bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microstructure Evolution in Charged Particle Irradiated 316 SS Modified to Reduce Radiation Damage
Authors: Gan J. , Simonen E. P. , Edwards D. J. , Bruemmer S. M. , Sencer B. H. , Fournier L. , Was G. S. 
Published: April 2011

ABSTRACTThe objective of this work is to investigate the addition of misfit elements in both size and mass on the evolution of irradiated microstructure in 316 SS. Alloys were modified by the addition of Pt and Hf to suppress the radiation damage. Pt and Hf were added as a lattice perturbation to catalyze defect recombination within the early stage of cascade formation and defect migration. Irradiations were conducted with 5 MeV Ni-ions at 500 °C to doses up to 50 dpa or with 3.2 MeV protons at 400 °C. Microstructures were characterized using transmission electron microscopy. While no beneficial effect was seen for Pt addition, Hf appears to effectively alter the microstructural response to irradiation.
Nature of the Fine-Scale Defects and Radiation Hardening in Stainless Steels Neutron-Irradiated at 550K
Authors: Edwards D. J. , Simonen E. P. , Bruemmer S. M. 
Published: April 2011

ABSTRACTOur understanding of radiation effects in stainless steels irradiated at temperatures below annealing stage V (<573K) remains unclear. The microstructure under these conditions has been loosely described in terms of Frank loops and “black spot” damage, the latter of which is typically considered to be 4-5 nm or less in size. To further clarify the nature of these defects, 6 stainless steels heats neutron irradiated at 550K from 0.6 to 13.3 dpa have been characterized by TEM. The microstructure is comprised of a very high density of small Frank loops present in sizes as small as 1 nm and perhaps lower, which could be of both vacancy and interstitial-type. The density of the visible loops is already established at the lowest dose available, however, the microstructure continues to evolve as the dose increases. The size distributions of the Frank loops change from a narrow symmetric distribution to a much broader size distribution with a bimodal distribution beginning to form at the higher doses.
Heavy Ion Irradiation of Brannerite-type Ceramics
Authors: Lian Jie , Wang Lumin , Lumpkin Gregory R. , Ewing Rodney C. 
Published: April 2011

ABSTRACTBrannerite, UTi2O6, occurs in polyphase Ti-based, crystalline ceramics that are under development for plutonium immobilization. In order to investigate radiation effects caused by α- decay events of Pu, several brannerite compositions were synthesized: UTi2O6, ThTi2O6, CeTi2O6 and a more complex material, which is composed of Ca-containing brannerite and pyrochlore. An 1 MeV Kr+ irradiation was performed over a temperature range of 25 K to 1020 K with in-situ TEM. The ion irradiation-induced crystalline-to-amorphous transformation was observed in all brannerite samples. At room temperature, the critical amorphization dose, Dc, resulting from Kr+ ion irradiation increases in the order: Dc (CeTi2O6) < Dc (ThTi2O6) < Dc (Ca- containing brannerite) < Dc (UTi2O6) < Dc (Ca-containing pyrochlore). The critical amorphization dose for stoichoimetric brannerite increases at elevated temperature due to the effect of thermal annealing. The critical amorphization temperatures of the different brannerite compositions are: 970 K, UTi2O6; 990 K, ThTi2O6; 1020 K, CeTi2O6. The effects of structure and chemical composition on radiation resistance of brannerite-type and pyrochlore-type ceramics are discussed.
Kinetic Monte Carlo simulations of cascades in Fe alloys
Authors: Domain C. , Becquart C.S. , van Duysen J.C. 
Published: April 2011

ABSTRACTThe Pressurized Water Reactor vessel steels are embrittled by neutron irradiation. Among the solute atoms, copper play an important role in the embrittlement and different Cu-rich defects have been experimentally observed to form. We have investigated by Kinetic Monte Carlo (KMC) on rigid lattices the evolution of the primary damage. Since the point defects created by the displacement cascades have very different kinetics, their evolution is tracked in two steps. In a first step, we have studied their recombination in the cascade region and the formation of interstitial clusters using “object diffusion”. The parameters of this model are based on MD simulations, or on first principles calculations. In a second part, we have investigated the subsequent evolution of the primary damage with a model based on a vacancy jump mechanism. These simulations which rely on an adapted EAM potential show the formation of copper rich defects. Some of the potential's predictions that played a key role in the model were checked by ab initio calculations. The defects obtained from these simulations, subsequent to the primary damage created by displacement cascades, exhibit similarities with the ones observed by atom probe. The influence of temperature and Cu content on the final damage was investigated.
MD Refinement of Topologically Simulated Irradiation Cascades in Silica
Authors: Yuan Xianglong , Pulim Vinay , Hobbs Linn W. 
Published: April 2011

ABSTRACTRefinement of several topologically generated displacement cascades in silica has been conducted using molecular dynamics (MD) simulation. Several metastable amorphous silicas with substantially different medium-range order (as characterized by ring topologies) were obtained. However, their total correlation functions were found scarcely distinguishable. Major structural reconstruction was observed when the refinement took place above a glass transition temperature, below which the cascades largely retained their original topological ring structures. Attempts are made to correlate topological ring distributions with the first sharp diffraction peak, which may in turn provide some insight into the medium range structures of irradiated silicas.
The Influence of PKA Direction on Displacement Cascade Evolution
Authors: Stoller Roger E. 
Published: April 2011

ABSTRACTAn extensive database of atomic displacement cascades in iron has been developed using molecular dynamic simulations. More than 300 cascades have been completed at 100K at energies between 100 eV and 100 keV, with fewer simulations at 600 and 900K. A systematic evaluation of the database has revealed an unexpected influence of PKA direction in low energy simulations. For primary knockon (PKA) directions that lie in the close-packed {110} planes, the cascade tends to be constrained to develop in only two dimensions. This planar “channeling” leads to much higher point defect survival than when a random high-index PKA direction is used to initiate the cascade. For example, the average number of stable Frenkel pair produced in 300 eV cascades is about 2.1 for cascades initiated with a [135] PKA, and 3.2 for [114] cascades. Some influence of this PKA direction effect was observed for energies up to 2 keV. The interstitial clustering behavior also appears to be affected in cascades with high defect survival.
An Analysis of the Structure of Irradiation induced Cu-enriched Clusters in Low and High Nickel Welds
Authors: Hyde Jonathan M. , English Colin A. 
Published: April 2011

ABSTRACTTwo high copper irradiated welds, one containing very low Ni and the other containing very high Ni, have been examined using 3-D atom probe (3DAP) microscopy, small angle neutron scattering (SANS) and field emission gun-scanning transmission electron microscopy (FEG- STEM).Irradiation induced clusters were observed in both welds. They were found to be significantly smaller and exist at a higher number density in the high Ni weld. A new algorithm was developed to precisely identify the shape, composition and size of clusters observed in the atom probe data. Representative irradiation induced clusters from each weld were then examined in greater detail. They were shown to be ramified and have a significant Fe content (∼60at.%). Cu was found to be more strongly associated with the core of the clusters than Mn or Ni. In the low Ni weld, there was evidence for P at the interfaces between the clusters and matrix. Cluster composition estimates from FEG-STEM analyses were consistent with those observed by 3DAP microanalysis. For each weld, the mean radius of gyration of the clusters was found to be almost identical to the radius of gyration determined directly from SANS analyses of these materials. Finally, the number density of features was estimated from the SANS data by using the compositional information from the 3DAP observations. Consistency with the number density calculated directly from the 3DAP data was obtained provided that it is assumed that the clusters exhibit some magnetic properties.
Atomistic Simulation of Vacancy and Self-Interstitial Diffusion in Fe-Cu Alloys
Authors: Marian Jaime , Wirth Brian D. , Perlado J. Manuel , Odette G. R. , de la Rubia T. Diaz 
Published: April 2011

ABSTRACTNeutron hardening and embrittlement of pressure vessel steels is due to a high density of nanometer scale features, including Cu-rich precipitates which form as a result of radiation enhanced diffusion. High-energy displacement cascades generate large numbers of both isolated point defects and clusters of vacancies and interstitials. The subsequent clustering, diffusion and ultimate annihilation of primary damage is inherently coupled with solute transport and hence, the overall chemical and microstructural evolutions under irradiation. In this work, we present atomistic simulation results, based on many-body interatomic potentials, of the migration of vacancies, solute and self-interstitial atoms (SIA) in pure Fe and binary Fe-0.9 and 1.0 at.% Cu alloys. Cu diffusion occurs by a vacancy mechanism and the calculated Cu diffusivity is in good agreement with experimental data. Strain field interactions between the oversized substitutional Cu solute atoms and SIA and SIA clusters are predominantly repulsive and result in both a decreased activation energy and diffusion pre-factor for SIA and small (N <5) SIA cluster migration, which occurs by three-dimensional motion. The Cu appears to enhance the re- orientation of the SIA clusters to different <111> directions, as well as the transition from <110> to mobile <111> configurations. The migration behavior of larger SIA clusters, which undergo only one-dimensional diffusion during molecular dynamics timescales, is largely unaffected by the Fe-Cu alloy, although SIA clusters are effectively repelled by coherent Cu precipitates.
Synthesis of III-Nx-V1-x Thin Films by N Ion Implantation
Authors: Yu K. M. , Walukiewicz W. , Shan W. , Wu J. , Beeman J. W. , Ager J. W. , Haller E. E. , Ridgway M. C. 
Published: April 2011

ABSTRACTDilute III-Nx-V1-x alloys were successfully synthesized by nitrogen implantation in GaAs and InP. The fundamental band gap energy for the ion beam synthesized III-Nx-V1-x alloys was found to decrease with increasing N implantation dose in a manner similar to that commonly observed in epitaxially grown GaNxAs1-x and InNxP1-x thin films. The fraction of N occupying anion sites (“active” N) in the GaNxAs1-x layers formed by N implantation was thermally unstable and decreased with increasing annealing temperature. In contrast, thermally stable InNxP1-x alloys with N mole fraction as high as 0.012 were synthesized by N implantation in InP. Moreover, the N activation efficiency in InP was at least a factor of two higher than in GaAs under similar processing conditions. The low N activation efficiency (<20%) in GaAs can be improved by co-implanting Ga and N in GaAs.
A Damage Model for Disordered Structures in Ion Irradiated Silicon
Authors: Cheng Ju-Yin , Gibson J. Murray 
Published: April 2011

ABSTRACTMedium-range order has been observed in ion-implanted amorphous silicon, suggesting a paracrystalline structure for this material. The origin of a paracrystalline structure may be due to an energy spike phenomenon. To evaluate the influence of energy spikes on a particular process, we have attempted to calculate the characteristic energy in a spike. However, the observed depth dependence of amorphous structures in as-implanted silicon is puzzling. To explain this, we simulated the depth distribution of cascade events in a particular energy range. We found a great increase of point defect concentration and cascade events as the depth increases. This result could explain the experimental depth dependence.
Impact of Boron and Gallium on Defects Production in Silicon
Authors: Khan Aurangzeb , Dharmarasu Nethaji , Yamaguchi Masafumi , Araki Kenji , Vu Tuong K. , Saga Tatsuo , Abe Takao , Annzawa Osamu , Imaizumi M. , Matsuda Sumio 
Published: April 2011

ABSTRACTWe report the results of comparison of radiation-induced defects (1 MeV electrons) in n+-p-p+ Si diodes doped with gallium or boron ranging in concentration from 8 × 1014 to 5 × 1016 cm-3, together with the impact of oxygen on radiation –induced defects. Present results provide evidence for new defects states in addition to those previously reported in gallium- and boron-doped Si. The combined boron and gallium data provide enough information to gain valuable insight into the role of the dopants on radiation-induced defects in Si. The interesting new future of our results is that the gallium appears to strongly suppress the radiation induced defect, especially hole level EV+0.36 eV, which is thought to act as a recombination center. Similarly the dominant electron level at EC-0.18 eV in B-doped Si (which act as a donor) has not been observed in Ga-doped CZ-grown Si.
Grain Boundary Dynamics: A Novel Tool for Microstructure Control
Authors: Gottstein G. , Molodov D.A. , Shvindlerman L. S. , Winning M. 
Published: April 2011

ABSTRACTThe reaction of grain boundaries to a wide spectrum of forces is reviewed. Curvature, volume energy and mechanical forces are considered. The boundary mobility is strongly dependent on misorientation, which is attributed to both grain boundary structure and segregation. In magnetically anisotropic materials grain boundaries can be moved by magnetic forces. For the first time a directionality of boundary mobility isreported. Flat boundaries can also be moved by mechanical forces, which sheds new light on microstructure evolution during elevated temperature deformation. Curvature driven and mechanically moved boundaries can behave differently. A sharp transition between the small and large angle boundary regime is observed. It is shown that grain boundary triple junctions have a finite mobility and thus, may have a serious impact on grain growth in fine grained materials. The various dependencies can be utilized to influence grain boundary motionand thus, microstructure evolution during recrystallization and grain growth.
A phase field model of the premelting of grain boundaries in pure materials
Authors: Lobkovsky Alexander E. , Warren James A. 
Published: April 2011

ABSTRACTWe present a phase field model of solidification which includes the effects of the crystalline orientation in the solid phase. This model describes grain boundaries as well as solid-liquid boundaries within a unified framework. With an appropriate choice of coupling of the phase field variable to the gradient of the crystalline orientation variable in the free energy, we find that high angle boundaries undergo a premelting transition. As the melting temperature is approached from below, low angle grain boundaries remain narrow. The width of the liquid layer at high angle grain boundaries diverges logarithmically.
Dislocation patterning: tochastic approach to mesoscale modeling
Authors: Häahner Peter 
Published: April 2011

ABSTRACTPlastic deformation by dislocation glide is known to be associated with the spontaneous formation of mesoscopic patterns of various types, e.g. cellular dislocation structures during unidirectional deformation and quasi-periodic persistent slip band structures during cyclic deformation. hile it is recognized that dislocation patterning represents a dissipative far-from-equilibrium process, theoretical modelling of those phenomena is complicated by the long-range nature of dislocation interactions inducing collective dislocation behaviour on a mesoscopic scale. n this paper the problem is addressed using a stochastic approach with random uctuations acting on the evolution of the dislocation ensemble. he intensity of the uctuations is determined self-consistently from dynamic dislocation interactions and, hence, re ects correlated dislocation motion. t is shown that those uctuations may induce dislocation patterns by stabilizing non-uniform dislocation distributions. icrostructure-based models are presented for unidirectional and cyclic plastic deformation. n the rst case fractal dislocations distributions corresponding to hierarchically organized dislocation cell structures are obtained, while in the latter case a decomposition into dislocation-rich walls or veins and depleted channels is found, which are associated with the formation of persistent slip bands and matrix structures. he good agreement with experimental observations in single-crystalline f.c.c. metals points at the importance of collective dislocation e ects in the self-organization of those structures.
A microstructure evolution model including dislocation plasticity
Authors: Cleri Fabrizio , D'Agostino Gregorio 
Published: April 2011

ABSTRACTWe present a stochastic microstructure evolution model applicable to grain growth and its recent extensions, in particular relative to dislocation plasticity. The model is implemented by means of numerical simulations based on the velocity Monte Carlo algorithm. It describes the evolution of a two-dimensional microstructure by tracking the motion of triple junctions, i.e. the vertices where three grain boundaries meet. Grain boundaries can be modeled as straight or curved segments; the misorientation dependence of both grain-boundary energies and mobilities can be included, as well as grain rotation. We show simple examples of normal, abnormal and oriented grain growth. The model is already capable of dealing with a two-phase (liquid-solid) system, to simulate both grain growth and grain dissolution in the liquid. Finally, we report preliminary results of a recent extension of the model to include mechanical deformation from dislocation plasticity.
Forces between Dislocations due to Dislocation Core Fields
Authors: Henager Charles H. , Hoagland Richard G. 
Published: April 2011

ABSTRACTAtomistic dislocation models were used to determine the properties of dislocation core fields in Al using an EAM potential. Equilibrium atom configurations were compared with initial configurations displaced according to the Volterra field to determine core displacement fields for edge, screw, and mixed (60° and 30°) geometries. The core field was approximated by a line force defect field lying parallel to the dislocation line direction. Best-fit parameters for the core fields were obtained in terms of the anisotropic elastic solution for a line force defect, from which the line force strengths and the origin of the line forces were determined. The line force stress fields were then used to compute the forces between dislocations for several dislocation configurations. The Volterra field dominates beyond 50b but core field forces modify the equilibrium angle of edge dislocation dipoles and determine the force between otherwise noninteracting edge and screw dislocations at distances out to 50b compared to the Volterra-only forces.
Genesis of Defects in Massively Transformed L10-ordered τ-MnAl Alloys
Authors: Yanar Cagatay , Radmilovic Velimir , Soffa William. A. , Wiezorek Jorg M. K. 
Published: April 2011

ABSTRACTDefects produced in massively transformed L10-ordered τ-MnAl have been characterized by detailed TEM studies. The defect population in massive τ-MnAl comprises arrays of overlapping stacking faults, {111}-conjugated microtwins, thermal antiphase boundaries and dislocations. The genesis of these defects has been attributed to atomic attachment faulting on {111}- and {020}-type facets of the essentially incoherent growth interface between the parent and product phases. The features of the defect genesis in τ-MnAl are discussed with respect to the role of atomic level processes at solid-state transformation interfaces in general and growth interfaces in massively transforming materials systems in particular.
Influence of Fe on the Morphology of Spinel in the System MgO-Al2O3-Fe2O3.
Authors: Kharissova O.V. , Ortiz U. , Hinojosa M. 
Published: April 2011

AbstractThe investigation of the morphology of crystalline solids surfaces is of practical and general interest because many processes such as the growth of epitaxial films, catalytic reactions and others, are intimately connected with surface conditions. In this work we study the surface morphology and structure of the spinel as produced in the system MgO- Al2O3-Fe2O3 at 1400°C for 15 h in a conventional furnace and in a microwave oven for 30 min. The spinel was analyzed by X-ray diffraction, scanning electron microscopy (SEM), X-ray spectrometry (EDX), and atomic force microscopy (AFM). The AFM images were recorded in the contact mode. Images scanned at different magnifications show steps and flat terraces. Experimental observations were made on the nature and distribution of the observed polygonal morphology.
Oxygen Exchange on a Highly Oriented Thin Film Electrode
Authors: Yang Y. L. , Chen C. L. , Luo G. P. , Chu C. W. , Jacobson A. J. 
Published: April 2011

AbstractThe cathodic kinetic processes on a highly oriented LSCO thin film electrode supported on YSZ(100) surface were studied with a 3-probe ac impedance method under varying bias potential and annealing temperatures. Three distinctive features observed in the impedance spectra were assigned to contributions from the ionic conduction of the YSZ electrolyte, the ionic transfer at the LSCO/YSZ interface, and the oxygen exchange on the LSCO electrode surface. The changes of the three features with respect to the annealing history and bias potential were measured. The impedance data were analyzed using an equivalent circuit model: (RelCel)(RinterfaceQinterface)(RsurfCsurf).
Microstructure of Sputter Deposited TiO2/SiO2 Multilayer Optical Coatings
Authors: Sutter E. , Sutter P. , Moore J.J. 
Published: April 2011

AbstractThe microstructure of TiO2/SiO2 multilayer optical filters has been investigated in detail by cross-sectional transmission electron microscopy and related to their optical properties and stability. The amorphous TiO2 layers in the as-deposited multilayers are found to consist of nanocolumns and intercolumnar regions with non-stoichiometric or lower density material. In humid ambients this microstructure absorbs moisture which causes a shift in the absorption edge of the filters. Upon annealing the TiO2layers are found to recrystallize into the low-temperature anatase modification which leads to significantly improved stability of the optical properties of the filters.
Characterization of Oxide Layers of Bulk Si1-xGex
Authors: Suzukake W. , Nemoto S. , Iida T. , Takanashi Y. , Sakuragi S. 
Published: April 2011

AbstractBulk crystals of Si0.4Ge0.6, grown using the vertical Bridgman method, were oxidized at 800 °C for 1 h using oxygen in dry oxidation and a stream of de-ionized water in wet oxidation. Single-like and polycrystalline Si0.4Ge0.6samples were used. The oxidized samples were analyzed using x-ray photoelectron spectroscopy to determine the chemical states of the Si and Ge in the oxide. In the sample oxidized using a dry ambient, the oxide layer consisted mainly of SiO2, and GeO2 formed the subsurface area only. This can be accounted for by the differences in the formation of the free energies of the SiO2 and GeO2. In wet oxidation, the oxide layer had a mixed structure consisting of SiO2 and GeO2. To understand the oxide formation mechanisms in the wet oxidation process, an introduction of a chemical bond manipulation explained the formation of the mixed structure.