bluuebunny/crossref_metadata_2025_split huggingface dataset:
Point Defects Observed in D-T neutron irradiated Copper, Silver and Gold at 288 K with a Rotating Target in FNS_JAERI
Authors: Shimomura Y. , Sugio K. , Ohkubo H. , Mukouda I. , Kutsukake C. , Takeuchi H. 
Published: April 2011

ABSTRACTA 14 MeV D-T(fusion) neutron irradiation was carried out at fusion neutron source facility (FNS) in Japan Atomic Energy Research Institute (JAERI). Specimen temperature was controlled to 288 K. Fluence was 6.1 × 1017to 1.1 × 1021 n/m2. Both TEM thin foil and bulk specimens were irradiated at the same position. At 1018 n/m2, defects observed were single isolated dot defects. With increasing fluence, dot defects changed to complicate structure and made groupings. In a dot group, interstitial clusters and vacancy clusters were observed together. The present result was explained by the modeling that point defects in a nascent damage cascade move in crystal at 288 K and form their defect groupings.
Ion-Irradiation-Induced Amorphization Of Cadmium Niobate Pyrochlore
Authors: Meldrum A. , Beaty K. , Boatner L. A. , White C. W. 
Published: April 2011

ABSTRACTIrradiation-induced amorphization of Cd2Nb2O7 pyrochlore was investigated by means of in-situ temperature-dependent ion-irradiation experiments in a transmission electron microscope, combined with ex-situ ion-implantation (at ambient temperature) and RBS/channeling analysis. The in-situ experiments were performed using Ne or Xe ions with energies of 280 and 1200 keV, respectively. For the bulk implantation experiments, the incident ion energies were 70 keV (Ne+) and 320 keV (Xe2+). The critical amorphization temperature for Cd2Nb2O7 is ∼480 K (280 keV Ne+) or ∼620 K (1200 keV Xe2+). The dose for in-situ amorphization at room temperature is 0.22 dpa for Xe2+, but is 0.65 dpa for Ne+ irradiation. Both types of experiments suggest a cascade overlap mechanism of amorphization. The results were analyzed in light of available models for the crystalline-to-amorphous transformation and were compared to previous ionirradiation experiments on other pyrochlore compositions.
Modelling of Copper Precipitation in Fe-Cu Alloys Under Irradiation
Authors: Barashev Alexander V. , Golubov Stanislav I. , Bacon David J. 
Published: April 2011

ABSTRACTPrecipitation of copper-rich clusters is a major cause of in-service hardening of reactor pressure vessel steels and has attracted much attention. Experimental studies of microstructural changes in alloys under various conditions have revealed similarities and differences. It has been established that under ageing the precipitate ensemble experiences normal nucleation, growth and Ostwald ripening, a distinguishing feature of which is the bcc-9R-3R-fcc transformations the precipitates undergo during growth. The main effect of electron irradiation is believed to be enhancement of the diffusion of copper and hence acceleration of the kinetics. In the case of neutron irradiation, however, there are many aspects that are not clear. One is that at temperatures less than about 300°C the precipitate size is observed to be very small (∼1-3 nm), i.e. the coarsening rate is very low. In this paper we study this phenomenon by computer simulations based on the “mean-field” approach for describing microstructural evolution.
Doping of GaN by ion implantation
Authors: Alves Eduardo J. , Liu C. , da Silva Maria F. , Soares José C. , Correia Rosário , Monteiro Teresa 
Published: April 2011

ABSTRACTIn this work we report the structural and optical properties of ion implanted GaN. Potential acceptors such as Ca and Er were used as dopants. Ion implantation was carried out with the substrate at room temperature and 550 °C, respectively. The lattice site location of the dopants was studied by Rutherford backscattering/channeling combined with particle induced X-ray emission. Angular scans along both [0001] and [1011] directions show that 50% of the Er ions implanted at 550 oC occupy substitutional or near substitutional Ga sites after annealing. For Ca we found only a fraction of 30% located in displaced Ga sites along the [0001] direction. The optical properties of the ion implanted GaN films have been studied by photoluminescence measurements. Er- related luminescence near 1.54 μm is observed under below band gap excitation at liquid helium temperature. The spectra of the annealed samples consist of multiline structures with the sharpest lines found in GaN until now. The green and red emissions were also observed in the Er doped samples after annealing.
The Effect of Interfacial Free Energies on the Stability of Microlaminates
Authors: Lewis A. C. , Mann A. B. , van Heerden D. , Josell D. , Weihs T. P. 
Published: April 2011

ABSTRACTLaminated composites with polycrystalline layers typically break down at high temperatures through grain boundary grooving and the pinch-off of individual layers. Such materials, when exposed to high temperatures, develop grooves where grain boundaries meet the interfaces between layers. The depths of the grooves are controlled by the ratios of grain boundary and interfacial free energies, γgb/γint. Depending on the dimensions of the grains, these grooves can extend through the entire layer, causing pinch-off at the grain boundary. This pinch-off destroys the layering and eventually leads to a gross coarsening of the microstructure. Because microstructural stability is critical to performance for most applications, the ability to understand and predict the stability of microlaminates is a necessary tool. An existing model of this capillarity-driven breakdown requires the interfacial free energies, γgb and γint, as input parameters. Both biaxial and uniaxial zero creep tests have been used in conjunction with transmission electron microscopy to measure these interfacial energies in Ag/Ni and Nb/Nb5Si3 microlaminates.
An Approach to the Mesoscale Simulation of Grain Growth
Authors: Kinderlehrer David , Livshits Irene , Manolache Florin , Rollett Anthony D. , Ta'asan Shlomo 
Published: April 2011

ABSTRACTThe simulation of curvature driven growth in grain boundary systems is becoming an important tool in understanding the behavior of microstructure evolution and there is much distinguished work in this subject. Here we address the mesoscale simulation of large systems of grain boundaries subject to the Mullins equation of curvature driven growth with the Herring force balance equation imposed at triple junctions. We discuss several novel features of our approach which we anticipate will render it a flexible, scalable, and robust tool to aid in microstructural prediction. What is the result of the simulation? We discuss what such a simulation is capable of predicting, taking as a prototype the histogram of relative area population as it changes through the simulation. We do not use this data to seek the best distribution, like Hillert, Rayleigh, or lognormal. Instead we treat the set of distributions as the solution of an inverse problem for a time varying function and determine the equation they satisfy. This results in a coarse graining of the complex simulation to simpler system governed by a Fokker-Planck Equation. Even so, fundamental questions concerning the predictability of simulations of large metastable systems arise from these considerations.
Nanometer Scale Study of Segregation at Heterophase Interfaces of Molybdenum Nitride Precipitates in an α-Iron Matrix
Authors: Isheim Dieter , Csencsits Roseann , Seidman David N. 
Published: April 2011

ABSTRACTWe are studying heterophase interfaces between molybdenum nitride precipitates and an α-iron matrix on a nanometer scale by electron and atom-probe field-ion microscopies. Fe-2 at.% Mo-0.5 at.% Sn and Fe-2 at.% Mo-0.4 at.% Sb are internally nitrided by annealing in an NH3/2 atmosphere. Nitridation at 550°C produces coherent thin platelet-shaped molybdenum nitride precipitates, while at 600°C semicoherent coarse plates and spheres also form. Segrega-tion of Sn and Sb is observed at the heterophase interfaces of only the semicoherent precipitates. The loss of coherency, that is the formation of misfit dislocations, is essential for substantial interfacial solute segregation to occur at heterophase interfaces.
Dislocation - Grain Boundary Interaction in Nickel Bicrystals Evolution of the Resulting Defects under Thermal Treatment
Authors: Priester Louisette , Poulat Sophie , Décamps Brigitte , Thibault Jany 
Published: April 2011

ABSTRACTThe interactions between lattice dislocations and grain boundaries were studied in nickel bicrystals. Three types of grain boundaries, according to their energy, were investigated : singular σ3 {111}, vicinal near σ11 {311} and general near σ11 {332} grain boundaries. The experiments were performed by transmission electron microscopy using a set of techniques : conventional, weak beam, in situ and high resolution transmission electron microscopy. Dislocation transmission from one crystal to the other was only observed for σ3 {111} GB. It consists in a decomposition within the grain boundary of the trapped lattice dislocation followed by the emission of one partial in the neighbouring crystal. A high resolved shear stress is required to promote the emission process. Most often, the absorbed lattice dislocations or extrinsic grain boundary dislocations react with the intrinsic dislocation network giving rise to complex configurations. The evolutions with time and upon thermal treatment of these configurations were followed by in situ transmission electron microscopy. The evolution processes, which differ with the type of grain boundaries, were analyzed by comparison with the existing models for extrinsic grain boundary dislocation accommodation. They were tentatively interpretated on the basis of the grain boundary atomic structures and defects obtained by high resolution transmission electron microscopy studies.
Dislocation Dynamics in Intermetallic and Oxide Dispersion Strengthened (ODS) Alloys
Authors: Messerschmidta Ulrich , Gudera Susanne , Häusslera Dietrich , Bartscha Martin 
Published: April 2011

ABSTRACTIn situ straining experiments in a high-voltage electron microscope allow the observation of the dynamic behaviour of individual dislocations. Such experiments have been performed on the intermetallic alloys NiAl, NiAl containing 0.2 at% Ta, α-TiAl, and MoSi2, and the oxide dispersion strengthened (ODS) alloys INCOLOY MA956 and INCONEL MA754 in a wide range of temperatures. There are many similarities in the dynamic behaviour of dislocations in the different materials. In the intermetallic alloys, a transition occurs between low temperature mechanisms and a viscous motion in the temperature range of the flow stress anomaly. The viscous motion at high temperatures can be explained by diffusion processes in the dislocation cores, whichcan be described by the theory of the Cottrell effect. The diffusing species can be quite different, alloying components or intrinsic point defects like vacancies and antisite defects existing in the lattice or only in the dislocation cores. If the dislocations are straight and crystallographically oriented during their motion, they may be dissociated and move by a succession of glide and conservative climb between the partial dislocations. In the ODS alloys, the dislocations move between the oxide particles again in a viscous way. The relation between the dislocation dynamics and the strain rate sensitivity of the flow stress is discussed for thedifferent materials.
A New Continuum Scalar Model of Facets
Authors: Xin Tinghui , Wong Harris 
Published: April 2011

ABSTRACTFacets or planar surfaces appear often on crystalline solids, and need to be accurately modeled in studying surface evolution. Here we propose a model in which the radius of curvature of the equilibrium crystal surface is prescribed as a function of crystallographic orientation. In this approach, a facet is represented by the Dirac delta function with the weight of the delta function equal to the width of the facet plane. This model allows sharp corners on solid surfaces, but avoids the non-uniqueness of equilibrium surface profiles that plagues previous facet models. We demonstrate this approach by solving the equilibrium shape and surface energy of triangular crystals.
Amplitude Equation for a Dynamic Strain Aging Model: Beyond Linear Stability Analysis of Serrated Flow in Metallic Alloys
Authors: Rashkeev Sergey N. , Glazov Michael V. , Barlat Frédéric , Lege Daniel J. 
Published: April 2011

ABSTRACTA method for construction of “processing windows” to avoid negative strain rate sensitivity and associated serrated flow in some aluminum alloys is described. The method is based on the amplitude Ginzburg-Landau (GL) equations and analysis of bifurcation diagrams. The mathematical technique developed in the present work was applied to a specific aluminum alloy, Al-0.4%Mg-0.2%Si considered earlier in the literature [1-3], and yielded good results in terms of predicting the negative strain rate sensitivity regions in the “strain rate “temperature” parameter space. Using the GL-analysis it was demonstrated that even though the instability area is located in the region of intermediate strain rates, a qualitative difference exists between the areas of (relatively) fast and (relatively) slow strain rates. In the first case the dynamic behavior of the system is supercritical, in the second case it is subcritical. The second case is highly undesirable because it causes a sudden onset of stable stress serrations that are difficult to suppress, while in the first case the development of instability is gradual and, consequently, more easily controllable.
Growth of Cu-Ni-Sn Alloys in Pb Free CuSnAg Solder/Au-Ni Metallization Reactions
Authors: Zribi Anis , Borgesen Peter , Zavalij Lubov , Cotts Eric J. 
Published: April 2011

ABSTRACTDiffusion and phase formation were monitored in solder joints consisting of flip chips with Ni(V) under-bump metallizations bumped with Ag3.8Cu1.85Sn94.35 (atomic percentage) solder reflowed on printed circuit boards with Cu/Ni/Au metallizations. A ternary alloy, (CuNi)6Sn5, was observed to form during reflow at solder/Ni interfaces in these Ag3.8Cu1.85Sn94.35/Au/Ni solder joints. After extended thermal aging at 150 oC, a second ternary compound, (CuNi)3Sn4 forms at the Ni/(CuNi)6Sn5 interface. The growth of these alloys depletes the solder of essentially all Cu, changing its mechanical properties and melting temperature.
The Effects of a New Grain Boundary Phase in Ni-Al Alloy
Authors: Chiu Y.L. , Ngan A.H.W. , Jones I.P. 
Published: April 2011

ABSTRACTIn a γ/γ' nickel-aluminum alloy, a new phase has been identified along grain boundaries by conventional transmission electron microscopy. This phase is identified to be of the C6Cr23 type structure with lattice parameter 10.48Å, which is approximately three times that of Ni 3Al or nickel. This grain boundary precipitate is found to be coherent with the γ' phase in one grain. The chemical composition of this grain boundary precipitate is determined by energy dispersive x-ray spectroscopy and parallel electron energy loss spectroscopy. The deformation mechanism of this grain boundary precipitate is investigated on post-mortem specimens which have been carefully deformed by nanoindentation after jet-polishing.
Grain boundary structure in B2 Fe-Al ordered alloys: an atomic-scale simulation
Authors: Besson R. , Becquart C. S. , Legris A. , Morillo J. 
Published: April 2011

ABSTRACTWe calculated the atomic structure of the (310)[001] symmetric tilt grain boundary (GB) in B2 ordered Fe-Al, using empirical and ab initio potentials. Including a proper treatment of the influence of small departures from bulk B2 stoichiometry on chemical potentials through a thermodynamic point-defect model, we obtain low energy GB variants geometrically close to the usual ones deduced from the coincidence site lattice (CSL) theory. In Al-rich alloys, both methods predict GB Al segregation whereas in Fe-rich alloys, the empirical (resp. ab initio) approach leads to Fe (resp. Fe or no) segregation. With both methods, strong GB chemical effects triggered by the bulk composition appear, showing that in B2 Fe-Al, GB properties may be strongly influenced by small bulk composition changes.
Fluctuation-Induced Nucleation of PLC Bands
Authors: Sapalidis P. , Dodou D. , Hähner P. , Zaiser M. , Aifan tis E.C. 
Published: April 2011

ABSTRACTThe inuence of mesoscopic strain-rate uctuations on the n ucleation of localized deformation bands (PLC bands) in dynamically strain ageing materials is discussed. It is shown that uctuations ma y lead to a macroscopic localization of plastic ow even if linear stability analysis (LSA) of the macroscopic constitutiv e equations predicts stable deformation beha vior. The resulting quantitative corrections to linear stability analysis are evaluated, and implications for the reliabilit y of LSA results are discussed.
Influence of Antimony Doping on Nanoscale Arsenic Clusters and Dislocation Loops in Low-Temperature Grown Gallium Arsenide Films
Authors: Chaldyshev V.V. , Bert N.A. , Romanov A.E. , Suvorova A.A. , Kolesnikova A.L. , Preobrazhenskii V.V. , Putyato M.A. , Semyagin B.R. , Werner P. 
Published: April 2011

ABSTRACTTransmission electron microscopy was employed to study the microstructure of GaAs films grown by molecular-beam epitaxy at low temperature and delta-doped with Sb. Thus obtained material contained 0.5 at.% of excess arsenic that precipitates upon post-growth anneals. The Sb doping was found to strongly affect the microstructure of arsenic clusters and their ripening rate upon annealing. Segregation of Sb impurities in the As clusters was revealed. In contrast to the well known pure As clusters, the As-Sb clusters induced strong local deformations in the surrounding GaAs matrix. Relaxation of these deformations resulted in formation of dislocation loops, which was studied both experimentally and theoretically.
Influence of Oxidation On Boron Sgregation to Grain Boundaries of In-Situ Fractured Ni3Al Alloys
Authors: Koch S. A. , Agterveld D. T. L van , Palasantzas G. , Hosson J. Th. M. De 
Published: April 2011

AbstractScanning electron and scanning Auger microscopy studies were performed on in-situ fractured B-doped hypostoichiometric Ni3Al alloys. The Auger measurements on the fracture surface showed a very small amount or the total absence of B. Further, B segregated to the grain boundaries during subsequent exposure to the ambient system ultra-high vacuum environment at room temperature. The B segregation appeared to be driven by a mechanism of electronic nature related to Ni enrichment and O supplied from the environment. Ni-oxidation at room temperature is in accordance with model predictions for small beam sizes (≤10 µm) based on the premise that the electron beam creates additional nucleation sites around of which oxide growth occurs. With increasing the size of the e-beam the oxidation process becomes slower and chemisorption of oxygen plays a significant role. As a result the Ni-oxide depth decreases drastically with increasing spot size and offers an alternative route for monitoring the thickness of NiO in a nanometer range.
Segregation of Fission Products to Surfaces of UO2
Authors: Stanek C.R. , Grimes Robin W. , Bradford Mark R. 
Published: April 2011

AbstractIn order to predict the release rates of fission products from UO2 nuclear fuel, it is necessary to determine the energetics associated with their segregation from the bulk to surfaces. Here segregation is determined by calculating the total energy of a simulation repeat unit which includes a fission product, as a function of the distance of the fission product from the surface. We have investigated the possibility that specific fission products segregate preferentially to certain surfaces. In particular, Ce4+ and Zr4+ segregate to the (100) surface, while Ba2+ and Sr2+ segregate to the (111) surface. Two issues make these calculations more complex. First, charged defects need to be compensated by oxygen vacancies. For example, divalent Ba2+ and Sr2+ substituting on uranium sites are compensated by a single oxygen vacancy. Second, certain surfaces, such as the (100), are inherently unstable, but can be stabilized by oxygen vacancies. Arrangements of these surface defects lead to complex surface structures that affect segregation energetics.
Microscopic Structure and Energetics of the Pd/SrTio3 (001) Interface
Authors: Ochs Thorsten , Köstlmeier Sibylle , Elsässer Christian 
Published: April 2011

AbstractThe microscopic structure and energetics of a SrTio3 (001) surface covered with thin layers of pd were investigated by means of ab-initio electronic-structure calculations. A mixed-basis pseudopotential technique based on the local density functional theory was employed. Supercells containing srTio3 sunstrates, with either SrO or Tio2 surface terminations, and pd films of varying thicknedd were used to model the (001) surfaces and the (001) heterophase interfaces. The Tio2 terminated subtrate is energetically favoured for the adhesion of Pd films, with the Pd atoms bonded on top of the O atoms. The film adhesion is strongest for one (001) layer of fcc Pd and becomes weaker with increasing film thickness.
Activation of an Al-Zn-Mg-Li alloy by the Presence of Precipitates to be used as Sacrificial Anode
Authors: Valdez S. , Talavera M. A. , Genesca J. , Juarez-Islas J. A. 
Published: April 2011

AbstractThis work reports the influence of microstructure on the electrochemical efficiency of Al- alloys to be used as sacrificial anodes. The microstructure of as-cast Al-ingots was characterized by X-ray diffractometry and scanning electron microscope (equipped with WDS microanalysis facilities). The electrochemical behavior was investigated in 3% NaCl solution simulating sea water at room temperature. Regarding microstructure, X-ray diffractometry detected the presence of the α-Al phase, and the τ-Al2Mg3Zn3, Mg7Zn3 and δ-AlLi precipitates. SEM observations confirmed the presence of α-Al dendrites with τ-Al2Mg3Zn3 and Mg7Zn3 particles in matrix. In interdendritic regions, it was observed the presence of the eutectic α-Al + τ-Al2Mg3Zn3 plus some primary Mg7Zn3 particles. δ-AlLi particles were identified at this step only by X-ray diffractometry. Finally, it was detected that an uniform distribution of precipitates in the α-Al dendrites together with an uniform distribution of a fine eutectic gave as a result in as-cast ingots an electrochemical efficiency up to 61.4 %.
Atomistic Simulation and Density Functional Analysis of Ni(111)-ZrO2(100)(Cubic) and NiO(111)-Ni(111)-ZrO2(100)(Cubic) Interfaces
Authors: Guo Chang-Xin , Ellis Donald E. , Dravid Vinayak P. , Brewer Luke 
Published: April 2011

AbstractThe atomic arrangement and electronic structure in the vicinity of Ni(111)- ZrO2(100)(Cubic) and NiO(111)-Ni(111)-ZrO2(100)(Cubic) interfaces have been studied by atomistic simulation and by first-principles Density Functional theory. “Depth Profiling” is carred out in both methodologies, to determine modifications of cohesive energy and electron distribution of atomic layers from the interface plane. The energy profiling results show the interface consists of only a few atomic layers. Simulation results and electron density analyses are in good agreement with High Resolution Spatially Resolved Electron Microscopy data.