bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation of Ultrafine Copper Particles in Poly (2-Vinylpyridine)
Authors: Lyons Alan M. , Nakahara S. , Pearce E. M. 
Published: March 2011

ABSTRACTUltrafine copper particles were prepared by the thermal decomposition of a copper formate-poly(2-vinylpyridine) complex. At temperatures above 125°C, a redox reaction occurs where Cu+2 is reduced to copper metal and formate is oxidized to CO2 and H2. The decomposition reaction was studied by thermogravimetric analysis, differential scanning calorimetry and mass spectrometry. Copper concentrations up to 23 wt% have been incorporated into the polymer by this technique. The presence of the polymeric ligand induces the redox reaction to occur at a temperature 80°C lower than in uncomplexed copper formate. Incorporation of the reducing agent (formate anion) into the polymer precursor enables the redox reaction to occur in the solid state. Films of the polymer precursor were prepared and the formation of metallic copper particles were studied by visible and infrared spectroscopy, x-ray diffraction techniques, and transmission electron microscopy. Results from these measurements indicate that spherical copper particles with an average diameter of 35angstrom are isolated within the polymer matrix. The particles are thermodynamically stable at temperatures up to the decomposition of the polymer matrix (≈350 °C), but oxidize rapidly upon exposure air.
Small Angle Scattering from Nanocrystalline Pd
Authors: Wallner G. , Jorra E. , Franz H. , Peisl J. , Birringer R. , Gleiter H. , Haubold T. , Petry W. 
Published: March 2011

ABSTRACTThe microstructure of nanocrystalline Pd was investigated by small angle scattering of neutrons and X-rays. The samples were prepared by compacting small crystallites produced by evaporation and condensation in an inert gas atmosphere. The strong scattering signal is interpreted to arise from crystallites embedded in a matrix of incoherent interfaces. Size distributions were deduced from the scattering curves. They consist of two parts: the crystallite size distribution dictated by the production process, and a structureless contribution due to the correlation in the spatial arrangement of the crystallites. The crystallite size distribution may be described by a log-normal distribution centred at R=2nm. The characteristic form of the correlation contribution arises from the dense packing of non-spherical crystallites. From the scattering cross-section in absolute units the volume fraction vc of crystallites was obtained as vc≈0.3, and the mean atomic density ρi in the interfaces as ρi≈0.52. The change of structural parameters during thermal annealing of the samples was studied. Up to high temperatures an appreciable volume fraction of crystallites with nearly unchanged size remains along with large particles.
Sintering of Nanophase TiO2 At 550°C
Authors: Epperson J. E. , Siegel R. W. , White J. W. , Klippert T. E. , Narayanasamy A. , Eastman J. A. , Trouw F. 
Published: March 2011

ABSTRACTSamples of nanophase TiO2 were prepared by the condensation of Ti vapors into clusters, their in situ oxidation to TiO2, and their consolidation into thin disks. Small angle neutron scattering was measured in the as-consolidated condition and after selected isothermal sintering anneals of up to 23 h at 550°C. The maximum entropy analysis method was used to obtain the size distributions of the scattering centers from the scattering curves. The results are interpreted in terms of a microstructural model consisting of nanometer sized grains of TiO2 separated by about 0.5 nm wide boundary regions, which contain voids and TiO2 of ≤60–70% of bulk density.
Characterisation of Ultrafine Microstructures Using a Position-Sensitive Atom Probe (POSAP)
Authors: Cerezo Alfred , Grovenor Chris R. M. , Hetherington Mark G. , Shollock Barbara A. , Smith George D. W. 
Published: March 2011

ABSTRACTA new development in the experimental techniques of atom probe microanalysis is described, which involves the use of a position sensitive detector system. This detector subtends a large solid angle (∼20°) at the specimen, and therefore permits the collection of ions from a substantial fraction of the whole surface area of the emitter. Progressive pulsed field evaporation leads to the construction of a three-dimensional map of the atomic chemistry of the specimen. The new instrument is ideally suited to the investigation of complex, ultrafine microstructures. Applications to the study of age-hardened aluminium alloys and Alnico permanent magnet materials are described.
Study of Multicomponent Magnetic Nanostructures with Digital Image Processing Technique.
Authors: Valanju A. P. , Jeong I. S. , Kim D. Y. , Walser R. M. 
Published: March 2011

ABSTRACTPreviously, we used Digital Image Processing (DIP) to explore the relationships between the growth morphologies of sputtered two-phase nanostructures and their soft magnetic properties [1]. In this work we extended the application of DIP to analyse the effects of deposition parameters and annealing conditions on their soft magnetic properties including disaccommodation.Magnetically soft, amorphous Co61B39 thin films, exhibiting a two-phase structure, were deposited by sequentially co-sputtering cobalt and boron. We digitized TEM micrographs of these thin films, prepared under different deposition conditions, and subjected to various post deposition processing. Digital Fourier transforms of the TEM micrographs were studied for evidence that the film anisotropy could be correlated with morphological order arising from long and short range interactions between particles over distances of ≈ 0.2 − 1.0 nm.Our qualitative studies showed that important changes in soft magnetic properties were associated with changes in the two phase morphologies. We determined, for example, that specific morphological changes were associated with the reduction in the magnetic anisotropy produced by annealing. In general, decreases in anisotropy were associated with increased isotropy in Fourier space. The largest reductions and circular symmetric 2D Fourier transforms were produced by rotating field annealing.
Critical Phenomena in Nanoscale Multilayer Materials
Authors: Tsakalakos T. , Jankowski A. 
Published: March 2011

ABSTRACTWe present a review of critical phenomena in a variety of nanoscale multilayer materials. Discontinuities of interdiffusitives at low temperatures, “the Supermodulus effect” and the “softening” of elastic constants of fcc-bcc structures, other mechanical properties at critical layer thickness are also presented. Some new calculations of elastic constants of (111) fcc and (110) bcc metallic superlattices show large changes as a function of homogeneous lattice strains. The effect of structural relaxations on a number of electronic and magnetic properties is discussed and a new analytical model is developed to explain the origin of interference effects when interfaces are apart by a few interplanar spacings. This model can predict relaxations at interfaces for a variety of materials including metals, semiconductors and ceramics.
Small Angle Neutron Scattering from Nanophase Titanium As A Function of Oxidation
Authors: Eastman J. A. , Epperson J. E. , Hahn H. , Klippert T. E. , Narayanasamy A. , Ramasamy S. , Siegel R. W. , White J. W. , Trouw F. 
Published: March 2011

ABSTRACTNanophase titanium, prepared by the gas-condensation method both as aggregated powder and in lightly compacted discs, has been studied by conventional small angle neutron scattering, and by use of contrast variation methods. The contrast has been changed (a), isotopically, by means of deuterated/protonated solvents distilled into the specimen and (b) by progressive incremental oxidation of the Ti particles using fixed doses of low-pressure oxygen. It was shown that some evolution of the small angle pattern for lightly compacted nanophase Ti occurred over a period of several months at 300 K. Contrast matching by external solvent works well and has allowed the scattering lengths of oxidized and unoxidized specimens to be followed. The results imply that the scattering from metal and oxide can be separated under suitable conditions. The partial oxidation experiments indicate that there is both a fast and slow oxidation at 300 K. Also, during slow oxidation, high scattering length density scattering centers were formed whose number increased, but whose size remained the same at about 2 nm; these centers are tentatively assumed to be TiO2.
Electrodeposited Metallic Superlattices
Authors: Lashmore D. S. , Oberle Robert , Dariel Moshe P. , Bennettf L. H. , Swartzendruber Lydon 
Published: March 2011

ABSTRACTElectrochemical deposition of artificial compositionally modulated superlattices is described. It is shown that the quality of these alloys is comparable or superior to materials produced by vapor deposition or sputtering. The ambient temperature process described by Yahalom has been modified to include a feedback and control system in order to compensate for natural convective disturbances in the electrolyte. Data is presented for copper-nickel samples of varying wavelengths down to 2 nm which suggests that magnetic properties of thin nickel layers are comparable with bulk nickel. Alloys of other types whose properties can be tailored on a near atomic scale will also be discussed along with potential applications.
Phase Control in Nanophase Materials Formed from Ultrafine Ti Or Pd Powders
Authors: Eastman J. A. 
Published: March 2011

ABSTRACTThe effect of He gas pressure during evaporation and post-evaporation O2 exposure on phase formation in nanophase materials has been examined. Ultrafine powders of Ti and Pd were prepared by the inert gas-condensation technique and bulk nanophase samples were formed by consolidation of these powders with or without prior exposure to O2. Evaporation of Ti in He pressures greater than 500 Pa followed by exposure to O2 results in the formation of ultrafine powders of crystalline rutile (TiO2) which are compacted to form nanocrystalline TiO2. Surprisingly, reducing the He pressure used during evaporation to less than approximately 500 Pa results in the formation of ultrafine powders of an amorphous phase. Room temperature consolidation of this powder under vacuum, however, results in nanocrystalline Ti being formed if the powder is not exposed to O2 prior to consolidation, and a mixture of rutile and an unidentified crystalline phase if the powder has been previously exposed to O2. Further reduction of the He pressure during evaporation of Ti to less than approximately 10 Pa results in the formation of crystalline Ti having a film-like morphology rather than than the desired ultrafine particles. Experiments on Pd evaporated in 10 to 6000 Pa of He have yielded ultrafine powders and consolidated samples of only the crystalline fcc phase, regardless of the He pressure
Metastable Nanocrystalline Carbides in Chemically Synthesized W-Co-C Ternary Alloys
Authors: McCandlish L. E. , Kear B. H. , Kim B. K. , wu L. W. 
Published: March 2011

ABSTRACTNanophase materials can be prepared either by physical methods or chemical methods. Physical methods include thermal evaporation, sputtering and melt quenching, whereas chemical methods include glow-discharge decomposition, chemical vapor deposition, sol-gel dehydration and gas-solid reaction. Recently, we have used controlled activity gassolid reactions to prepare nanophase WC-Co cermet powders at different WC loadings. In the process we have discovered some new metastable phases in the W-Co-C ternary system at temperatures below 1000 °C.
Effect of Ordering Energy on Grain Boundary Structure in L12 Alloys
Authors: Ackland G. J. , Vitek V. 
Published: March 2011

ABSTRACTAtomic structures of grain boundaries in two L12 ordered alloys with very different ordering energies have been calculated. The interatomic forces are represented by many-body empirical potentials based on the second moment approximation to the tight-binding density of states. Grain boundaries in strongly ordered alloys show very little relaxation. This results in the presence of columns of cavities in the boundaries. On the other hand boundaries in weakly ordered alloys, and also in pure f.c.c. materials, show extensive relaxations leading to much more homogeneous structures. We suggest that these structural features may be responsible for the intrinsic brittleness of grain boundaries in compounds such as Ni3Al in contrast with boundaries in pure f.c.c. metals or ordered alloys such as Cu3Au which are only embrittled by segregation.
Structural Energy Differences in Al3Ti: The Role of Tetragonal Distortion in APB and Twin Energies
Authors: Nicholson O. M. , Stocks G. M. , Temmerman W. M. , Sterne P. , Pettifor D. G. 
Published: March 2011

ABSTRACTAt stoichiometry, DO22 is the observed ground state of Al2Ti and has a C/A ratio of 2.23, but as a function of both concentration and temperature other ordered arrangements of APB's are observed. These phase transitions have sparked many studies in which the energy has been treated as that of chemical rearrangement on an fcc lattice. We have found that at the ideal C/A ratio, the Ll2 structure is lower in energy, but as the tetragonal distortion increases the DO22 energy drops below that of Ll2. The critical role played by the tetragonal distortion in the balance between Ll2 and DO22 energies precludes the use of any model based on the undistorted lattice.The major impediment to the development of Al3Ti as a high-temperature material is its lack of ductility. The standard approach is to make alloy additions which transform the structure to Ll2. An alternate approach is to work toward the enhancement of ductility in the DO22 phase. As a first step we have calculated the twinning energy in Al3Ti.
Slip Systems in Ni3(Al, Ti) At Temperatures Above the Peak in Flow Stress
Authors: Sun Y. Q. , Hazzledine P. M. 
Published: March 2011

ABSTRACTDislocations in single crystals of Ni3(Al, Ti) deformed at temperatures above the peak in flow stress have been studied by the TEM “weak-beam” technique. <110> dislocations on the primary cube plane are mostly of edge character, and they have been observed to transform into “super” Lomer- Cottrell locks. <100> dislocations, by contrast, are principally of 45° character. They are believed also to become immobilized by dissociation on {111} planes. Properties of both dislocations on cube planes are discussed and are related to the deformation behaviour of L12ordered intermetallic alloys.
In-Situ Observation of Grain Boundary Behavior in Ni3 Al Alloys During Tensile Deformation in Sem
Authors: Lin Dongliang , Chen Da 
Published: March 2011

ABSTRACTThe deformation behavior of Ni3Al alloys with various chemical compositions and subjected to different heat treatments were in-situ observed in SEN. Moreover, in-situ observations of slip trace are supplemented by the direct observation of dislocation arrangements by TEM. In boron-doped Ni3Al alloys it is shown that close to the grain boundary there exists a thin slip transition region, within which slip lines are reoriented or other slip systems are operated to produce a local strain accommodation and to relax the stress concentration at grain boundaries. However, boron-enhenced ductility is seriously affected by alloy stoichiometry, the addition of a tertiary alloy element and heat treatment, etc.
Deformation Behavior of High Temperature Intermetallic TiAl Alloyed with Gallium
Authors: Kad B. , Oliver B. F. 
Published: March 2011

ABSTRACTTiAl (γ) intermetallic has been investigated with ternary additions of up to 10 at% Ga. Optical microscopy reveals that gallium can be retained in solution to at least 7 at%. Microhardness data reveals that Ga substituted for Al such that Ti/(Al+Ga)=l causes solution softening. Deformation behavior of the single phase alloy in compression is reported. Perfect dislocations of the a/2[110] type and superdislocations of the a[011] type and a/2[112] type have been observed. TEM results indicate that primary deformation is contributed by a/2[110] type dislocations and twinning on (111) planes with wavy slip optically observed
WORKHA RDENING AND NON-OCTAHEDRAL SLIP SYSTEMS IN ORDERED Cu2NiZn
Authors: Morris D. G. , Morris M. A. , Biselli C. 
Published: March 2011

ABSTRACTThe ordered Cu2NiZn alloy is virtually unique in showing a changing antiphase domain structure according to annealing temperature. At low annealing temperatures there are isotropic domains and at high annealing temperatures there are cube-oriented domains characteristic of highly anisotropic boundary energies. This property allows a comparison of dislocation behaviour for otherwise identical materials: the roles of cube crossslip and cube glide can then be distinguished from other mechanisms, for example elastic torque effects and dipole formation. Mechanical properties and dislocation structures are examined over a range of test temperatures. The material having cube-oriented domain boundaries shows a much higher work hardening rate over an intermediate temperature range. Strengthening at low temperatures is dominated by dipole and multipole formation, whilst deformation above ambient temperature leads to the appearance of non-octahedral glide, more frequently on planes near {110} than near {001}. For the material with cube-oriented domain boundaries there is some evidence to suggest point blockage by cross-slip onto cube planes, leading to the higher work hardening rate at the intermediate temperature. This study emphasizes the multiplicity of slip systems which may operate and discusses the relative importance of anisotropic antiphase boundary energies and anisotropic elasticity effects.
Creep-Fatigue Resistance of a Nickel-Aluminide
Authors: Tien J. K. , Bellows R. S. 
Published: March 2011

ABSTRACTA modified fatigue test matrix that provided both creep (high mean stress) and fatigue (alternating stress) damage was used to evaluate the creep-fatigue behavior of D.S. Ni3Al(B,Hf). The three generic regimes of below, at, and above peak yield strength temperature were investigated. It was found that the creep-fatigue resistance of this intermetallic remains high through the three temperature regimes, allowing it to be further considered as a monolith or as the matrix of high-temperature fiber reinforced composite.
Some Thermodynamic Properties of NiAl Calculated by Molecular Dynamics Simulations
Authors: Clapp P. C. , Rubins M. J. , Charpenay S. , Rifkin J. A. , Yu Z. Z. , Voter A. F. 
Published: March 2011

ABSTRACTCalculations of the surface free energy and anti-phase boundary energy as a function of low index orientations and temperature have been determined for equiatomic perfectly ordered bcc NiAl via molecular dynamics computer simulations. The simulations utilized an Embedded Atom Method calculation of the interatomic potentials and volume forces in the Ni-As alloy system. Values of about 0.95, 1.6, 1.9 and 2.0 J/m2 were found for surface energies of the {100}, {110}, {112} and {111} orientations:, respectively. APB energies of about 0.24 and 0.38 J/m2 were determined for {110} and {112} boundaries, respectively. In addition, we have examined the phase stability and relative energies of the ordered bcc, fcc and bct phases at low temperature, and find a bct phase with c/a = 1.32 slightly lower in energy than the bcc, presaging the martensitic transformation that occurs at finite temperatures in more nickel rich alloys.
Mechanical Properties of Diverse High-Temperature Compounds–Thermal Variation of Microhardness and Crack Formation
Authors: Fleischer Robert L. 
Published: March 2011

ABSTRACTMicrohardness vs temperature and elastic moduli have been measured for a suite of intermetallic compounds that melt above 1400°C. Binary intermetallics were selected to represent a variety of crystal structures and yet have optimal combinations of high melting temperature (Tm) and low specific gravity. Some deliberately two-phase alloys were prepared in which one phase is a terminal-phase metal and the other an intermetallic compound.Binary compounds can be described by two patterns. In those where plasticity is difficult, hardness decreased slowly with temperature up to Tm/2, the decrease being no more than that normally shown by the elastic moduli. In those compounds where single crystal plasticity is known (or at least plausible), microhardness decreases more rapidly than do elastic moduli, presumably due to thermally activated slip.
Parameters for Ductility Improvement in TiAl
Authors: Kawabata T. , Tamura Takashi , Izumi O. 
Published: March 2011

ABSTRACTThe effect of the Ti/Al ratio and third elements (Cr, Hf and Nb) on the mechanical properties of TiAl has been studied. Solution hardening in these elements is so large that, e.g., the strength doubles by the addition of 3 at.% Cr. Ductility to fracture strain has been improved up to 2.7 % and 2.7 % by the Cr addition and the use of high purity base metals, respectively. Parameters relating to the improvement of ductility have been discussed. Namely, the improvement of ductility was caused by the decreases of the grain size, axial ratio and impurity. A hypothesis has been proposed that the ductility improvement was related with the excess shrinkage of volume of a unit cell due to the addition of the third element which implies the strengthening of chemical bonds and vice versa. The effect of twins and a lamellar structure with the plate-like Ti3Al and the matrix on the ductility have been discussed.
Microstructure and Mechanical Properties of Ll2-Structure Alloys Based on Al3Zr
Authors: Schneibel J. H. , Porter W. D. 
Published: March 2011

ABSTRACTThe tetragonal compound Al3Zr can be transformed into the cubic Ll2 structure by additions of Cr, Fe, Ni or Cu. This result is interpreted in terms of Pettifor's structure map. The transformation is accompanied by substantial softening. The significant porosity of cast buttons which develops during the homogenization required to produce the Ll2 structure is attributed to the Kirkendall effect. Al-5.5Fe-25Zr (at. %) specimens with the Ll2 structure can be deformed at room temperature in compression, and their yield stress has been determined as a function of temperature. Al-Fe-Zr is nevertheless a brittle material. This is illustrated for Al-Fe-V-Zr Ll2-structure compound, the fracture toughness of which is only slightly higher than that of sintered SiC. Evidence is presented to suggest that Ll2 formation is accompanied by an increase in toughness. Significant improvements in the mechanical properties of Al3Zr-type alloys may possibly be achieved by improved processing.
Effect of Strain Rate on the Plastic Behaviour of Ll2Compounds Based on Ni3Al
Authors: Miura Seiji , Ochiai Shouichi , Oya Yoshihiro , Mishima Yoshinao , Suzuki Tomoo 
Published: March 2011

ABSTRACTIn both single and polycrystalline Ni3Al, no strain rate dependence of 0.2% flow stress is observed in a temperature range where anomalous positive temperature dependence of strength is exhibited. A distinct strain rate dependence is observed, however, in single crystals when the test temperature is raised beyond the peak in flow stress. It is shown that (111) type slip involving diffusional process is responsible for the strain rate sensitivity at near [001] orientation, while (001) type slip which is governed by the Peierls mechanism at orientations away from [001]. In polycrystalline compound with a fine grain size an apparent loss of the positive temperature dependence of strength is observed at a slower strain rate due to grain boundary sliding.