bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heat Treatment of Nanocrystalline Al2O3-Zr02
Authors: Smyser Bridget M. , Connelly Jane F. , Sisson Richard D. , Provenzano Virgil 
Published: April 2011

ABSTRACTThe effects of grain size on the phase transformations in nanocrystalline ZrO2-Al2O3 have been experimentally investigated. Compositions from 10 to 50 vol% Al2O3 in ZrO2 were obtained as a hydroxide gel. The powders were then calcined at 600 °C for 17 hours and heat treated at 1100 °C for 24 and 120 hours and at 1200 °C for 2 hours. The phase distribution and grain size were determined using x-ray diffraction and transmission electron microscopy. The initial grain size after calcining was 8–17 nm. It was determined that the critical ZrO2 grain size to avoid the tetragonal to monoclinic phase transformation on cooling from 1100 °C was between 17 and 25 nm. Samples containing 50% Al2O3 maintained a grain size below the critical size for all times and temperatures. The 30% Al2O3 samples showed the same behavior in all but one heat treatment. The remainder of the samples showed significant grain growth and at least partial transformation to the monoclinic phase.
Embedded Gold Clusters: Growth in Glass and Optical Absorption Spectra
Authors: Rao P. G. N. , Doremus R. H. 
Published: April 2011

ABSTRACTOptical absorption of nanosized particles in glass was measured. The plasma absorption band was completely spread out for particles below about 1.5 ran in diameter, as also has been found by gold particles in water and a polymer. The growth kinetics suggested growth of spherical particles controlled by diffusion of gold from the matrix to the particles, and a constant number of growing particles, giving a narrow size distribution of particles. For particles below about one ran in diameter (31 gold atoms), the optical absorption was proportional to λ−4, as expected if the absorption results from free electrons in the particles.
Influence of Si and W Additions on High Temperature Oxidation of γ-α2 Ti-Al Alloys
Authors: Tomasi A. , Noseda C. , Nazmy M. , Gialanella S. 
Published: April 2011

ABSTRACTTitanium aluminides have potential interest for high temperature applications because of their low density and high temperature strength. In this study the isothermal oxidation behavior in air and in the temperature range 700–850°C of γ-α2Ti-Al bulk alloys with different additions of W (0–9.5 wt.%) and Si (0–5.0 wt.%) was investigated. The samples were prepared by arc-melting starting from pure element powders (99.99%). After thermal treatments, for homogenisation and phase stabilisation, the samples were tested using a thermal analysis apparatus in order to evaluate their oxidation resistance. The oxidation rates show the beneficial effect of the W and Si additions. The growth and adherence of the protective scale on alloys have been investigated in conjunction with detailed oxide scale characterisation using the techniques of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results of the study are used for critical assessment of the oxidation mechanisms leading to the formation of surface layers of different compositions.
Effect of interstitial concentration and heat treatment on microstructure and primary creep of investment cast Ti-47Al-2Nb-2Mn with 0.8v% TiB2
Authors: Seo Dong Yi , Bieler T. R. , Larsen D. E. 
Published: April 2011

ABSTRACTMost research about creep has focused on minimum creep rate or stress rupture properties, but primary creep is important for practical applications. In this paper, we compare how interstitial content and heat treatments of shorter duration than used in past studies affect the microstructure and primary creep resistance of a particular alloy containing TiB2 particles. More time and temperature in heat treatment homogenizes the microstructure and reduces the scatter of creep times to 0.5% strain. Increasing interstitial content increases the time to 0.5% creep, and it stabilizes the a2 phase. Preliminary evidence for large mechanical twinning strains parallel to lamellar interfaces shortly following loading is provided.
Phase Stability in Processing of High Temperature Intermetallic Alloys
Authors: Perepezko J. H. , Nuñes C. A. , Yi S.-H. , Thoma D. J. 
Published: April 2011

ABSTRACTIn the development of high temperature intermetallics involving various aluminides, suicides and Laves phases, it has become evident that it is essential to consider the strong influence of materials processing throughout all stages. The underlying basis for alloy synthesis, processing and the assessment of thermal stability is established by the relevant phase equilibria, the characteristic diffusivities and the possible solidification reaction pathways. In almost all cases the microstructures of the most useful metallic alloys are multiphase assemblies in which the relative phase fractions, compositions and morphologies play key roles in optimizing the performance under high temperature conditions. The microstructure designs are usually tailored for strength, toughness, creep resistance and environmental stability and involve a balance of features derived from mixtures of a ductile phase and intermetallic phases. There is a clear experience that the level of materials processing can only be as sophisticated as the level of knowledge of the phase equilibria and the underlying kinetics. In many of the contemporary intermetallic alloys the phase stability must be considered in terms of multicomponent equilibria and non-stoichiometric intermetallic compositions. Recent developments in several important intermetallic alloy classes illustrate the guidance into alloy design and processing options provided by systematic studies of phase stability.
On the Mechanism of Milling Induced Disordering in AlFe
Authors: Clavaguera-Mora M. T. , Zhu J. , Meyer M. , Mendoza-Zelis L. , Sanchez F. H. , Clavaguera N. 
Published: April 2011

ABSTRACTThe evolution of the B2-AlFe phase during mechanical grinding in Ar has been examined as a function of milling time by X-Ray diffraction, transmission Mössbauer spectroscopy and differential scanning calorimetry. Short and long range disorder was observed to increase with the mechanical treatment up to the attainment of a steady state. The evolution of the long range order parameter and of the local atomic configurations at Fe sites were analyzed in terms of possible mechanisms for milling induced disordering. The kinetics of the thermal reordering was studied under continuous heating and isothermal calorimetrie regimes. Modeling of the reordering processes by diffusion controlled growth of pre-existing ordered grains is presented as well as the estimated values of both the enthalpy and the activation energy of the reordering process. The results are consistent with a non uniform distribution of disorder throughout the sample and will be compared with preceding information on related systems.
Effect of Initial Microstructure on the Compatibility of Rapidly Solidified Ti-Rich TiAl Powder
Authors: Nishida M. , Chiba A. , Morizono Y. , Kai T. , Sugimoto J. 
Published: April 2011

ABSTRACTInitial microstructure dependence of compactibility at elevated temperature in rapidly solidified Ti-rich TiAl alloy powders produced by plasma rotating electrode process (PREP) has been investigated. There were two kinds of powders with respect to the microstructure. The first one had a surface relief of a martensitic phase, which was referred as M powder. The second one had a dendritic structure, which was referred as D powder. α2+γ microduplex and α2/γ lamellar structures were formed in Mand D powders of the Ti-40 at%Al alloy by heat treatment at 1273 K, respectively. The microduplex structure consisted of γ precipitate in the twin related α2 matrix with the usual orientation relationship. It was difficult to compact the D powder by hot pressing at 1273 K under 50 MPa for 14.4 ks. On the other hand, the M powder was compacted easily by hot pressing with the same condition. The twin related α2 and α2 boundary changed to random ones and the α2 and γ phases were lost the usual orientation relationship in the duplex structure during the hot pressing. In other words, the low energy boundaries were changed to the high energy ones suitable for grain boundary sliding. Dislocations were scarcely observed inside of both the α2 and γ crystal grains. It was concluded that the grain boundary sliding was a predominant deformation mode in the M powder during the hot pressing. D and M powders in Ti-45 and 47 at%Al alloys showed the same tendency as those in Ti-40 at%Al alloy during hot pressing.
Stacking Faults on (001) in Transition-Metal Disilicides with The Cllb Structure
Authors: Ito K. , Nakamoto T. , Inui H. , Yamaguchi M. 
Published: April 2011

ABSTRACTStacking faults on (001) in MoSi2 and WSi2 with the Cllb structure have been characterized by transmission electron microscopy (TEM), using their single crystals grown by the floating-zone method. Although WSi2 contains a high density of stacking faults, only several faults are observed in MoSi2. For both crystals, (001) faults are characterized to be of the Frank-type in which two successive (001) Si layers are removed from the lattice, giving rise to a displacement vector parallel to [001]. When the displacement vector of faults is expressed in the form of R=l/n[001], however, their n values are slightly deviated from the exact value of 3, because of dilatation of the lattice in the direction perpendicular to the fault, which is caused by the repulsive interaction between Mo (W) layers above and below the fault. Matching of experimental high-resolution TEM images with calculated ones indicates n values to be 3.12 ± 0.10 and 3.34 ± 0.10 for MoSi2 and WSi2, respectively.
Elastic Constants of A Laves Phase Compound: C15 NbCr2
Authors: Ormeci Alim , Chu F. , Wills John M. , Chen S. P. , Albers R. C. , Thoma D. J. , Mitchell T. E. 
Published: April 2011

ABSTRACTThe single-crystal elastic constants of C15 NbCr2 have been computed by using a first-principles, self-consistent, full-potential total energy method. From these single-crystal elastic constants the isotropie elastic moduli are calculated using the Voigt and Reuss averages. The calculated values are in fair agreement with the experimental values. The implications of the results are discussed with regards to Poisson's ratio and the direction dependence of Young's modulus.
Relating Mechanical Properties with Dislocation Cores in Ni3Ge-Fe3Ge Intermetallic Alloys
Authors: John Balk T. , Kumar Mukul , Hemker Kevin J. 
Published: April 2011

ABSTRACTThe transition from positive to negative temperature dependence of 0.2% yield stress is investigated m the model pseudo-binary Ni3Ge-Fe3Ge system. Ni3Ge and Fe3Ge, both Ll2 intermetallic alloys, show complete solid solubility as Fe is continuously substituted for Ni across the composition range. However, Ni3Ge exhibits the yield stress anomaly, whereas the yield stress of Fe3Ge shows a normal decline with temperature. Mechanical testing has verified this behavior, with the anomalous behavior gradually disappearing with increasing Fe content. It is proposed that this transition results from changes in the structure of dissociated superdislocation cores. Alloys with anomalous behavior from this system are characterized by the presence of screw superdislocations locked in the Kear-Wilsdorf (KW) configuration. Conversely, alloys with normal yield stress dependence are observed to contain curvilinear superdislocations that glide on the cube planes. Results from mechanical testing are presented and correlated with TEM observations of deformation structures. These results are discussed in light of planar fault energies determined through computer simulations of images.
Mechanical Behavior of Molybdenum-Modified Cr3Si/Cr5Si3 Intermetallics
Authors: Nazmy M. , Noseda C. , Augustin S. , Lipetzky P. , Stoloff N. S. 
Published: April 2011

ABSTRACTTwo molybdenum-modified chromium suicide base intermetallics have been prepared by powder metallurgy and investigated with respect to the hardness, flexural strength and fracture toughness at different temperatures. As toughening phase, tungsten, Pt-6%Rh and Saphikon fibres were tried to improve the toughness of these two intermetallics. The tungsten fibers generated microcracks in the base material due to the large mismatch in the coefficients of thermal expansion (CTE) between the fiber and the intermetallic. The Pt-6%Rh and Saphikon fibers did not exhibit such cracking.An improvement in the fracture toughness was observed especially at elevated temperatures. The Saphikon fibers did not show interfacial reaction. Some limited diffusion of silicon was detected in the Pt-6%Rh phase after 1400°C treatment.
Electric Field Induced Control of Thin Film Diblock Copolymer Domain Orientation
Authors: Morkved T. L. , Lopes W. A. , Lu M. , Urbas A. M. , Jaeger H. M. , Mansky P. , Russell T. P. 
Published: April 2011

ABSTRACTLocal control of domain orientation in diblock copolymer thin films is demonstrated through the use of external electric fields. Thin films of a polystyrene-polymethylmethacrylate diblock copolymers, denoted P(S-b-MMA), were spin coated onto silicon nitride membrane substrates with prefabricated in-plane electrodes, forming cylindrical PMMA microdomains. Films annealed under an applied electric field (E ≤ 37V/μm) at 250°C for 24h under an argon atmosphere showed an alignment of the cylindrical microdomains parallel to the electric field lines. A quantitative measure of the degree of alignment was obtained by correlating the local field strength, E, and direction with the observed cylinder orientation. The alignment was found to saturate above E≈30V/μm, and to decrease rapidly as E falls below this value.
The Distribution of SIS Compatibilizer in Melt-Mixed Polystyrene-Polyethylene Homopolymer Blends
Authors: Kim G. , Libera M. , Potluri R. , Gogos C. G. 
Published: April 2011

ABSTRACTThis paper presents the results of transmission electron microscopy (TEM) studies on the distribution of polystyrene/polyisoprene/polystyrene (SIS) triblock copolymer compatibilizer in polystyrene-polyethylene homopolymer blends. The principal independent variable studied is the major-phase rheological properties (PSmajor/PEminor and PEmajor/PSmimor blends). The polyisoprene block was preferentially stained by OSO4 and could be clearly identified in cryo-ultramicrotomed TEM sections. The microstructural data show that when the Theologically strong PS phase is the major constituent, the compatibilizer follows the classical model localizing itself at the PS/PE interface. In the PEmajor/PSminor blends, however, the SIS compatibilizer is not localized at the PE/PS interface. Instead microdispersions of PS in SIS form which in turn are dispersed in the PE matrix. While the various microstructures are affected by the mixing protocol and polymer rheology, quiescent annealing after mixing indicates that the compatibilizer distribution is in part driven by thermodynamic effects.
Where is All the Amalgam Silvering?
Authors: Anheuser Kilian 
Published: April 2011

ABSTRACTAmalgam gilding was one of the most common techniques for the gilding of metalwork before the invention of electroplating. Its silver equivalent, amalgam silvering, was executed in the same manner, by applying a paste of silver amalgam and mercury to a copper alloy object and subsequent heating to form a diffusion bond between substrate and plating and to evaporate the excess mercury, followed by burnishing of the surface. The technical know-how was readily available. However, even though many medieval and post-medieval European metal objects were silver plated, only a few coins and small objects like medieval decorative mounts and horse trappings, and post-medieval astronomic instruments have been reported as examples of amalgam silvering. The technique was also used in China in the 3rd-1st century BC. Should we assume that there are many more amalgam silvered objects waiting to be discovered, as has been suggested? This paper investigates silver plated objects from 3rd century BC Chinese belt hooks to 18th century French decorative art and compares the analytical evidence with original silvering recipes and replication experiments, which showed that with amalgam silvering satisfactory results were far more difficult to achieve than with fire-gilding. It was found that the presence of mercury in XRF analyses of silver plated surfaces did not necessarily identify amalgam silvering, and that some allegedly amalgam silvered objects may in fact have been plated with silver chloride based electrochemical replacement silvering pastes.
Applications of Qualitative Trace Element Analyses: An Interdisciplinary Approach to Materials Conservation
Authors: Sickels-Taves L.B. , Sheehan M.S. , White G.D. 
Published: April 2011

ABSTRACTThis interdisciplinary study was designed to learn the chemical constituency of organic residues found in tabby using nondestructive analytical techniques such as X-Ray Fluorescence (XRF) and Particle Induced X-Ray Emission (PIXE). Important information pertaining to events of the past can be preserved in organic materials. The related disciplines of historic preservation and archaeology can benefit from the recovery of that information, especially when conducting collaborative research.The purpose of this study was to evaluate the effectiveness of these two techniques in their ability to characterize the chemical composition of tabby, a building material that incorporates large quantities of shell. Although useful qualitative data regarding the chemical composition of tabby was obtained using both methods, the best results were obtained using PIXE.These results suggest that PIXE represents a viable and accurate alternative for compositional analysis of materials with an organic component commonly encountered by historic preservationists and archaeologists.
Atomic-Resolution Electron Microscopy of TiB2 Precipitates in an Industrial TiAl Alloy
Authors: Inkson B. J. , Möbus G. , Rühle M. 
Published: April 2011

ABSTRACTTiB2 nano-lamellae, grown in-situ within a TiAl intermetallic melt, have been examined by high resolution electron microscopy. The use of the Stuttgart ARM enables Ti and B columns to be distinguished in the HREM images. Examination of the internal structure of the T1B2 platelets reveals extensive prismatic faulting on {1010}TiB2, {0110}TiB2 and {1100}TiB2 planes. Externally, the TiB2 platelets exhibit an orientational relationship {1010}TiB2 // {001}B2 and [0001]TiB2 // <010>B2 with interleaving platelets of B2-phase, with the predominating interface planes being {1010}TiB2 // {001}B2. The minor facets of the TiB2 platelets are [0001]TiB2 // <010>B2. {0110}TiB2 and {1100}TiB2, with the latter two facets showing no relationship with the interleaving B2-phase. No preferred orientation relationship of the TiB2 with the surrounding γ-TiAl and α2-Ti3Al phases is observed.
Boron Clustering in Silicon Under an Interstitial Flux: A Study Using Delta Doped Structures
Authors: Simpson T. W. , Mitchell I. V. , Baribeau J.-M. 
Published: April 2011

ABSTRACTUnderstanding has advanced significantly in the interpretation of the thermal release of self interstitials into a silicon lattice from a region, e.g. ion implanted, which is rich in point defects. Progress has been accelerated through the use of delta doped layer structures, especially of boron doping type, where the transient enhanced diffusion (TED) of the dopant marks the arrival of the self interstitial species from a physically separate damage region. Frequently observed in such TED experiments is an immobile, electrically inactive, boron peak on top of the spreading diffusion profile. This signature boron peak has been attributed to the Si-interstitial driven clustering of boron. It has been observed that this feature occurs for high boron concentrations and implant fluences; however, a complete understanding of the clustering mechanism has remained elusive.We present new data from experiments where the self implant fluence has been varied to allow the intensity of the transient flux to be adjusted and where repeat distances in the MBE structure have been adjusted to test for trapping. This has led to some clarifications to the current picture of boron clustering during TED. These results seem to be important in the context of the search for engineering control over dopant redistribution in Si during post-implantation annealing.
Nonhydrostatic Stress Effects on Boron Diffusion in SI
Authors: Aziz Michael J. 
Published: April 2011

ABSTRACTThe thermodynamics of diffusion under hydrostatic pressure and nonhydrostatic stress is developed for single crystals free of extended defects and is applied to the case of boron diffusion in silicon. The thermodynamic relationships obtained permit the direct comparison of hydrostatic and biaxial stress experiments and of atomistic calculations under hydrostatic stress. Assuming various values for the anisotropy in the migration strain, a currently unknown parameter, comparison is made between various measurements under hydrostatic pressure and nonhydrostatic stress, and various atomistic calculations of the volumetrics of B and Si diffusion by an interstitial-based mechanism. An independent determination of the anisotropy of the migration strain would permit a parameter-free determination of the predominant diffusion mechanism and would permit the prediction of the ratio of the diffusivity normal to the free surface to the diffusivity parallel to the surface for biaxially strained films. Procedures for measuring and calculating the anisotropy in the migration strain are described.
Release of Impurities From Structural Defects in Polycrystalline Silicon Solar Cells
Authors: McHugo S. A. , Imaizumi M. 
Published: April 2011

ABSTRACTIt is critical to understand the behavior of metallic impurities in polycrystalline silicon used for solar cells. These impurities significantly increase the minority carrier recombination rate and, in turn, degrade cell performance. Impurity gettering is a commonly used method to remove these impurities from the material, however, past work has suggested that impurity release from structural defects drastically limits the gettering process. Presently, there is only a limited understanding of impurity release from structural defects. In this work, a correlation between structural defects and the location of metal impurities in as-grown material is established and the release of nickel and copper from structural defects in polycrystalline silicon was studied in as-grown material and after sequential thermal treatments which dissolve the impurities into the silicon matrix. Synchrotron-based x-ray fluorescence impurity mapping with spatial resolution of ≈ 1μm, was used to determine impurity distributions after each thermal treatment.
Impurity Removing at Dislocations in Float Zone Silicon by Aluminium-Silicon Alloying
Authors: Perichaud I. , Martinuzzi S. 
Published: April 2011

ABSTRACTAluminium-silicon alloying is applied to dislocation-containing FZ silicon samples in order to verify if this external gettering technique is able to remove impurities trapped by these defects. Samples were scratched (front surface), bent and annealed at 750°C for 6h in order to create dislocation arrays. Standard samples and also nickel contaminated samples were investigated by light beam induced current (LBIC) mapping technique before and after alloying at 900°C for 4h with a 1 μm thick aluminium layer deposited on the backside. The LBIC technique detects the features of the dislocation array in agreement with X ray topographs. In the standard samples, the contrast is relatedto an inadvertent contamination of the samples and disappears after gettering. In the contaminated samples, dislocation contrast is higher, the aluminium treatment attenuates strongly the dislocations electrical activity but not so neatly as for the standard samples. This result is explained by the possible microprecipitation of nickel at dislocations.