bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Multi-Plane Model for Defect Nucleation at Cracks
Authors: Beltz G. E. , Schmauder S. 
Published: March 2011

AbstractA mathematical model (2D) of dislocation generation at cracks on interfaces is presented, which takes into account the role of slip processes on several slip planes in the vicinity of a crack. The work investigates the effects of other incipient dislocations on the nucleation and emission of the primary dislocation that emits first and is responsible for crack-tip blunting on atomic length scales. The modeling makes use of the recently-developed Peierls-Nabarro framework for dislocation nucleation. It is found that there is a moderate increase in the critical load necessary to emit a dislocation, when incipient slip activity is allowed to occur on the prolongation of the crack plane. Furthermore, the slip at the tip, the quantity which characterizes to what extent an incipient dislocation forms before it emits, decreases when the dual slip-plane model is used. Implications for the ductile versus brittle response of Ni are discussed.
Migration Dynamics of a Σ=3 {112} Boundary in Aluminum
Authors: Medlin D.L. , Stobbs W.M. , Weinberg J.D. , Angelo J.E. , Daw M.S. , Mills M.J. 
Published: March 2011

AbstractWe present a study of the structure and migration mechanisms of the Σ=3 {112} boundary in aluminum. Measurements of the static boundary, using both High Resolution Transmission Electron Microscopy (HRTEM) and the α-fringe technique, are consistent with the lowest energy boundary structure that is predicted by the Embedded Atom Method (EAM). HRTEM observations of the migrating boundary are also presented. The boundary is mobile and upon translation produces coherent {111} twin boundary steps. The atomistic processes that are involved in this migration are considered in terms of the required twinning shears and the results of molecular dynamics simulations using the EAM. The initial nucleation of steps in the boundary appears to be electron beam induced.
Interactions of Dislocations and Deformation Twins with Interfacial Boundaries in Titanium Aluminides
Authors: Appel Fritz , Wagner Richard 
Published: March 2011

AbstractThe deformation behaviour of two-phase titanium aluminide alloys with a lamellar microstructure of the intermetallic phases α2(Ti3Al) and y(TiAl) was studied. The interaction processes of dislocations and deformation twins, respectively, with the lamellar interfaces are investigated by conventional and high-resolution electron microscopy. The mechanisms of translation of shear deformation across, the lamellar boundaries depend on their structure. Semicoherent interfaces are very effective barriers limiting the propagation of shear deformation. The misfit dislocations present at these interfaces support, on the other hand, the generation of dislocations and deformation twins. The observed processes are discussed regarding plastic deformation and crack propagation in the material.
Structural Evolution and Deformation in an Aluminum-Based Solid Solution Alloy with Submicron Grain Size
Authors: Wang Jingtao , Horita Zenji , Nemoto Minoru , Furukawa Minoru , Valiev Ruslan Z. , Ma Yan , Langdon Terence G. 
Published: March 2011

AbstractSuperplastic ductilities may be achieved in tension using polycrystalline materials with small grain sizes (typically <10 μm). Experiments were conducted to evaluate the significance of the grain boundaries in an Al-3% Mg solid solution alloy with a submicron grain size (∼0.2 μm). The material was produced by subjecting the alloy to severe plastic strain using a pressing technique. This paper describes the nature of the microstructure in the as-fabricated condition, the evolution of the microstructure as a function of time and/or temperature, and the effect of testing in tension at a temperature of 403 K.
Experimental Measurement of the Local Electronic Structure of Grain Boundaries in Ni3Al
Authors: Muller D.A. , Batson P.E. , Subramanian S. , Sass S. L. , Silcox J. 
Published: March 2011

AbstractWe have examined grain boundaries in both undoped and boron doped Ni0.76Al0.24using electron energy loss spectroscopy (EELS), x-ray fluorescence (EDX) and annular dark field (ADF) imaging in a UHV STEM. A detailed study of a high angle grain boundary in nickel rich Ni3Al doped with 1000 ppm boron shows nickel enrichment occurring in a 5Å wide region. Boron segregation to the boundary is observed with EELS and is seen to vary along the boundary, coinciding with ADF contrast changes in the surrounding grains that may be due to local strain fields. Spatially resolved EELS of the Ni L2,3core edge, which is sensitive to changes in the hole density in the nickel d band, shows boron rich regions of the grain boundary to have a bonding similar to that of the bulk material. Boundary regions without boron have an electronic structure similar to that of the undoped grain boundaries where the Fermi level lies deeper in the nickel d band. In addition to studying boron segregation, EELS provides a unique opportunity to examine the changes in bonding that control the local properties of the material.
Nearly Dislocation-Free APB Termination at Pure Grain Boundary Step Defects in L10 Alloys
Authors: Singh Abha , King A.H. 
Published: March 2011

AbstractL10 alloys typically derive from a high-temperature, disordered fcc phase. For example, CuAu has a face centered tetragonal structure below 380°C and is derived from its high temperature, disordered face centered cubic phase. As the material transforms from the disordered fcc phase to the ordered tetragonal phase, the four distinct Σ3 fcc twin misorientations generate twelve distinct tetragonal twin misorientations, four being characterized as Σ3 and eight as Σ6. Of particular interest is the Σ6 structure because it is possible to terminate lattice antiphase boundaries without dislocations at this interface. A pure step defect at the interface can accommodate the APB termination due to anti-site coincidence (coincidence between copper and gold sites). We term these defects “antiphase steps”. The antiphase step is a new type of interfacial defect that has not been described by other workers. The possibility of forming antiphase steps in ordered L10 alloys is related to even-Σ interfaces. Since the Σ6 boundary is common in the ordered phase, the formation of dislocation-free APB terminations may be important in L10 alloys.
Hrem Observations, Peels Analysis and Numerical Simulations of Au/Ni Mbe Multilayers
Authors: Bayle Pascale , Deutsch T. , Gilles B. , LancÇn F. , Marty A. , Thibault J. , Colliex C. , Tence M. 
Published: March 2011

AbstractThe structural evolution of Au/Ni multilayers (with an increasing number of Ni monolayers (MLs)) has been investigated by HREM. As soon as the thickness of Ni becomes larger than 5 MLs, a structural change occurs which in fact has been predicted by numerical simulations. The deformation in the multilayer has been characterised by HREM image processing and has been related to the Ni profile. This profile has been compared to the chemical profile obtained by scanning PEELS analysis through the multilayer.
Localized Influence of Solute on the Stacking Fault Energy of Dilute Al-Based Solid Solutions
Authors: Rohrer C. Lane 
Published: March 2011

AbstractThe stacking fault energy (SFE) is widely used to classify the mechanical behavior of pure metals. In alloys, however, the experimentally observed SFE is strongly influenced by localized solute effects. To further understand these effects on dislocation structure and on the observed SFE, solute segregation to an extended edge dislocation dipole, delineating two stacking faults, was studied in dilute Al:Cu, Al:Ag, and Al:Cu, Ag solid solutions. Cu and Ag were chosen to isolate solute size and modulus effects, Cu being smaller than Al, while Ag and Al are essentially the same size. Atomistic Monte Carlo results showed little change in the partial dislocation spacing in the binary systems as compared to the spacing in pure Al, even though Cu was observed to segregate to the compressive regions of the dislocation dipoles, forming widespread atmospheres, while Ag formed randomly distributed Ag-rich zones. However, in ternary Al:Cu,Ag simulations, the Ag apparently inhibited the Cu from distributing across the width of the extended dislocations, both Ag and Cu forming small clusters near or on the partial dislocations which increased the partial dislocation spacing. Results will be discussed in light of interpretations of experimental SFE determinations, emphasizing the importance of the localized solute distribution on the SFE.
Effect of Boron and Hydrogen on the Electronic Structure of Ni3Al
Authors: Kioussis N. , Watanabe H. , Hemker R.G. , Gourdin W. , Gonis A. , Johnson P.E. 
Published: March 2011

AbstractUsing first-principles electronic structure calculations based on the Linear-Muffin-Tin Orbital (LMTO) method, we have investigated the effects of interstitial boron and hydrogen on the electronic structure of the L12 ordered intermetallic Ni3A1. When it occupies an octahedral interstitial site entirely coordinated by six Ni atoms, we find that boron enhances the charge distribution found in the strongly-bound “pure” Ni3AI crystal: Charge is depleted at Ni and Al sites and enhanced in interstitial region. Substitution of Al atoms for two of the Ni atoms coordinating the boron, however, reduces the interstitial charge density between certain atomic planes. In contrast to boron, hydrogen appears to deplete the interstitial charge, even when fully coordinated by Ni atoms. We suggest that these results are broadly consistent with the notion of boron as a cohesion enhancer and hydrogen as an embrittler.
Effect of Molybdenum on the Electronic Structure of Iron Grain Boundaries with Phosphorus and Boron
Authors: Krasko Genrich L. 
Published: March 2011

AbstractWe are reporting preliminary results on LMTO supercell calculations on a Σ3 (111) grain boundary (GB) in Fe with Mo atoms sitting at the GB plane. Calculations were performed both for the clean (CL) GB and GB with P/B atoms occupying centers of host (Fe and Mo) atom trigonal prisms (a coordination typical of the Fe GBs). The geometry of the GBs was not changed upon substituting Mo for Fe in the GB plane: all the interplanar distances and atomic radii were preserved (these were calculated earlier for the Fe GBs from GB3 relaxation modelling using the Embedded Atom Method). Comparison of the electron charge-density distributions within the atomic spheres for GBs with and without Mo, has shown that the presence of Mo at the GB plane increases both the number of d-electrons and the total charge density within atomic spheres of the atoms most important for intergranular cohesion. This should result in enhanced cohesion. The magnetic moments of the constituent atoms were also found to be strongly affected by the addition of Mo. The Mo atoms are anti-ferromagnetically coupled with the neighboring Fe atoms: mM0=-O.6OμB (CL GB), mMo=-O.14μB (GB with P), and mMo=-O.18μB (GB with B).
Molecular Statics of a Ni/Zr Heterophase Interface
Authors: Fernandes M. G. , Pontikis V. , Bristowe P.D. 
Published: March 2011

AbstractAn atomistic model for a Ni/Zr hetero-interface formed between closed packed atomic planes is constructed and simulated using energy minimization techniques. The results show how misfit dislocations are introduced in the system and form an hexagonal array, and that the strain field in Ni can reach values two times larger than those in Zr. Calculated values for antisite defect energies are positive and are a strong function of position at the interface, reflecting the role of the dislocation network.
Boron and Hydrogen in NI3AL: Part II. Mechanical Testing of Bicrystals
Authors: Johnson Patricia E. , Gourdin W. , Gonis A. , Kioussis N. , Vaudin M. 
Published: March 2011

AbstractTo provide a sensitive measurement of the effect of boron segregation on the strength and ductility of Ni3A1 grain boundaries, bicrystal tensile tests were performed on small specimens of boron doped Ni76A124 cut from extremely large-grained boules. Five specimens with the same “random” or low-symmetry grain boundary (disorientations measured by means of backscattered Kikuchi patterns) and two specimens with a second random grain boundary were tested in quenched and slow-cooled conditions. Duplicate tests performed in a low (7 ppm) water-vapor environment showed that the fracture mode and the stress and strain at fracture are altered by environmental embrittlement at individual, partially strengthened grain boundaries.
Defect-Solute Interactions Near Irradiated Grain Boundaries
Authors: Simonen E. P. , Vetrano J. S. , Heinisch H. L. , Bruemmer S. M. 
Published: March 2011

AbstractDefect-solute interactions control radiation-induced segregation (RIS) to interfacial sinks, such as grain boundaries, in metallic materials. The best studied system in this regard has been austenitic stainless steels. Measurements of grain boundary composition indicate that RIS of major alloying elements is in reasonable agreement with inverse-Kirkendall predictions. The steep and narrow composition profiles are shown to result from limited back diffusion near the boundary. Subsequently, defect-solute interactions that affect the near-boundary defect concentrations strongly affect RIS. The variability in measured RIS may in part be caused by grain boundary characteristics.
Bias Annealing Effect on Hydrogen-Containing Au/N-Silicon Schottky Barrier
Authors: Yuan M.H. , Jia Y.Q. , Qin G.G. 
Published: March 2011

AbstractAu/n-Si Schottky barrier (SB) incorporated by hydrogen has a 0.13 eV lower SB height (SBH) than that without hydrogen incorporation. For the hydrogen-containing SB, zero bias annealing (ZBA) decreases the SBH while reverse bias annealing (RBA) increases it. Besides, the ZBA and RBA cycling experiments reveal a reversible change of the SBH with in at least three cycles. The higher annealing temperature of RBA results in higher SBH. We interpret the above experimental facts as that hydrogen has an effect on metal-semiconductor interface states and then on the SBH, and both the bias on SB and temperature of annealing can influence the hydrogen effects on metal-semiconductor interface states.
The Nature of Oxygen-Related Polytypoids in the Aluminum Nitride-Aluminum Oxide System
Authors: Youngman R.A. 
Published: March 2011

AbstractPrevious investigations into the nature of polytypoid structures in the A1N-A12O3 and A1NSiO2 systems have concluded that these structures are comprised of ordered stacking faults which accommodate oxygen (and silicon) in the basic wurtzite (2H) AIN structure. The polytypoids are distinct chemical phases intimately related to the pure 2H AIN. More recent work in low oxygen content (<6 at.%) A1N has elucidated the evolution of oxygen-related point defects, and transformation of these defects into extended structures. These studies have shown that all oxygenrelated extended defects in the A1N-A12O3 system are inversion domain boundaries (IDBs).We present here extensions of the concepts developed from low oxygen content studies which lead to direct application in understanding the polytypoid structures. High resolution electron microscopy (HREM), specific electron diffraction experiments, and structural models are utilized to prove that the polytypoid structures are not based on stacking faults, but, in fact are based on IDBs.
An Investigation on Interconnect Via Failure
Authors: Zhao Joe W. , Doherty John , Whitefield Bruce 
Published: March 2011

AbstractThe formations of insulating material and voids at the interface between metal 1 and metal 2 in interconnect vias in Al-1%Si-0.25Cu% alloy has been investigated. A thin layer between metal 1 and 2 interface was identified using Transmission Electron Microscopy(TEM). The material was analyzed using TEM with Energy Dispersive X-ray spectroscopy(EDX) confirming that the insulating layer was Silicon. It is believed that the via failure was due to the formation of silicon precipitate at the interface and the coalescence of voids after High Temperature Storage(HTS) test for a long time period. The formation of Si precipitate and the growth of voids at the interface of aluminum alloy in interconnect via is dependent on the grain structure. The formation of voids at via interface is related to thermal treatment position in backend process. A change of thermal treatment position has been made, and no via failure has been found after HTS test for 2000 hours. A model is proposed for the mechanism of the via open failure.
Interfaces in Silicon Carbide Whisker and Carbon Fiber Reinforced Calcium Phosphate Composites
Authors: Park K. , Sung C. , Sundaresan S. , Vasilos T. 
Published: March 2011

AbstractThe microstructural and chemical characteristics of silicon carbide whisker/calcium phosphate and carbon fiber/calcium phosphate composites were studied using analytical transmission electron microscopy. The interface at these calcium phosphate-based composites was studied, with particular attention to finding evidence of a chemical reaction at the interface. Structural observations made on these composites explain the fact that their mechanical properties may be strongly affected by the structural properties.
The use of thin Film Substrates to Study Enhanced Solid-State Phase Transformations
Authors: Kotula PAUL G. , Erickson Dwight D. , Carter C. Barry 
Published: March 2011

AbstractA thin-film substrate geometry is described for the study of enhanced or seeded solid-state phase transformations. As an example of this approach, thin films of hematite have been used as substrates for the study of the seeded phase transformation of a boehmite-derived transition-alumina to α-A12O3. The hematite films were grown on bulk (0001) α-A12O3 single crystal substrates by pulsed-laser ablation. A layer of a boehmite sol was then spin-coated onto the thin film. The assemblages were then heated to 950°C, or 1000°C in order to induce the phase transformation. Specimens were imaged in cross section by transmission electron microscopy. No transformation was observed for specimens heated to 950°C. In specimens heated to 1000°C, the transition alumina was found to transform to alpha-alumina, starting at the surface of the hematite film, via solid-state heteroepitaxy. In this case, islands, growing out from the hematite film into the transition alumina layer, were observed.
Observation of the Phase-Boundary Controlled Formation of NiA12O4 From a Single-Crystal NiO Thin Film and a Single-Crystal α-A12O3 Substrate
Authors: Kotula Paul G. , Carter C. Barry 
Published: March 2011

AbstractHigh-quality NiO thin films have been grown on single-crystal α-A12O3 substrates ((0001) orientation) by pulsed-laser ablation, forming essentially the idealized solid-state reaction geometry-a single-crystal film in intimate contact with a single-crystal substrate. These reaction couples have been characterized by cross-section transmission electron microscopy and scanning electron microscopy both before and after being heated in air to induce the solid-state reaction (i.e., Ni-spinel formation). The NiO films consisted of two twin variants which were found to conform to the underlying substrate surface steps. The substrate surface steps were produced by heat-treating the substrates prior to thin film deposition. Using this reaction geometry, it has been found that the initial reaction of the spinel takes place where twin boundaries in the NiO films meet the substrate. The initial reaction corresponds to the nucleation of the spinel. This interpretation is supported by the fact that the reaction proceeded faster up the NiO twin boundaries than elsewhere along the reaction layer (i.e., nucleation of the spinel is easier at twin boundaries in the NiO film). Scanning electron microscopy has been used with the present thin-film reaction geometry to measure reaction layer width along interfaces up to 2 mm long.
Tem Analysis of Interfacial Reactions Between TiWn, Wn Gate Metallizations and GaAs in Mesfet Devices
Authors: Jones K.S. , Robinson H.G. , Jasper C. , Cronin W. , Durlam M. 
Published: March 2011

AbstractIn an effort to improve the uniformity of the threshold voltage, the Schottky barrier height, and the ideality factor, Ti0.29W0.52N0.19 and W0.81N0.19 gate metal depositions have been investigated as a function of annealing conditions for GaAs based MESFET devices. Crosssectional TEM samples were made of each device. The results of these studies indicate there is a systematic and significant reaction occurring between the gate metal and the GaAs upon 850°C and 900°C rapid thermal annealing. These reactions take different forms depending on whether Ti is present or not. If Ti is absent (i.e. WN gates) then the interfacial roughness between the gate and the GaAs is less than 30Å indicating the metallization is very unreactive. The WN contacts for some gates show void formation indicative of GaAs decomposition also for some devices an amorphous layer is observed at the interface. Selected area diffraction patterns indicate only the alpha-W and beta-W2N phases are present. For the TiWN gates the interface roughness is as large as 200Å upon 900°C 10 second RTA. However no voids or interfacial amorphous layers were observed. Again only alpha-W and beta-W2N were observed in the bulk of the gates. For both systems, beta-W2N appears to form at the interface however the morphology of the beta-W2N grains are much larger for the TiWN gates. Electrical results indicate the TiWN gates have a lower ideality factor (near 1.1) and greater uniformity across the wafer compared to the WN gates. It is proposed that the presence of Ti in the gate metal aids in reducing any surface oxides thus improving the ideality and uniformity of the gate metal/GaAs contact.
Waste Glass Corrosion Modeling: Comparison with Experimental Results
Authors: Bourcier William. L. 
Published: March 2011

ABSTRACTModels for borosilicate glass dissolution must account for the processes of (1) kinetically-controlled network dissolution, (2) precipitation of secondary phases, (3) ion exchange, (4) rate-limiting diffusive transport of silica through a hydrous surface reaction layer, and (5) specific glass surface interactions with dissolved cations and anions. Current long-term corrosion models for borosilicate glass employ a rate equation consistent with transition state theory embodied in a geochemical reaction-path modeling program that calculates aqueous phase speciation and mineral precipitation/dissolution. These models are currently under development. Future experimental and modeling work to better quantify the rate-controlling processes and validate these models are necessary before the models can be used in repository performance assessment calculations.
Science and Licensing: Let's Get off the Collision Course
Authors: Van Konynenburg R. A. 
Published: March 2011

ABSTRACTThe best possibility for gaining an understanding of the likely future behavior of a high level nuclear waste disposal system is use of the scientific method. However, the scientific approach has inherent limitations when it comes to making long-term predictions with confidence. This paper examines these limiting factors as well as the criteria for admissibility of scientific evidence in the legal arena, and concludes that the prospects are doubtful for successful licensing of a potential repository under the regulations that were binding until recently. Suggestions are made for remedying this situation.
Demonstration of Safety for Geologic Disposal
Authors: Taylor Edward C. , Ramspott Lawrence D. , Sprecher William M. 
Published: March 2011

ABSTRACTThe U. S. Department of Energy (DOE) is developing a nuclear waste management system that will accept high-level radioactive waste, transport it, store it, and ultimately emplace it in a deep geologic repository. The key activity now is determining whether Yucca Mountain, Nevada is suitable as a site for the repository. If so, the crucial technological advance will be the demonstration that disposal of nuclear waste will be safe for thousands of years after closure. This paper assesses the impact of regulatory developments, legal developments, and scientific developments on such a demonstration.