2
1 Los Alamos National Laboratory Los Alamos United States,2 Fuels Performance and Design Idaho National Laboratory Idaho Falls United States
Show AbstractHigh resolution electron microscopy investigations of selected coated particles from the first advanced gas reactor experiment (AGR-1) at Idaho National Laboratory has provided important information on the fission product distribution and chemical composition within the SiC and inner pyrolytic carbon layers and the interface between them. Particles from AGR-1 were irradiated to an average burn-up of 15.3% fissions per initial metal atom, time-averaged, volume-averaged temperature of 1092°C, a time-averaged, peak temperature of 1166°C, and an average fast fluence of 3.22x1025 n/cm2. Of particular concern is the release of silver from the particles. Recent observations have suggested that grain-boundary transport is a primary method for Ag transport through the SiC. However, the complex phases that the fission products comprise and their combined role in governing mass transport through the TRISO layers require further understanding. This report describes detailed, high-resolution analytical electron microscopy studies of fission product movement through the TRISO layers with a particular emphasis on the microstructural aspects related to Ag transport.
12:00 PM - MD8.12.04
Molecular Dynamic Simulations of the Coupled Effects of Electronic and Nuclear Energy Loss in Ion Irradiation
Eva Zarkadoula 1,Yanwen Zhang 1,William Weber 1
1 Oak Ridge National Laboratory Oak Ridge United States,2 Materials Science and Engineering University of Tennessee Knoxville United States,1 Oak Ridge National Laboratory Oak Ridge United States
Show AbstractElectronic effects are of significant importance in a wide variety of fields where high energy irradiation processes take place, including nuclear applications, the semiconductor industry and material characterization. We use MD simulations in combination with the inelastic thermal spike model to study the combined effects of the nuclear and the electronic energy loss on the damage production due to ion irradiation in ceramics. We investigate the role of pre-existing disorder in nanoscale ion track formation in SrTiO3 and we find a significant synergy between the inelastic and elastic energy loss. These findings are in agreement with experimental results and our results reveal the ion track formation mechanism in this material. Additionally we investigate the role of the electronic effects during Kr and Xe ion irradiation of ZrSiO4, finding that the electronic energy loss has additive impacts in the damage production, which can explain the amorphization efficiency of these ions in previously reported experimental results.
Our work highlights the importance of the electronic effects and the need to take them into account in order to approach irradiation effects in a more realistic way and predict the materials’ performance under irradiation.
This work was supported by the U.S. DOE, BES, MSED.
12:15 PM - MD8.12.05
Atypical Phase Change in Gd2O3 Epitaxial Layers under Ion Irradiation
Najah Mejai 2,Aurelien Debelle 1,Lionel Thome 1,Gael Sattonnay 1,Dominique Gosset 3,Alexandre Boulle 2
2 Science des Procedes Ceramiques et de Traitements de Surface Centre Europeen de la Ceramique, Univ. Limoges, CNRS Limoges France,1 CSNSM Univ Paris-Sud, CNRS, Universite Paris-Saclay Orsay Cedex France3 DEN-DMN-SRMA-LA2M CEA-Saclay Gif/Yvette France
Show AbstractRare Earth Oxide (REO) based materials are used in, or are contenders for numerous settings in materials science. For instance, they are studied for nuclear energy applications such as nuclear waste forms, strengthening elements in ODS steels and solid-state neutron detectors. As thin epitaxial layers, they represent, intrinsically or after ion doping, possible high-k gate dielectrics for metal-oxide-semiconductor devices; they can also be buffers for growth of alternative semiconductors, the choice of which depends on the phase of the REO underneath. For all these applications, an understanding of the behavior of these materials under ion irradiation is of upmost interest. A few studies have been conducted on some irradiated polycrystalline REOs (namely Gd
2O
3, Er
2O
3, Dy
2O
3, Y
2O
3), and the main result is that the initial cubic structure is not stable and transforms into a monoclinic structure. However, no study has been carried out so far on model, single-crystal-like materials and no complete phase-change kinetics has been reported.
In the present work [1], we studied high crystalline-quality Gd
2O
3 epitaxial layers deposited on silicon. These layers were irradiated with 4 MeV Au
2+ ions in a broad fluence range (from 2.5x10
13 to 5x10
15 cm
-2). We used ion channeling, X-ray diffraction and Raman spectroscopy to monitor the irradiation-induced effects. Results show that a cubic-to-monoclinic phase change also takes place in these layers. More strikingly, the phase change is found to be depth dependent, whereas the energy deposition profile is constant. A defect migration towards the surface is invoked to explain this finding. Besides, the phase-change kinetics follows a two-step process. An XRD analysis shows that the monoclinic layer is nanocrystalline. Therefore, it is suggested that defect accumulation in the near-surface region occurs in the first step, generating highly disordered, energetically unstable nanometer-scale regions. The release of the corresponding stored energy takes place through a phase transition in the second step.
N. Mejai, A. Debelle, L. Thomé, G. Sattonnay, A. Boulle, D. Gosset, R. Dargis, A. Clark, Appl. Phys. Lett. 107
(2015) 131903.
12:30 PM - MD8.12.06
Investigations of the Mechanical and Hydrothermal Stabilities of SBA-15 and Al-SBA-15 Mesoporous Materials
Dayton Kizzire 1,Sonal Dey 2,Hayley Osman 1,Robert Mayanovic 1,Ridwan Sakidja 1,Zhongwu Wang 3,Manik Mandal 4,Kai Landskron 4
1 Missouri State University Springfield United States,1 Missouri State University Springfield United States,2 Colleges of Nanoscale Science and Engineering State University of New York Polytechnic Institute Albany United States3 Cornell University Ithaca United States4 Department of Chemistry Lehigh University Bethlehem United States
Show AbstractPeriodic mesoporous materials possess high surface to volume ratio and nano-scale sized pores, making them potential candidates for heterogeneous catalysis, ion exchange, gas sensing and other applications. In this study, we use in situ small angle x-ray scattering (SAXS) and molecular dynamics (MD) simulations to investigate the mechanical and hydrothermal stability properties of periodic mesoporous SBA-15 silica and SBA-15 type aluminosilica (Al-SBA-15) to extreme conditions. The mesoporous SBA-15 silica and Al-SBA-15 aluminosilica possess amorphous frameworks and have similar pore size distribution (pore size ~9-10 nm). The in situ SAXS measurements were made at the B1 beamline, at the Cornell High Energy Synchrotron Source (CHESS). The mesoporous SBA-15 silica and Al-SBA-15 aluminosilica specimens were loaded in a diamond anvil cell (DAC) for pressure measurements, and, separately, with water in the DAC for hydrothermal measurements to high P-T conditions (to 280 °C and ~ 200 MPa). Analyses of the pressure-dependent SAXS data show that the mesoporous Al-SBA-15 aluminosilica is substantially more mechanically stable than the SBA-15 silica. Hydrothermal measurements show a small net expansion of the pores at elevated P-T conditions, due to dissolution of water into the pore walls. Under elevated P-T conditions, the Al-SBA-15 aluminosilica shows significantly greater hydrothermal stability than the SBA-15 silica. Our MD simulations show that the bulk modulus value of periodic mesoporous SBA-15 silica varies exponentially with percentage porosity. Molecular dynamics simulations are being made in order to better understand how the pore architecture and the chemical composition of the host structure govern the stability properties of the mesoporous materials.
12:45 PM - MD8.12.07
Understanding the Gas Sensing Ability of (Zn,Co)Ga2O4 Thin Films via Optical, Thermal Transport and DC Conductivity Measurements
Musa Mutlu Can 1,Shalima Shawuti 1,Namik Akcay 1,Gokhan Algun 1
1 Istanbul University Istanbul Turkey,
Show AbstractThe past 20 years developments on various applications, such as diots, optical power out, transparent electrods, izolation materials on glass, LCD secreen and smart windows, in oxide semiconductor technology have been developed [King, 2011]. Finding new physical properties cause an increase recent studies on oxide semiconductors. Because of having wide band gap, oxide semiconductors are excellent transparent (> 90%) in the range of UV region and IR regions. In the past the wide band gap of oxide semiconductors was considering as a disadvantage for conductivity, nowadays it is realized that the low formation entalpy of point defects in oxide semiconductors cause a conductivity at the oxide semiconductors. The point defects generated in the crystal lattice of the oxide semiconductor allow formation of shallow and deep energy levels. Formed new energy levels causes increased number of free electrons in the lattice and allows the new electronic transitions. Those newly acquired electronic configuration will help the development on the optoelectronic devices.
We focus on zinc gallate (Zn,Co)Ga2O4 oxide semiconductors, which have limited study on. (Zn,Co)Ga2O4 are direct band gap semiconductors with value 4.4 – 4.7 eV (at room temperature) [López, 2014; Oshima, 2014], transparent to the visible light and high refractive index materials [Oshima, 2014]. The physical properties make (Zn,Co)Ga2O4 semiconductors be suitable for applications in solar cells, gas sensors, chemical sensors, surface acoustic wave, pressure sensors, transparent conductive, anti-reflective coating and luminescent materials. The aim of this study is to show the point defects dependent gas (H2 and O2) sensing ability above the room temperature and opto electronic behavior of ZnGa2O4 thin films, fabricated via RF magnetron sputtering system. The sensing ability were perfomed with temperature dependent I-V and C-V curves. Furthermore, the post deposition annealing atmosphere were changed to manage the point defect amounts and types in thin films. The study include investigation of structural characterization (XRD, SEM, XPS, FTIR ..etc) of (Zn,Co)Ga2O4 semiconductors and point defects dependent physical property variation (optical, thermal transport and DC conductivity). (Zn,Co)Ga2O4 crystal structure usually has n-type structure. Oxygen vacancies (Vo), interstitial Zn (Zni) and Ga (Gai) atoms or oxygen sub-lattice in the Zn or Ga atoms (Zno or Gao) are the origin of n-type behavior [King, 2011; Li, 2014; Oshima, 2014].
[1] King, P. D. C., et.al., (2011), J. Phys.: Condens. Matter., 23, 334214.
[2] Oshima, et.al., (2014), Journal of Crystal Growth, 386, 190–193.
[3] López, et. al. (2014) , Materials Research Express 1, 025017
MD8.13: Strain and Radiation Effects in Insulators
Session Chairs
Luis Casillas
Melissa Teague
Friday PM, April 01, 2016
PCC West, 100 Level, Room 106 B
2:30 PM - *MD8.13.01
Mesoscale Modeling of Laser-Induced Crystallization of Amorphous Ge
Luis Sandoval 1,Celia Reina 2,Jaime Marian 3
1 Los Alamos Los Alamos United States,2 University of Pennsylvania Philadelphia United States3 Univ of California- Los Angeles Los Angeles United States
Show AbstractFast and repeatable transitions between the crystalline and amorphous solid phases of so-called GST materials are the basis for storing large amount of information in rewritable devices in the electronics industry. In GST systems, the Ge matrix enables fast transitions when stimulated via heat discharges and thus glassy-to-rystalline phase transformations in pure Ge have been the subject of many experimental works. In particular, observations made with ultrafast time-resolved electron microscopy reveal a complex micorstructure characterized by several distinct crystallization regimes. In this work, we present a mesoscale model based on a phase field microstructural simulator fitted entirely to atomistic calculations, including bulk and interfacial free energies, as well as interface mobilities, to simulate Ge recrystallization under laser-spot heating. In addition, we perform direct molecular dynamics simultions of the growth of nanoscale crystalline Ge grains embedded in a glassy Ge matrix. These simulations provide valuable physical insights that we then use to inform the mesoscale simulator to enhnce its fidelity. This atomistically-informed mesoscale approach is then employed to simulate Ge crystallization under laser-spot heating conditions. We discuss the impact on the results of the nucleation rate and compare the simulated timescales to experimental measurements.
3:00 PM - MD8.13.02
Radiation Defect Dynamics in SiC
Leonardus Bimo Bayu Aji 1,Joseph Wallace 2,Aiden Martin 1,Lin Shao 2,Sergei Kucheyev 1
1 Lawrence Livermore National Lab Livermore United States,1 Lawrence Livermore National Lab Livermore United States,2 Nuclear Engineering Texas Aamp;M University College Station United States2 Nuclear Engineering Texas Aamp;M University College Station United States
Show AbstractSilicon carbide is a prototypical nuclear ceramic material. It is also attractive for high-temperature electronics applications. Understanding radiation damage processes in SiC is crucial for exploiting unique properties of this material in both nuclear and electronics applications. Above room temperature, the buildup of radiation damage in SiC is a dynamic process governed by the mobility and interaction of ballistically-generated point defects. The mechanism of defect interaction processes, however, remains poorly understood.
Here, we use a novel pulsed ion beam method to study radiation defect dynamics in SiC (3C and 4H) bombarded with 500 keV Ar ions in the temperature range of 25 - 250 °C. Results reveal that the defect recombination efficiency monotonically increases with temperature. In contrast, the defect lifetime (and, hence, the defect relaxation rate) exhibits a non-monotonic temperature dependence with a maximum of ~5 ms at ~100 °C, indicating a change in the dominant defect interaction mechanism at this temperature. For the 150-250 °C range, the dominant defect relaxation process has an activation energy of 0.25 eV. In contrast to the strong temperature dependence of the defect lifetime, the defect diffusion length exhibits a weak temperature dependence, reflecting a weak temperature dependence of the concentration of defect traps. These results have important implications for understanding and predicting radiation damage in SiC and for the development of radiation-resistant materials via interface-mediated defect reactions.
This work was performed under the auspices of the US DOE by LLNL under contract DE-AC52-07NA27344.
3:15 PM - MD8.13.03
Pulsed Ion Beam Study of Radiation Defect Dynamics in Gallium Arsenide
Aiden Martin 1,Joseph Wallace 2,Leonardus Bimo Bayu Aji 1,Lin Shao 2,Sergei Kucheyev 1
1 Lawrence Livermore National Laboratory Livermore United States,1 Lawrence Livermore National Laboratory Livermore United States,2 Department of Nuclear Engineering Texas Aamp;M University College Station United States2 Department of Nuclear Engineering Texas Aamp;M University College Station United States
Show AbstractInteraction of energetic ions with crystalline solids leads to lattice disorder which degrades material quality. Formation of stable ion induced structural defects often proceeds via so called dynamic annealing, involving the diffusion and interaction of mobile point defects. While critically important for understanding ion induced defect generation, this dynamic regime of defect evolution after the thermalization of ion collision cascades remains poorly understood for most materials.
Gallium arsenide is a direct bandgap semiconductor with high resistance to radiation damage, making it ideal for applications in extreme environments. However, little is known about the mechanisms of dynamic annealing in gallium arsenide. Here, a pulsed ion beam method is used to study radiation defect dynamics in gallium arsenide. Specifically, we use a pulsed 500 keV Ar ion beam to determine the characteristic time constant (τ) and diffusion length (Ld) of dynamic annealing in gallium arsenide over a temperature range from -20 to 80 °C, enabling the determination of the activation energy of the dominant dynamic annealing process. Our results elucidate the dynamic annealing characteristics of gallium arsenide and demonstrate the utility of the pulsed ion beam method in measuring dynamic annealing characteristics in a range of technologically important materials.
This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.
3:30 PM - MD8.13.04
Formation of Dynamic Topographic Patterns during Electron Beam Induced Etching of Diamond
Aiden Martin 2,Alan Bahm 2,James Bishop 2,Igor Aharonovich 2,Milos Toth 2
1 Lawrence Livermore National Laboratory Livermore United States,2 University of Technology, Sydney Broadway Australia,3 FEI Company Hillsboro United States,2 University of Technology, Sydney Broadway Australia2 University of Technology, Sydney Broadway Australia
Show AbstractSpontaneous formation of complex geometric patterns is an interesting phenomenon that provides fundamental insights into underlying roles of symmetry breaking, anisotropy and non-linear interactions. Here we present dynamic, highly ordered topographic patterns on the surface of diamond that span multiple length scales and have a symmetry controlled by the chemical species of a precursor gas used in electron beam induced etching (EBIE).
We provide an anisotropic etch rate kinetics model that fully explains the observed patterns, and reveals an electron energy transfer pathway that has been over-looked by existing EBIE theory. We therefore propose a fundamental modification, whereby the critical role of energetic electrons is to transfer energy to surface atoms of the solid rather than to surface-adsorbed precursor molecules.
EBIE is a high resolution, direct-write nanofabrication technique in which a precursor gas and an electron beam are used to realize etching. A key advantage of EBIE is the ability to etch materials such as diamond that are resistant to conventional chemical etch processes, without introducing damage to the substrate as observed in ion sputtering techniques. As a result, EBIE has recently been used to fabricate components for photonic and electronic applications. Our findings can be harnessed to engineer specific surface patterns under various electron beam irradiation environments for controlled wetting, optical structuring and other emerging applications that require nano and micro-scale surface texturing.
A portion of this work was funded by FEI Company and the Australian Research Council (Project Number DP140102721). A portion of this work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344. I.A. is the recipient of an Australian Research Council Discovery Early Career Research Award (Project Number DE130100592).
3:45 PM - MD8.13.05
Structure-Modified Stress Behaviour by Ion Irradiation in Carbon Nanostructures for Field Emission Applications
Himani Sharma 4,Mohit Sharma 2,Dinesh Agarwal 3,A.K. Shukla 4,D.K. Avasthi 3,V.D. Vankar 4
1 Doon University Dehradun India,4 Thin Film Laboratory, Indian Institute of Technology Delhi, India New Delhi India,2 Institute of Materials Research and Engineering, 3 Research Link Agency for Science,Technology and Research (A*STAR) Singapore Singapore3 Inter University Accelerator Centre (IUAC), New Delhi, India New Delhi India4 Thin Film Laboratory, Indian Institute of Technology Delhi, India New Delhi India
Show AbstractThe development of the carbon-based nanostructures such as graphene and carbon nanotubes (CNTs) for various advanced technological applications including nanoelectronics, and field-emission display devices are based on the methods to modify these carbon nanosystems with definitiveness. Various methods such as grafting, doping, functionalization, and mechanical strain have been used to modify these unique structures for electron field applications. Apart from these methods, the modification by ions is one such method that can be employed for precise alteration and tailoring of CNTs and graphene, resulting in some beneficial effects.
The structure modification under stress behaviour and ion irradiation conditions have been depicted. Ion irradiation has been explored as a tool to tailor the structure and electron mission properties on CNTs and multilayer graphene (MLGs) as a function of wall thickness.
In the present work, possibility of achieving enhanced electron field-emission properties of stress-induced carbon nanotubes (CNTs) and multilayer graphene (MLGs) by ion modification is investigated. CNTs and MLGs are synthesized by microwave plasma enhanced chemical vapour deposition. Micro-Raman spectroscopy is used as a potent technique for in-depth investigations of stress induced CNTs and MLGs. It is found that iron used as a catalyst, compresses at particular fluence and induces stresses in CNTs and MLGs to modify these structures, supported by high-resolution transmission electron microscopy (HRTEM) studies. The stresses are explained by the buckling wavelength.
The structural modification in carbon nanostructures is well related to the electron field emission properties Furthermore, the stresses induced in exotic nanostructures are studied for investigating wetting properties, which are well-corroborated with electron emission characteristics. It is found out that less-wetted CNTs and MLGs display enhanced emission properties with turn-on voltages of 1.4 and 2.6 V/μm, respectively, in comparison to hydrophilic CNTs and MLGs with turn-on voltages of 2.8 and 3.4 V/μm, respectively.
References:
(1) Wei, J.; Jia, Y.; Shu, Q.; Gu, Z.; Wang, K.; Zhuang, D.; Zhang, G.;Wang, Z.; Luo, J.; Cao, A.; Wu, D. Double-Walled Carbon Nanotube Solar Cells. Nano Lett. 2007, 7, 2317−2321.
(2) Sharma, H.; Agarwal, D. C.; Sharma, M.; Shukla, A. K.; Avasthi, D. K.; Vankar, V. D. Tailoring of Structural and Electron Emission Properties of CNT Walls and Graphene Layers Using High-Energy Irradiation. J. Phys. D: Appl. Phys. 2013, 46, 315301−315308.
(3) Misra, A.; Tyagi, P. K.; Rai, P.; Mahopatra, D. R.; Ghatak, J.;Satyam, P. V.; Avasthi, D. K.; Misra, D. S. Axial Buckling and Compressive Behavior of Nickel-Encapsulated Multiwalled Carbon Nanotubes. Phys. Rev. B 2007, 76, 014108−014113.
MD8.14: Materials Performing in Harsh Environments
Session Chairs
Jaime Marian
Michael Tonks
Friday PM, April 01, 2016
PCC West, 100 Level, Room 106 B
4:30 PM - MD8.14.01
Failure Mechanisms of Fiber Optic Temperature Sensors in High Temperature and Vibration Environments
Loucas Tsakalakos 1,Uttara Dani 1,Boon Lee 1,Susanne Lee 1,Sudeep Mandal 1,Vincent Smentkowski 1,Sunilkumar Soni 1
1 GE Global Research Niskayuna United States,
Show AbstractFiber optic temperature sensors are used in a variety of harsh environment applications. We have explored use of such temperature sensors in commercial gas turbines to measure the temperature various regions of interest within the turbine system. More specifically, fiber optic temperature rakes were designed and installed on a commercial gas turbine under full load conditions. This work will focus on failure mechanisms observed at multiple length scales that impact the performance of high temperature optical fiber sensors. It was found that Au-coated silica fibers, which are a standard in the industry, undergo various failure modes when subjected to combinations of high temperature and high vibration. More specifically, the Au coating becomes soft/ductile as the temperature is increased. We also observed that the Au coating is not well bonded to the silica fiber, as expected since there are no adhesion layers present. These effects lead to significant damage of the fiber optic under high vibrations. We also found that vibrations from the gas turbine couple into fundamental modes of the fiber optic probe assembly, which was analyzed by detailed dynamic mechanical analysis. This led to the fiber impacting the internal wall of the probe assembly, which caused further damage and failure of the fiber and the Au coating. The silica fibers returned from the field also exhibited significant twisting throughout most of their length. This suggests the fibers reached temperatures above their strain point (about 1000 C for pure silica glass) which is explained by either a) the strain point has been significantly reduced by the presence of the Ge dopant, or b) the temperature was higher than expected in the gas turbine exhaust region. It was also hypothesized that complex anelastic effects may play a role under the high temperature, high vibration environment experienced by the probes. Detailed structural analysis of the fiber optic temperature sensors by scanning electron microscopy, TOF-SIMS, and X-ray microscopy will be presented to corroborate the above simulations and proposed damage mechanisms. Finally, we note that the fiber Bragg gratings (FBG) present within the temperature probes provided promising temperature data, and were in fact not damaged/erased by the high temperature environment.
4:45 PM - MD8.14.02
Nanosecond Homogeneous Nucleation and Crystal Growth in Shock-Compressed SiO2
Yuan Shen 1,Shai Jester 1,Tingting Qi 1,Evan Reed 1
1 Stanford Univ Stanford United States,
Show AbstractUnderstanding the kinetics of shock-compressed SiO2 is of great importance for mitigating optical damage for high-intensity lasers and for understanding meteoroid impacts. Experimental work has placed some thermodynamic bounds on the formation of high-pressure phases of this material, but the formation kinetics and underlying microscopic mechanisms are yet to be elucidated. Here, by employing multiscale molecular dynamics studies of shock-compressed fused silica and quartz, we find that silica transforms into a poor glass former that subsequently exhibits ultrafast crystallization within a few nanoseconds. We also find that, as a result of the formation of such an intermediate disordered phase, the transition between silica polymorphs obeys a homogeneous reconstructive nucleation and grain growth model. Moreover, we construct a quantitative model of nucleation and grain growth, and compare its predictions with stishovite grain sizes observed in laser-induced damage and meteoroid impact events.
5:00 PM - MD8.14.03
ZrB2 and h-BN Composite Thin Films for Use in Harsh Environments Above 1000°C
David Stewart 1,Julia Sell 2,Robert Meulenberg 1,Robert Lad 1
1 University of Maine Orono United States,2 University of Maryland College Park United States
Show AbstractThere is a critical need to strategically deploy sensors on industrial equipment such as turbines, compressors, and boilers operating in harsh environments above 1000°C in order to improve their safety, efficiency, and reliability. However, the development of small, robust, wireless sensor devices to operate in such environments is hampered by the lack of morphologically and chemically stable thin films that can be used as electrodes and other electronic components in such environments. At micron length scales relevant for electronic devices, commonly stable thin film materials such as Pt are thermodynamically driven to agglomerate and dewet the substrate at temperatures above 700°C, thereby eliminating electrically conductive pathways. To improve film stability, nanolaminates comprised of Pt and Zr layers were grown on sapphire substrates, and these films have been tested at temperatures between 800–1300°C in air. Upon high temperature oxidation, ZrO2 nanograins are formed and they serve to hinder the agglomeration of Pt grains on a sapphire substrate. As an alternative material, zirconium diboride (ZrB2) is an ultra-high temperature ceramic with metallic-like electrical conductivity and is well known to be a stable bulk material in reducing environments. ZrB2 thin films less than 300 nm thick have been grown on sapphire using e-beam evaporation and they were found to be morphologically and electrically stable at least to 1000°C in vacuum, and they exhibit very little grain growth over time. EXAFS analysis of the films reveals nanoscale crystallographic structure very similar to that of bulk ZrB2, despite limited long-range order. When annealed in air, however, ZrB2 quickly oxidizes to ZrO2 and the film becomes insulating. Thus, a capping layer strategy has been adopted, wherein the ZrB2 films are protected from oxidation by either an extremely thin (<50 nm) amorphous Al2O3 layer grown by ALD or a crystalline h-BN layer grown by sputter deposition. The low rate of oxygen diffusion in Al2O3 retards film oxidation, and theoretical and experimental work reported in the literature has demonstrated that h-BN is extremely oxidation resistant at high temperatures. Pt-Zr and ZrB2 thin films on sapphire substrates employing these Al2O3 and h-BN capping layers have been tested at temperatures up to 1300°C under varying levels of oxygen exposure in order to characterize the early stages of oxidation. The results indicate that the capping layer strategy is crucial in order to utilize ZrB2 films in oxidizing environments.