bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formation of Fine γ Grain Structure Through Fine α2 / γ Lamellar Structure in Ti-Rich TiAl Alloy
Authors: Kumagai T. , Abe E. , Nakamura M. 
Published: April 2011

ABSTRACTMicrostructural development of an extremely fine α2-Ti3Al / γ-TiAl lamellar structure, which was formed by ice water quenching after solution-treatment in a high-temperature α-Ti phase field for a long period of time, was examined during isothermal aging treatment. In an as-quenched Ti-48at.%Al alloy, the massively transformed γ (γm) and untransformed (meaning massively untransformed) fine α2/γ lamellar regions were observed. Fine γ grains, which were similar to γm, were generated both within the fine α2/γ lamellae and at the boundary area between the γm and the fine α2/γ lamellar regions by aging at a low-temperature (1173K) for a short time (180s). Further aging (1.8ks) caused the coarsening of these newly generated fine γ grains. On the other hand, the coarsening of the γ grains occurred by a high-temperature (1323K) aging treatment even for 180s. Fine α2 plates and particles, which were aligned to a particular direction, were observed in the γ grain interiors, indicating that the newly generated γ grains grew at the expense of the fine α2/γ lamellae. It can be considered that the γ grain formation through the fine α2/γ lamellae is closely related to the α2→γ reaction of the α2 plates sandwiched by the γ plates, and needs the fast heating rate enough to overcome the α2/γ → γ/γ lamellae reaction.
Tensile and Compression Testing of Single-Crystal Gamma Ti-55.5 Al
Authors: Zupan Marc , LaVan David , Hemker K. J. 
Published: April 2011

ABSTRACTThe orientation and temperature dependence of the flow strength of γ-TiAl is being measured to promote a fundamental understanding of the deformation mechanisms that are active in this alloy. High quality single crystals of γ- Ti-55.5 Al have been grown using an optical float zone furnace, which allows for crystal seeding and provides a containerless growth environment. These crystals have been oriented using back reflection Laue and TEM and cut into microsample tensile specimens by electric discharge machining. The microsample testing technique developed at Johns Hopkins [1] is being utilized to measure the orientation, temperature and tension/compression dependence of the flow strength of TiAl. An outline of the microsample testing techniques that have been developed for this study and preliminary results follow in this paper.
Ultrafine Fully-Lamellar Structures in Two-Phase γ-TiAl Alloys
Authors: Maziasz P. J. , Liu C. T. 
Published: April 2011

ABSTRACTSpecial ultrafine fully-lamellar microstructures have been found recently in γ-TiAl alloys with 46–48 at.% Al, when they are processed or heat-treated above the α-transus temperature (Tα). Hot-extrusion above Tα also produces a refined colony or grain size. Refined-colony/ultrafine-lamellar (RC/UL) microstructures produce an excellent combination of room-temperature ductility and high-temperature strength in Ti-47Al-2Cr-2Nb (at.%) alloys. UL structures generally have an average interlamellar spacing of 100–200 nm, and have regularly alternating γ and α2 lamellea, such that they are dominated by γ/α2 interfaces with relatively few γ/γ twin boundaries. The focus of this study is how variations in processing parameters or alloy composition affect formation of the UL structure, particularly the α2 component.
Comparison of the Creep Properties of Cast and Powder Metallurgy-Extruded Binary NiAl
Authors: Raj S. V. , Garg Anita , Bieter Thomas R. 
Published: April 2011

ABSTRACTA comparison of published creep data on binary NiAl showed that there is a discrepancy in the reported magnitudes of the stress exponents, n, which usually vary between about 4.5 and 6.5. In general, a close examination of the data suggested that n ≈ 4.5 for cast materials arid 6.5 for powder-metallurgy extruded NiAl. Constant load compression creep tests were conducted on a cast and extruded binary NiAl between 800 and 1200 K over a wide range of initial applied stresses varying between 4.0 and 200 MPa. The microstructures were characterized by transmission electron microscopy. The observed variations in the creep behavior of the extruded cast and powder-metallurgy NiAl appeared to be due to a grain size effect. Despite similarities in the values of n, no significant substructure was observed in most of the grains in the cast and extruded specimens at 1100 and 1200 K in contrast to the PM-extruded alloy, which revealed a wide range of substructural features in the power-law creep region. However, extensive subgrain formation and dislocations were widely observed at lower temperatures and higher stresses in the cast and extruded material.
Strain Rate Sensitivity of Mechanical Properties and Related Thermal Activation Process in a Two-Phase γ Titanium Aluminide
Authors: Lin Dongliang , Lin T. L. , Wang Yu , Lin Yun , Kim Young-Won 
Published: April 2011

ABSTRACTTensile properties of a two-phase γ titanium aluminide with duplex microstructure are tested under different strain rates from 5×10-5 to 5×10-3S-1 at temperature from 1123K to 1273K. It is found that there exists approximate linear relationship between the flow stresses and the logarithm of the strain rate at different temperatures. The strain rate sensitivity can be explained by thermal activation theory, and dislocation climbing is identified as the rate controlling mechanism
Yield Point Phenomenon and Serrated Yielding in Nb-40Ti-15Al
Authors: Perungulam S. , Wheeler R. , Hou D. H. , Grylls R. J. , Banerjee S. , Fraser H. L. 
Published: April 2011

AbstractThe ternary Nb-40Ti-15Al (at%) intermetaltic has an ordered B2-type crystal structure and shows appreciable ductility. Deformation is mainly accommodated in slip bands by the glide of b=l/2<lll> dislocations on {110} planes. The tensile behavior of this material has been studied at room temperature and at intermediate temperatures. Static and dynamic strain aging have been observed in certain temperature regimes. A model based on dislocation pinning by precipitates is proposed to explain the serrations observed during dynamic strain aging.
Platinum Group Metals Base Refractory Superalloys
Authors: Yamabe-Mitarai Y. , Koizumi Y. , Murakami H. , Ro Y. , Maruko T. , Harada H. 
Published: April 2011

ABSTRACTIr- and Rh-base refractory superalloys with an fee and Lb two phase structure similar to Ni-base superalloys, yet with considerably higher melting temperatures have been proposed. Fee and Ll2two phases were observed in these alloys by transmission electron microscopy and X-ray powder diffractometry. The compression tests of these alloys showed that the strengths of several alloys were about 200 MPa at 1800 °C and these alloys have potential to become ultra-high temperature materials for use in power engineering field.
The Role of Copolymer Architecture on the Interfacial Structure of a Ternary Polymer Blend
Authors: Dadmun M. D. 
Published: April 2011

ABSTRACTThe role of copolymer sequence distribution on the interfacial characteristics of a ternary polymer blend containing 2 homopoiymers and a copolymer in the phase separated state are examined using Monte Carlo Simulation. The copolymer does migrate to the biphasic interface in the phase separated regime while the configuration and expansion of the copolymer at the interface is a function of sequence distribution within the copolymer. This effect is interpreted in terms of the efficiency of the copolymer to strengthen the biphasic interface. These results suggest that block, alternating, and block-ran structures show promise as interfacial modifiers, while the purely random and alt-ran copolymers will be less efficient as an interfacial strengthener. It is also found that a variation of the sequence distribution away from a purely random structure can dramatically effect the ability of the copolymer to modify the interface. As most polymers which are not block nor alternating are termed ‘random’, this differentiation may have an effect on experimental studies of ‘random’ copolymers as compatibilizers in polymer blends.
Morphology Characterization in Multicomponent Polymer Systems using Scanning Probe Microscopy
Authors: Viswanathan Ravi , Tian Jing , Marr David W.M. 
Published: April 2011

ABSTRACTA newly available scanning probe microscopy, phase imaging, has been used to image polyethylene (PE) blends and composites. By providing not only a topographical map of the surface but also information on material properties, this technique has allowed ready identification of individual components within the mixtures investigated.
3D Micro-Tomographic imaging and Quantitative Morphometry for the Nondestructive Evaluation of Porous Biomaterials
Authors: Müller R. , Matter S. , Neuenschwander P. , Suter U. W. , Rüegsegger P. 
Published: April 2011

ABSTRACTMicro-computed tomography (μCT) is a new and emerging technique for the nondestructive assessment and analysis of the three-dimensional trabecular bone architecture. The applications of μCT with respect to the analysis of bone are manyfold. Nevertheless, it also holds high promise for the microstructural measurement and analysis of porous biomaterials. For the purpose of the study, a desk-top μCT providing a nominal isotropie resolution of 14 μm was used. Since the polymeric material has a very low X-ray absorption coefficient, the scaffolds were stained prior to measurement using a commercial X-ray contrast agent. This allowed not only to acquire important microstructural features of the diree-dimensional scaffold but also to compute standard structural indices such as BV/TV, BS/BV, Tb.N, Tb.Th, Tb.Sp and the degree of anisotropy (DA) using mean intercept length measurements. The preliminary results show that different types of scaffolds can be distinguished both qualitatively (visualization) and quantitatively (morphometry) provided an adequate X-ray staining technique is used. It can be concluded that, in the future, μCT may be of considerable help in basic as well as in applied research and development.
Molecular and Textural Ordering of Thermotropic Polymers in Shear Flow
Authors: Romo-Uribe A , Mathers P. T. , Chaffee K. P. , Han C.D 
Published: April 2011

ABSTRACTThe texture and microstructural order present in mesomorphic polymers and their relation to their macroscopic behavior has been investigated using rheological, optical and dynamic scattering (WAXS and SALS) experiments. Shear orientation is observed under constant rate-of-deformation conditions where this orientation is always parallel to the flow direction. However, the high degree of orientation suggested by optical and SALS measurements is not reflected in the degree of molecular order observed in WAXS experiments. After cessation of flow, a rapid relaxation of stress is observed, while only little microstructural relaxation is found; i.e., the state of orientation is very stable
Investigation of the Altered Layer on Ancient Chinese Bronze Mirrors and Model High-Tin Bronzes
Authors: Taube Michelle , King Alexander H. , Thomas Chase W. 
Published: April 2011

ABSTRACTMany ancient Chinese bronze mirrors have a smooth patina. An ingress of corrosion to a depth of approximately 100 μm is found beneath the patina. The corrosion selectively replaces the Cu-rich α phase leaving the Sn-rich σ phase intact. Previous work by x-ray diffraction has shown that the a-phase replacement product is poorly crystallized or nanocrystalline SnO2. Transmission electron microscopy was employed to further characterize the replacement product in both ancient mirror and replication samples. Nanocrystalline SnO, in the form of small spheroids has been found. Remnants of an original alloy phase appear to be interspersed with the tin oxide.
An Investigation of the Antimony-Containing Minerals used by the Romans to Prepare Opaque Colored Glasses
Authors: Mass Jennifer L. , Stone Richard E. , Wypyski Mark T. 
Published: April 2011

ABSTRACTRoman colored opaque vessel glasses and mosaic tesserae were examined using energy dispersive X-ray analysis, wavelength dispersive X-ray analysis, and scanning electron microscopy in order to identify the origins of the antimony-based glass opacifying agents used in the Roman period. Bindheimite and stibnite were considered as mineralogical sources of antimony, and antimonial litharge was investigated as a metallurgical source of antimony. The refining of antimonial silver ores was discussed as a source for antimonial litharge in the Roman period. The morphologies of the antimonate crystallites, their distributions, and the observed correlations of lead to antimony in the glasses indicated that roasted stibnite was the antimony source for the white and blue opaque glasses and antimonial litharge was the antimony source for the yellow and green opaque glasses. Opaque yellow Roman glasses were found to contain a mixture of clastic, subhedral, and euhedral lead pyroantimonate (Pb2Sb2O7) particles. The euhedral crystallites are a rhombohedral modification of Pb2Sb2O7that is formed above 900 °C.
Use of Coupled Passivants and Consolidants on Calcite Mineral Surfaces
Authors: Nagy Kathryn L. , Cygan Randall T. , Scotto Cathy S. , Jeffrey Brinker C. , Ashley Carol S. 
Published: April 2011

ABSTRACTDeterioration of monuments, buildings, and works of art constructed of carbonate-based stone potentially can be arrested by applying a combination of chemical passivants and consolidants that prevent hydrolytic attack and mechanical weakening. We used molecular modeling and laboratory synthesis to develop an improved passivating agent for the calcite mineral surface based on binding strength and molecular packing density. The effectiveness of the passivating agent with and without a linked outer layer of consolidant against chemical weathering was determined through leaching tests conducted with a pH-stat apparatus at pH 5 and 25°C. For the range of molecules considered, modeling results indicate that the strongest-binding passivant is the trimethoxy dianionic form of silylalkylaminocarboxylate (SAAC). The same form of silylal-kylphosphonate (SAP) is the second strongest binder and the trisilanol neutral form of aminoethylaminopropylsilane (AEAPS) is ranked third. Short-term leaching tests on calcite powders coated with the trisilanol derivative of SAAC, the triethoxy neutral form of SAP, and the trimethoxy neutral form of AEAPS show that the passivant alone does not significantly slow the dissolution rate. However, all passivants when linked to the sol consolidant result in decreased rates. Combined AEAPS plus consolidant results in a coating that performs better than the commercial product Conservare® OH and at least as well as Conservare® H. The modeling results indicate that there may be a threshold binding energy for the passivant above which the dissolution rate of calcite is actually enhanced. More strongly-binding passivants may aid in the dissolution mechanism or dissociate in aqueous solution exposing the calcite surface to water.
A Study of the Role of Heterogeneities in the Initial Stages of Corrosion of Glazes Using Dynamic Imaging Microellipsometry (DIM)
Authors: McCarthy B.E. , Vandiver P.B. , Kruger J. 
Published: April 2011

ABSTRACTCommon processes used in glazed ceramic production often result in a glaze with a heterogeneous microstructure. Heterogeneities may be due to residual batch materials, intentionally added colorants and opacifiers and/or the products of devitrification and phase separation. To study the effect of heterogeneities in the corrosion process, dynamic imaging microellipsometry was used in-situ in aqueous solutions to measure spatially and temporally resolved changes in the surface of glasses (model glazes). The measurements showed increased durability near inclusions. Residual stress fields surrounding the heterogeneities influenced the results. Decoupling of chemical and mechanical factors causing this increased durability was not possible.
Chemical Composition and Microchemistry of “Free Galloping Horse” Bronze Punic Coins
Authors: Ingo G.M. , Manfredi L-I. , Caroli S. , Bultrini G. , Chiozzini G. , Femmine P. Delle 
Published: April 2011

ABSTRACTA large group of the so called “free galloping horse” bronze Punic coins, that is the most common series largely diffused in the Mediterranean basin, has been found during the archaeological excavation at Tharros (western Sardinia, Italy). Forty-seven coins have been studied in order to determine the chemical composition and the microchemical structure of the copper alloys used by Punies for the coinage of this series and to gain further information about the metal ores used to produce the metals. The results have shown that copper, tin, iron, silver, antimony, lead, zinc and arsenic vary significantly thus indicating different trends in the alloys production. The content of the major and minor elements has also indicated that Punic metallurgists controlled only the content of some elements to within quite narrow limits and when deliberate adding was used just to increase the metal to fill the mould, as might sometimes be the case with the addition of lead instead of the more expensive tin.
Quantitative Analysis of Displacement at 90° Domain Boundaries In BaTiO3 and PbTiO3
Authors: Ross Frances M. , Kilaas Roar , Snoeck Etienne , Hÿtch Martin , Thorel Alain , Normand Laurent 
Published: April 2011

ABSTRACTIn this paper we discuss the measurement of long range displacement fields associated with 90° domain boundaries in the ferroelectric ceramics BaTiO3 and PbTiO3. We have calculated displacement fields from high resolution lattice images by two techniques: firstly, measuring the positions of peaks in the images, and secondly, using a geometric phase analysis technique to magnify small lattice distortions. We describe the results and consider the complementary use of Fresnel contrast analysis to characterize local strain and electric fields near the boundaries.
Creation of Nanocrystals Via a Tip-Induced Solid-Solid Transformation
Authors: Zhang Jian , Liu Jie , Huang Jinlin , Kim Philip , Lieber Charles M. 
Published: April 2011

ABSTRACTScanning tunneling microscopy (STM) is a powerful tool for nanoscale research since it can both create and probe the properties of nanostructures. We have used STM to create T-phase TaSe2 nanocrystals embedded in H-phase TaSe2 through a tip-induced solid-solid phase transition at liquid He temperature. Atomic-resolution images have been used to develop a structural model to understand this solid-solid phase transformation. Furthermore, STM studies of the charge density wave (CDW) state in the T-TaSe2 nanocrystals have been used to address CDW physics in finite dimensions.
The Conversion of Czochralski Silicon from P-Type to N-Type by Hydrogen Plasma Enhanced Thermal Donor Formation
Authors: Job R. , Borchert D. , Bumay Y. A. , Fahrner W. R. , Grabosch G. , Khorunzhii I. A. , Ulyashin A. G. 
Published: April 2011

ABSTRACTOur experiments show a hydrogen plasma assisted creation of p-n junctions in p-type Cz silicon due to a hydrogen enhanced thermal donor (TD) formation at temperatures ≤450 °C. Applying DC or HF plasma treatments a conversion of p-type into n-type Cz silicon by TD formation occurs. One can distinguish one step processes (p-n junction formation appears just after the plasma exposure) and two step processes (p-n junction formation requires subsequent post hydrogenation annealing). The samples are studied by depth resolved spreading resistance probe (SRP), capacitance-voltage (CV) and Hall measurements. For the one step processes a kinetic model for hydrogen enhanced TD formation is presented.
Diffusion of Silicon Interstitials in thin Silicon Films on Insulator in Neutral and Oxidising Annealing Ambients
Authors: Silvestre Guénolé C.M. 
Published: April 2011

ABSTRACTSilicon-On-Insulator (SOI) materials have emerged as a very promising technology for the fabrication of high performance integrated circuits since they offer significant improvement to device performance. Thin silicon layers of good crystalline quality are now widely available on buried oxide layers of various thicknesses with good insulating properties. However, the SOI structure is quite different from that of bulk silicon. This paper will discuss a study of point-defect diffusion and recombination in thin silicon layers during high temperature annealing treatment through the investigation of stacking-fault growth kinetics. The use of capping layers such as nitride, thin thermal oxide and thick deposited oxide outlines the diffusion mechanisms of interstitials in the SOI structure. It also shows that the buried oxide layer is a very good barrier to the diffusion of point defects and that excess silicon interstitials may be reincorporated at the top interface with the thermal oxide through the formation of SiO species. Finally, from the experimental values of the activation energies for the growth and the shrinkage of stacking-faults, the energy of interstitial creation is evaluated to be 2.6 eV, the energy for interstitial migration to be 1.8 eV and the energy of interstitial generation during oxidation to be 0.2 eV.
Vacancies and Interstitial Atoms in Irradiated Silicon
Authors: Ehrhart P. , Zillgen H. 
Published: April 2011

ABSTRACTDifferently doped Si-wafers were irradiated with 2.5MeV electrons and subsequently investigated by X-ray diffraction methods. We show that a high concentration of defects (>1016 cm−3) can be frozen in at 4K and that a large fraction of the defects is stabilized in the form of close Frenkel pairs. These Frenkel pairs are characterized by the nearly perfect cancellation of the long-range displacement fields of the interstitial atom and the vacancy. We discuss the absolute size of these displacements as well as the introduction rate of the defects, which is of the order of Σ = 1cm−1. Similar results are obtained for weakly doped Cz-Si or FZ-Si and for degenerate p-type Si(B) and n-type Si(As), i.e., the results are independent of the oxygen content of the samples and of the position of the Fermi level. The high defect introduction rates are at variance with the results of electrical and EPR investigations and indicate that these methods detect only a few percent of the total defect concentration which is produced and frozen in at 4K. The consequences for the understanding of the defect production in Si and for the assumption of an athermal migration of interstitial atoms are discussed. In addition we compare the defect patterns observed after 4K irradiation to those observed after room-temperature irradiations and discuss the thermally activated defect reactions up to the final annealing at 1000K.
Extracting Information from a Supercell Calculation
Authors: Harrison W. A. 
Published: April 2011

ABSTRACTA number of corrections must be made to a first-principles defect supercell calculation if the results are to be of use in calculating properties of isolated defects. These are illustrated for a tetrahedral self-interstitial in silicon, which places two electrons in the conduction band. One correction arises from the familiar Coulomb enhancement of the gap relative to local-density-approximation (LDA) calculations. The second is for the capture of these electrons in a double donor state. The third arises from the extra kinetic energy of the electrons due to their partial filling of the conduction band for a finite-sized supercell. The fourth is the partial occupation of the defect resonance, lowering the kinetic energy but increasing the Coulomb energy. A model is introduced which allows estimates of each of these corrections, with parameters which can be tuned to LDA supercell calculations. It allows then prediction of a wide range of properties dependent upon the defect in question.