bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical Properties of E21 Ti3AlC-base Alloy
Authors: Hosoda Hideki , Inamura Tomonari , Wakashima Kenji 
Published: June 2019

AbstractMechanical properties and phase constitution of an E21-type Ti3AlC-base alloy were investigated by compression tests in a temperature range from room temperature (RT) to 1273K, scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The unit cell of E21 Ti3AlC is constructed by ¡§L12 Ti3Al¡¨ and a carbon atom occupying the body-center octahedral-interstitial-site surrounded by the Ti atoms. The nominal composition of the alloy was chosen to be the stoichiometric composition of 60mol%Ti-20mol%Al-20mol%C. The alloy was synthesized by mechanical alloying using high purity elemental powders followed by hot pressing at 1473K for 3hrs. It was found by XRD and SEM that the alloy was mainly composed of E21 Ti3AlC in addition to Cr2AlC-type Ti2AlC precipitates as a second phase. The density of Ti3AlC is calculated to be 4.29g/cm3 based on the lattice parameter of 0.4134nm of E21. The average grain size was 2μm by SEM. By the compression tests, the 0.2% flow stress at the temperature range from RT to 1073K exceeded 1GPa. The yield stress is comparably higher than those of other E21 intermetallic carbides: at 1073K, 1084MPa for Ti3AlC, 50MPa for Mn3AlC and 135MPa for Fe3AlC. Besides, a weak positive temperature dependence of strength was observed where the peak temperature was around 900K. This suggests that a Kear-Wilsdorf type dislocation pinning mechanism may be activated. It is concluded that E21 Ti3AlC-base alloy shows promise for a new high-temperature light-weight structural material.
Orientation Relationship Between the bcc and σ Phases in Cr-Co Alloys
Authors: Doi Toshihiro , Tanimura Makoto , Koyama Yasumasa 
Published: June 2019

AbstractTo obtain deeper understanding of the Ð structure, the formation of the Ð structure in the (bcc¨bcc+Ð) reaction at 873K and 1173K have been investigated by transmission electron microscopy. As for the orientation relationship between the bcc and Ð structures, as a results, both the common first relation of [110]bcc//[110]Ð and three second relations given by α=0°, 33°, and 64° were found in the 1173K annealing, where α is an angle between the [_110]bcc and [001]Ð directions. In the 873K annealing, on the other hand, there was only one second relation with α=0°. Based on the α=0° relation found in both annealing temperatures, the features of atomic shifts in the Ð-structure formation were also discussed.
Evaluation of the Stability of Raft Structure in Nickel Base Superalloys Throughout their Lifetime
Authors: Tanaka Katsushi , Inoue Toru , Ichitsubo Tetsu , Kishida Kyosuke , Inui Haruyuki 
Published: June 2019

AbstractStability of raft structure in nickel base superalloys has been examined by using elastic energy calculations based on a microelasticity theory. The numerical calculation method for a structurally heterogeneous system is applied. The results indicate that the raft structure is significantly stabilized by introductions of creep deformations till the critical creep deformation at which the lattice misfit between gamma and gamma-prime phases is completely compensated by creep dislocations. When the magnitude of creep deformations exceed the critical value, the (001) lamellar interfaces become elastically unstable and a tilted lamellar interface become the most stable one. This instability of the 001 raft structure leads a tilted or wavy lamellar interfaces for reducing the internal strain energy, that is a precursor to collapse the raft structure.
Irradiation Assisted Grain Boundary Segregation in Steels
Authors: Lu Zheng , Faulkner Roy G 
Published: June 2019

AbstractThe understanding of radiation-induced grain boundary segregation (RIS) has considerably improved over the past decade. New models have been introduced and much effort has been devoted to obtaining comprehensive information on segregation from the literature. Analytical techniques have also improved so that chemical analysis of layers 1 nm thick is almost routine. This invited paper will review the major methods used currently for RIS prediction: namely, Rate Theory, Inverse Kirkendall, and Solute Drag approaches. A summary is made of the available data on phosphorus RIS in reactor pressure vessel (RPV) steels. This will be discussed in the light of the predictions of the various models in an effort to show which models are the most reliable and easy to use for forecasting P segregation behaviour in steels. A consequence of RIS in RPV steels is a radiation induced shift in the ductile to brittle transition temperature (DBTT). It will be shown how it is possible to relate radiation-induced P segregation levels to DBTT shift. Examples of this exercise will be given for RPV steels and for ferritic steels being considered for first wall fusion applications. Cr RIS in high alloy stainless steels and associated irradiation-assisted stress corrosion cracking (IASCC) will be briefly discussed.
The All Boron Carbide Diode Neutron Detector: Experiment and Modeling Approach
Authors: Sabirianov Ildar , Fairchild Robert W , Brand Jennifer I 
Published: June 2019

AbstractBoron carbide diode detectors, fabricated from two different polytypes of semiconducting boron carbide, will detect neutrons in reasonable agreement with theoretical expectations. The performance of the all boron carbide neutron detector differs, as expected, from devices where a boron rich neutron capture layer is distinct from the diode charge collection region (i.e. a conversion layer solid state detector).Diodes were fabricated from natural abundance boron (20% 10B and 80% 11B.) directly on the metal substrates and metal contacts applied to the films as grown. The total boron depth was on the order of 2 microns. This is clearly not a conversion-layer configuration. The diodes were exposed to thermal neutrons generated from a paraffin moderated plutonium-beryllium source in moderated and unmoderated, as well as shielded and unshielded experimental configurations, where the expected energy peaks at at 2.31 MeV and 2.8 MeV were clearly observed, albeit with some incomplete charge collection typical of thinner diode structures. The results are compared with other boron based thin film detectors and literature models.
A Mechanical Study of T91 Embrittlement by Liquid Lead-bismuth Eutectic
Authors: Hamouche Zehoua , AUGER Thierry , GUILLOT Ivan 
Published: June 2019

AbstractThe susceptibility of liquid metal embrittlement of the T91 martensitic steel is investigated from slow deformation rate (6.67x10-8 m.s-1) to high deformation rate (6.67x10-3 m.s-1), using a Center Cracked in Tension geometry. Brittle fracture, characterized by elongated river cracks on all the fracture surfaces, indicates that T91 is sensitive to the Embrittlement by LBE. This embrittlement effect is very marked at the low deformation rate (~10-5 mm.s-1). A ductile-brittle transition is observed in the high strain rate range investigated. In this transition regime, there is a competition between the growth of dimples and the cracking induced by the liquid metal. Ductility recovery is complete at the highest investigated displacement rate. This dependence of T91/LBE susceptibility to LME on the displacement rate and the brittle to ductile transition at high strain rate is confirmed by a fracture mechanics analysis.
Bubble Density Dependent Functionals to Describe Deformation and Stress Equilibrium Evolution for In-Reactor Nuclear Fuel Materials
Authors: Stout Ray B. 
Published: June 2019

AbstractFuture designs of nuclear fuels require an increased understanding of fission gas bubble density evolution. Derivations will be provided for a generic Boltzmann bubble density evolution equation, a bubble density deformation field equation, and a Cauchy stress/bubble-pressure equilibrium equation.
Ordered Arrays of Colloidal Gold Nanoparticles Fabricated by Focused Ion Beam Techniques
Authors: Simpson Todd , Mitchell Ian V 
Published: June 2019

AbstractThrough-holes of diameter 35nm and larger were milled in 100nm thick silicon nitride windows by focused ion beam milling. The holes were sized to optimize capture of gold nanoparticles from a liquid suspension. The colloidal suspensions of gold particles were deposited onto the membrane and drawn through the holes by capillary forces. Efficient, single particle filling is demonstrated for both 100nm and 250nm diameter particles indicating that once a hole is filled, flow can be effectively blocked. We show that lithographically defined arrays of colloidal gold can be achieved with >98% filling.
Direct Focused Ion Beam Drilling of Nanopores
Authors: Patterson Nick , Hodges V. Carter , Vasile Michael J. , Adams David P. , Chen Zhu , Brinker C. Jeff 
Published: June 2019

AbstractFocused 30keV gallium ion beam, single-pixel drilling combined with backside particle detection is used to fabricate pores having exit diameters as small as ~11 nm in 200 nm-thick silicon nitride membranes. The backside channelplate detector response obtained about the onset of breakthrough is interpreted by plan-view transmission electron microscopy investigations of hole morphology. Immediately prior to breakthrough, there is a rise in detector signal as the local membrane thickness is reduced. This likely occurs as a result of ion transmission and, possibly, forward sputtering. At the dose required for breakthrough a maximum detector signal is obtained thus providing a potential method for end point detection. The focused ion drilling technique avoids broad area beam exposure methods that are often used to reduce hole diameter to nanometer dimension. In addition, the current approach overcomes difficulties in determining a required dose for breakthrough such as those that arise from an inhomogeneous membrane thickness, redeposition, or ion channeling.
Fabrication of Sub-250nm High Aspect Ratio Apertures by Focused Ion Beam Lithography
Authors: Simpson Todd , Mitchell Ian V 
Published: June 2019

AbstractAperture arrays were fabricated in 1.0µm thick gold films supported on 20nm thick silicon nitride membranes. Lithographic milling strategies in gold were evaluated through the use of in-situ sectioning and high resolution SEM imaging with the UWO CrossBeam FIB/SEM. A successful strategy for producing a 250nm diameter hole with sidewalls approaching vertical is summarized.
Probe Tip Replacement System Inside the FIB
Authors: Amador Gonzalo , Zaykova-Feldman Lyudmila , Moore Thomas M 
Published: June 2019

AbstractThe in-situ lift-out method for TEM sample preparation, based on the use of a chamber-mounted nanomanipulator and FIB induced material deposition, has proven its effectiveness over the last several years. The time-efficiency introduced by this method is one reason for its success and rapid adoption within the semiconductor industry. Improvements to in-situ TEM lift-out preparation have been pursued to further improve sample processing time. One area targeted has involved methods to enable rapid in-situ probe tip replacement without having to remove the probe shaft from the vacuum chamber. This paper describes an in-situ probe tip replacement system that successfully solves this problem.
Micro-Fracture testing of Ni-W Microbeams Produced by Electrodeposition and FIB Machining
Authors: Armstrong David , Haseeb Abdul , Wilkinson Angus , Roberts Steve 
Published: June 2019

AbstractElectrodeposited nickel-tungsten alloys are being considered as a candidate material for components for microelectromechanical systems (MEMS) fabricated by the LIGA (German acronym for lithography, electrodeposition, and forming) technology. In spite of having a useful range of properties including; hardness and strength, better tribological and chemical resistance and improved high temperature resistance as compared with the conventionally used electrodeposited Ni, these alloys possess certain brittleness. In this study, the fracture toughness of Ni-17.5 at%W alloy microcantilever beams (dimension: 60µm × 20µm x 14µm) fabricated by UV lithography and electrodeposition and notched by focused ion beam machining is investigated. Load was applied to the beams using a nanoindenter, which also allowed accurate positioning of the sample. Fracture toughness was calculated from the fracture load assuming a linear elastic behaviour. The Ni-W alloy beams were found to possess a mean fracture toughness of 2.97 MPa √m. The fracture toughness of Ni-W alloy is found to be higher than that of Si - another important MEMS material, but considerably lower than that of electrodeposited nickel and nickel base alloys.
3D Structure Fabrication by FIB Milling and Deposition
Authors: Fujii Toshiaki , Iwasaki Koji , Munekane Masanao , Yamamoto Yo , Takeuchi Toshitada , Hasuda Masakatsu , Ikku Yutaka , Tashiro Hiromi , Asahata Tatsuya , Kiyohara Masahiro , Kaito Takashi 
Published: June 2019

AbstractFocused Ion Beam (FIB) system is equipment used to make a wide variety of micro and Nano structures. Structures can be created using various materials by irradiating focused gallium ion beam on to the surface of specimens and by sputtering, etching and ion beam induced deposition. In order to realize greater diversity for nano construction by using the FIB system, we have developed technologies incorporating:-	Built-in pattern signal generator-	Multiple Gas Unit for gas assisted etching and beam induced deposition-	A precision wheel for the stage.This latest FIB system has a narrow Ion beam with a diameter of better than 4nm. Beam current is controlled from 0.15pA to 20nA. These performances contribute significantly to the study 3D structures fabrication and modification.
Comparative Photoemission Study of Actinide (Am, Pu, Np and U) Metals, Nitrides, and Hydrides
Authors: Gouder Thomas , Seibert Alice , Rebizant Jean , Huber Frank , Havela Ladislav 
Published: June 2019

AbstractCore-level and valence-band spectra of Pu and the other early actinide compounds show remarkable systematics, which can be understood in the framework of final state screening. We compare the early actinide (U, Np, Pu and Am) metals, nitrides and hydrides and a few other specific compounds (PuSe, PuS, PuCx, PuSix) prepared as thin films by sputter deposition. In choosing these systems, we combine inherent 5f band narrowing, due to 5f orbital contraction throughout the actinide series, with variations of the chemical environment in the compounds. Goal of this work was to learn more on the electronic structure of the early actinide systems and to achieve the correct interpretation of their photoemission spectra. The highly correlated nature of the 5f states in systems, which are on the verge to localization, makes this a challenging task, because of the peculiar interplay between ground state DOS and final-state effects. Their influence can be estimated by doing systematic studies on systems with different (5f) bandwidths. We conclude on the basis of such systematic experiments that final-state effects due to strong e-e correlations in narrow 5f-band systems lead to multiplet like structures, analogous to those observed in the case of systems with localized electron states. Such observations in essentially band-like 5f-systems was first surprising, but the astonishing similarity of photoemission spectra of very different chemical systems (e.g. PuSe, Pu2C3 and δ-Pu) points to a common origin, relating them to atomic features rather than material dependent density of states (DOS) features.
Localized and Itinerant States in Actinide Materials
Authors: Joyce J.J. , Durakiewicz T. , Olson C. G. , Guziewicz E. , Graham K. S. , Moore D. P. , Morales L. A. 
Published: June 2019

AbstractThe electronic structure of single crystal UO2 and polycrystalline δ-Pu is examined using photoelectron spectroscopy. These two actinide materials exhibit properties consistent with the 5f electrons at the threshold between localized and itinerant character. The results for δ-Pu may be viewed as the 5f electrons exhibiting a dual nature with some fraction of the 5f levels localized and not participating in the bonding while the other fraction of 5f character is involved in bonding and hybridization with the conduction electrons. For UO2 where angle-resolved photoemission is available, one observes dispersion in the 5f features indicative of the 5f electrons being influenced by the periodic potential of the lattice rather than purely influenced by the site to which the 5f electrons are generally localized.
Nature of Non-magnetic Strongly-Correlated State in Plutonium
Authors: Purovskii Leniod , Shick Alexander , Havela Ladislav , Katsnelson Mikhail , Lichtenstein Alexander 
Published: June 2019

AbstractLocal density approximation for the electronic structure calculations has been highly successful for non-correlated systems. The LDA scheme quite often failed for strongly correlated materials containing transition metals and rare-earth elements with complicated charge, spin and orbital ordering. Dynamical mean field theory in combination with the first-principle scheme (LDA+DMFT) can be a starting point to go beyond static density functional approximation and include effects of charge, spin and orbital fluctuations. Ab-initio relativistic dynamical mean-field theory is applied to resolve the long-standing controversy between theory and experiment in the “simple” face-centered cubic phase of plutonium called δ-Pu. In agreement with experiment, neither static nor dynamical magnetic moments are predicted. In addition, the quasiparticle density of states reproduces not only the peak close to the Fermi level, which explains the large coefficient of electronic specific heat, but also main 5f features observed in photoelectron spectroscopy.
Comparative Experimental Study of X-Ray Absorption Spectroscopy and Electron Energy Loss Spectroscopy on Passivated U Surfaces
Authors: Nelson Art J. , Moberlychan W. J. , Bliss R. A. , Siekhaus W. J. , Felter T. E. , Denlinger J. D. 
Published: June 2019

AbstractX-ray absorption spectroscopy and electron energy loss spectroscopy are complementary analytical techniques on energy and spatial resolution. These techniques are based on the same fundamental physical process of core excitation with either an incident photon or incident electron. In the proper experimental configuration the electron and photon inelastic scattering amplitudes are comparable and thus the x-ray and electron absorption edges look identical. We have applied these two complementary analytical techniques to investigate the electronic structure of C ion implanted U. Implantation of C+ ions into U238 has been shown to produce a physically and chemically modified surface layer that passivates the surface preventing further air oxidation and corrosion. Comparison of the resultant spectra reveal that transitions between the initial state and a series of final states yield numerous strong features at the absorption edge that can provide structural information and information on the local chemical environment, including the character of the U 5f state.
Radiation Damage Effects on the Magnetic Properties of Pu(1-x)Amx (x=0.224)
Authors: McCall Scott K. , Fluss M. J. , Chung B. W. , McElfresh M. W. , Haire R. G. 
Published: June 2019

AbstractPu(Am) is stable in the fcc δ-phase from a few atomic percent to nearly 80 atomic percent Am, expanding the average interatomic separation as the alloy concentration of Am increases. Both Pu and Am spontaneously decay by α-emission creating self-damage in the lattice in the form of vacancy-interstitial pairs and their aggregates. At sufficiently low temperatures, the damage is frozen in place, but can be removed by thermal annealing at sufficiently high temperatures, effectively resetting the system to an undamaged condition. The magnetic susceptibility and magnetization are observed to increase systematically as a function of accumulated damage in the fcc δ-Pu(1-x)Am(x) (x=0.224). Some results of these observations are reported here.
Physical Property Changes in Plutonium Observed from Accelerated Aging using Pu-238 Enrichment
Authors: Chung Brandon W. , Choi Bill , Saw Cheng , Thompson Stephen , Woods Conrad , Hopkins David , Ebbinghaus Bartley 
Published: June 2019

AbstractWe present changes in volume, immersion density, and tensile property observed from accelerated aged plutonium alloys. Accelerated alloys (or spiked alloys) are plutonium alloys enriched with approximately 7.5 weight percent of the faster-decaying 238Pu to accelerate the aging process by approximately 17 times the rate of unaged weapons-grade plutonium. After sixty equivalent years of aging on spiked alloys, the dilatometry shows the samples at 35°C have swelled in volume by 0.15 to 0.17 % and now exhibit a near linear volume increase due to helium in-growth. The immersion density of spiked alloys shows decrease in density, similar normalized volumetric changes (expansion) for spiked alloys. Tensile tests show increasing yield and engineering ultimate strength as spiked alloys are aged.
Uranium Hydride Formation Study as Observed by Scanning Surface Potential Imaging
Authors: Hawley Marilyn E. , Hill Mary Ann , Wang Yongqiang , Schulze Roland K. 
Published: June 2019

AbstractUranium is an extremely important material for commercial and military applications (i.e. nuclear power, nuclear weapons, conventional weapons, and armor systems) and, like a number of other materials, is vulnerable to corrosion by environmental gases that affect their properties, leading to component degradation, shortened lifetimes and materials failure. For uranium this is particularly true in the case of corrosion by hydrogen. A fundamental understanding of the corrosion process at the nucleation stage is of critical importance. The goal of this work is to study the role of common chemical impurities in uranium with initiation sites for the formation of destructive hydride blisters. Samples were implanted with various ions, annealed under vacuum at 200°C, than exposed to one atm of ultra-pure hydrogen. Scanning force microscopy surface potential imaging was used to characterize the structure and corresponding electrical properties of polycrystalline uranium surfaces that resulted from the implantation of different suspect atoms after exposure to hydrogen gas. Surface potential images revealed features related to different oxide structures and hydride spots/blisters as well as other features not obvious in the corresponding topograph. In the surface potential images, blisters appear as bright (higher potential) features in sharp contrast to the uranium oxide background. Often a possible inclusion was observed in the center of a blister. Blister formation did not appear to correlate with implantation of any specific specie, however, distinct differences were seen between implanted and non implanted sides of the same sample.
Effects of Long-Term Service on The Aging Behavior of A Water-Quenched U6Nb Alloy
Authors: Zhou Jikou , Hsiung Luke L. 
Published: June 2019

AbstractMicrohardness testing and transmission electron microscopy are used to study the effects of long-term service on the aging behavior of a water-quenched U-6wt.% Nb alloy when subjected to isothermal aging at 200°XC. The original α''c phase in the WQ-U6Nb alloy is found to become partially ordered over 18 years of aging at ambient temperatures, i.e., natural aging, forming a microstructure that is featured by antiphase domain boundaries (APBs). When subsequently aged at 200 °C, an ordered phase U3Nb is precipitated through a nucleation-and-growth mechanism, suppressing spinodal decomposition that occurs when the water-quenched alloy is artificially aged at the same temperature. The different phase transformation paths lead to different microhardness changes during artificial aging: the naturally aged alloy is more slowly hardened, but to a greater microhardness peak value.