bluuebunny/crossref_metadata_2025_split huggingface dataset:
Survey of Eutectic Systems as Potential Intermetallic Matrix Composites for High Temperature Application
Authors: Mazdiyasni S. , Miracle D. B. 
Published: March 2011

AbstractThe lack of low-temperature damage tolerance along with the desire to achieve lower densities and higher creep strengths over monolithic intermetallic materials, has sparked significant interest in the research community for the development of an intermetallic matrix composite suitable for high temperature structural applications. Eutectic systems are desirable as composites due to the inherent thermodynamic stability between matrix and reinforcement. It also allows the opportunity of controlling the microstructure by control of solidification conditions. This paper presents a qualitative examination of the toughness behavior of the Cr-Cr2Zr, Cr-Cr2Hf, Cr-Cr2Ta, Cr-Cr3Si, Ta-Cr2Ta, and Ta-Ta5Si eutectics. The evaluation is based on microcracking from microhardness indentations and fracture appearance. Relative oxidation resistance at 800°C and 1200°C is also presented.
Dislocation Morphologies in TiB2/NiAl
Authors: Wang L. , Arsenault R. J. 
Published: March 2011

AbstractThe addition of 20 volume percent titanium diboride in particulate form (1-3 μm) to nickel aluminide (TiB2/NiAl) results in a twofold increase in the high temperature strength of NiAl. Theories that have been proposed to account for the high temperature strength of discontinuous reinforced metal matrix composites can not be adequately used as a basis to explain the observed strengthening.An investigation was undertaken of NiAl, 10 V% TiB2/NiAl and 20 V% TiB2/NiAl in the annealed condition and after deformation, allowed to cool slowly. There is a low dislocation density in the annealed samples and the dislocation density did increase slightly as a result of deformation. However, deformation did produce some intriguing dislocation arrangements; for example, it was found that there was a high dislocation density within the TiB2 in the deformed higher volume fraction composites and the dislocation density within NiAl matrix was not uniform.
The High Temperature Behaviour of TiAl Containing Carbide Reinforcements
Authors: Rösler J. , Valencia J. J. , Levi C. G. , Evans A. G. , Mehrabian R. 
Published: March 2011

AbstractThe mechanical behaviour of γ-TiAl reinforced with Ti2AIC platelets is investigated in the temperature range between 293K and 1255K. Comparison with the particle-free material of same matrix composition reveals a pronounced strengthening effect of the platelike reinforcements up to about 1000K. However, under creep loading the composite is remarkably weak. It is shown that this weakness is caused by diffusional creep along the particle/matrix interface. Modelling of this process indicates that the dimensions of the Ti2AlC particles (thickness d=lμm, length l=20μm) are too small to avoid this unwanted deformation mechanism. It is concluded that thicknesses well above 10±m are needed to maintain reinforcement strengthening at high temperature in this system.
Strength and Toughness of Single-Phase and Dual-Phase High-Temperature Intermetallics
Authors: Bruemmer Stephen M. , Brimhall John L. , Henager Charles H. 
Published: March 2011

AbstractThe strength and toughness of several high-temperature beryllium-niobium (Be12Nb and Be17Nb2) and iridium-niobium (lr3Nb) intermetallic compounds have been evaluated. Materials were prepared by high-rate sputter deposition and characterized by x-ray diffraction and analytical electron microscopy before and after heat treatment. As-sputtered microstructures were varied from amorphous to microcrystalline by control of substrate temperature. Grain size, degree of order, and second-phase distribution were modified by subsequent heat treatment. Strength as a function of temperature was assessed by hot hardness tests and toughness estimated from indentation-induced crack lengths. Intermetallics exhibited very high strength and low toughness up to temperatures of ˜1000 C. Mechanical behavior was a direct function of the microstructural parameters including matrix phase composition, second phase distribution, and degree of order.
Effect of XD™ TiB2 Volume Fraction on the Microstructure of a Cast Near-gamma titanium aluminide alloy
Authors: Larsen Donald E. , kampe Stephen , Christodoulou Leo 
Published: March 2011

AbstractTiB2 particulate levels ranging from 0.1 to 4.6 volume percent were incorporhted into the near-gamma titanium aluminide alloy Ti-47.5Al-2Nb-2Mn (at%) via the XD™ process. Material was prepared by Vacuum ArcRemelting (VAR) followed by investment casting into cylindrical bars. Results show that grain refinement occurs in alloys with XD™ TiB additions equal to or greater than 1.0 volume percent. Alloys with ad itions of less than 1.0 volume percent TiB2 contained boride phases having lacey and blocky morphologies. Alloys with additions of 1.0 volume percent TiB2 or greater contained needle shaped borides, blocky equiaxed borides and lacey borides. Determination of boride phase morphology, boride type and microstructural response were determined by backscattep electron imaging (BEI), electron microprobe analysis (EMPA), X-ray diffraction (XRD) and optical metallography.
Innovative Processing Techniques for Intermetallic Matrix Composites
Authors: Stoloff N. S. , Alman D. E. 
Published: March 2011

AbstractAlthough intermetallics based upon aluminum or silicon tend to have a very attractive combination of low density and excellent oxidation resistance, they suffer from lack of adequate creep strength and, in most cases, from inadequate ductility and toughness. It has been recognized for several years that an approach which could simultaneously solve both problems, without degrading other properties, is to utilize the intermetallics as matrices for composite materials. The consequence has been an explosion of interest in two-phase intermetallicbased alloys, as is manifested in the current symposium.
A Study of the Volume Fraction, temperature and Pressure Dependence of the Resistivity in a Ceramic–Polymer Composite using a General Effective media Equation
Authors: McLachlan David S. , Blaszkiewics Michael , Yoshikawa Shoko , Newnham Robert E. 
Published: March 2011

ABSTRACTA General Effective Media (GEM) equation is used to quantitatively describe the resistivity of an Fe304-eccogel composite system as a function of the relative volume fractions. The two percolation morphology parameters (øc and t) characterise the microstructure. Preliminary models, also based on the GEM equation, are used to describe the positive temperature coefficient of resistivity (PTC) and the piezoresistivity (uniaxial pressure) of the composite when the composition is near the percolation threshold.
Microwave Properties of Non-Percolating Metal-Insulator Composites
Authors: Jacobs I.S. , Patchen H.J. , Miller S.A. , Rachford F.J. , Hanson J.O. 
Published: March 2011

ABSTRACTPermittivity and permeability have been studied at microwave frequencies (1 to 20 GHz) on artificial dielectrics of metal particles randomly loaded in a polymer up to 40 vol%. Ni-Cr alloy powder (∼1 to 37 μm) in various size fractions was prepared by gas-water atomization, providing an oxide coating for interparticle isolation. The alloy is ferromagnetic below 165 K, enabling a magnetic measure of volume loading. The complex permeability results are in very good agreement with calculations of induced magnetic dipole effects as functions of frequency and particle diameter. Permittivity results are independent of particle size and essentially constant with frequency. When compared with a highly successful effective spherical cluster model and a well-founded empirical curve, the present alloy powder exhibits a residual upward deviation attributed to nonspherical morphology. In sum, the microwave electromagnetic behavior of such non-percolating composites is rather well understood.
The Formation of New Critical System by Electric Breakdown in Percolation System
Authors: Garanov V.A. , Kalachev A.A. , Karimov A.M. , Lagar´kov A.N. , Matitsin S.M. , Pakhomov A.B. , Peregood B.P. , Sarychev A.K. , Vinogradov A.P. , Virnik A.M. 
Published: March 2011

ABSTRACTA new way of obtaining binary composite materials having some properties of the critical percolation system is presented..These materials can be obtained by high-density current action on an initially well conducting mixture.This action destroys part of contacts between adjacent conducting granules bringing the system to the quasi-critical state.It is shown that quasi-critical s stems may have high values of dielectric constant ε′ ∼ 102-106 101 in the frequency range 0<f<1010Hz.Formation and dielectric properties of the systems are studied both by computer simulation and experi mentally.
The Response of Two-Dimensional Granular Superconducting Films to Light
Authors: Culbertson J. C. , Strom U. , Wolf S. A. 
Published: March 2011

ABSTRACTWe have examined the photoresponse of two-dimensional granular superconducting films of high Tc superconductors (Y-Ba-Cu-O). We see evidence for the existence of a twodimensional Kosterlitz-Thouless transition. The photoresponse and resistance have been measured as a functions of temperature, excitation power, bias current, and photon energy. The response to photons having energies above and below the superconducting energy gap(s) has been measured. Photoresponse features have been observed that are not explainable in terms of a conventional phonon bolometric mechanism. Comparison will be made with similar observations made on low temperature superconducting films (NbN-BN).
Phase Transitions in Dissipative Josephson Chains
Authors: Bobbert P.A. , Fazio R. , Schon Gerd , Zimanyi GT. 
Published: March 2011

ABSTRACTWe study the zero temperature phase transitions of a chain of Josephson junctions, taking into account the quantum fluctuations due to the charging energy and the effects of an Ohmic dissipation. We map the problem onto a generalized Coulomb gas model, which then is transformed into a sine-Gordon field theory. Apart from the expected dipole unbinding transition, which describes a transition between globally superconducting and resistive behavior, we find a quadrupole unbinding transition at a critical strength of the dissipation. This transition separates two superconducting states characterized by different local properties.
Non-Ohmic Normal State Behavior and the Onset of Global Superconductivity in Partially Annealed Quench–Condensed Films of Tin
Authors: Shiffman Carl A. , Markiewicz Robert S. , Ho Men 
Published: March 2011

ABSTRACTFilms of tin condensed onto 4K pyrex substrates can be driven from “insulating” (i.e. dR/dT < 0) to superconducting behavior by low temperature annealing. Global superconductivity occurs when the normul state sheet resistance, R□, shrinks to a value very near R□≡ h/4ea, as in experiments where R□is changed by increasing the film thickness. When R□> R□, conduction is decidedly non-ohmic, with R□(T,V) = R□(T) + R1(T)exp(−m(T)|V|).
Optical Properties of Granular Materials: How to Model Coatings for Energy-Efficient Windows
Authors: Granqvist C.G. 
Published: March 2011

ABSTRACTI discuss coatings for energy efficient windows of several different kinds with a view to the possibility of modelling their optical properties by effective medium theory. Special attention is given to spectrally selective noble-metal-based coatings with induced transmission due to voids, angular selective metal coatings with oblique columnar microstructure, and tentative theoretical descriptions of chromogenic materials having dynamic radiative properties.
Surface Impedance and Granularity in Superconducting Cuprates
Authors: Halbritter J. 
Published: March 2011

ABSTRACTThe rf residual surface resistance Rres is an important figure of merit for superconducting microwave devices and for establishing the homogeneity of superconducting surfaces. In granular superconductors not only are high residual rf surface resistance values Rres observed, but also strong field dependencies of Rres(T,ω, Hrf) and the penetraton depth λres(T, ω, Hrf) are encountered even at very low field levels (of order 1 Oe). These observations can be explained in terms of granularity consisting of weak links and of insulating interfaces, which provide additional degrees of freedom due to fluxoid motion and electromagnetic strip line modes. These degrees of freedom cause additional interaction mechanisms with applied rf fields.
A Chord Distribution Description of Porous Glass
Authors: Lin M. Y. , Sinha S. K. 
Published: March 2011

ABSTRACTSmall angle neutron scattering data of Vycor is analyzed using a chord distribution model describing the microporous structure. In addition, the same model is applied in interpreting the data taken when capillary condensation takes place in the porous medium. In both cases, the results are in good agreement with other measurements, and shows a promising potential in describing such a bicontinuous system.
Monte Carlo Simulations of Effective Diffusivities in Three—Dimensional Pore Structures
Authors: Reyes Sebastian C. , Iglesia Enrique , Chiew Yee C. 
Published: March 2011

ABSTRACTA hybrid discrete/continuum Monte Carlo technique combining random walk simulations with first passage time (FPT) concepts is developed here in order to estimate diffusion properties of randomly-assembled sintered porous structures. This work combines the creation of realistic porous solid structures with controlled pore size, shape, and tortuosity features with the application of an efficient algorithm for calculating effective diffusivities in all diffusion regimes (Knudsen, transition, and molecular). The hybrid simulation technique consists of creating a “protective” boundary layer surrounding solid surfaces within which discrete random motion simulations are performed while continuum FPT results are used in the remaining pore space. The boundary layer thickness reflects a characteristic length scale, of the order of a few mean free paths, over which the FPT approximation breaks down. This procedure significantly reduces the computations required to cover statistically representative regions of the porous structure,a serious shortcoming in previous studies of gas diffusion through porous solids; it leads to effective diffusivity estimates that are in excellent agreement with experimental measurements.
Melting and Thermal Characteristics of Small Granular Particles
Authors: Sheng Ping , Zhou Min-Yao 
Published: March 2011

ABSTRACTWe present results of theoretical calculations on the thermal characteristics of small granular particles. By using the selfconsistent Einstein model with a Morse interaction potential, it is shown that Debye temperature drops significantly for particle sizes below 50Å, a phenomenon observed experimentally. Melting temperature of small particles is calculated using a generalized Lennard-Jones-Devonshire theory. Depression of the melting point by as much as 60% is obtained from particles <10Å in size. Consideration of the constraining effect of the elastic matrix show that under the condition of tight coupling with the matrix the melting point of small particles may be significantly enhanced.
Preparation and Properties of Co/SiO2 and Co3O4/SiO2 Composites
Authors: Win W. , Logothetis E. M. , Soltis R. E. , Plummer H. K. , Wenger L. E. 
Published: March 2011

ABSTRACTFilms of Co/SiO2 composites were prepared by sequential sputtering from Co and SiO2 targets in Ar. As-grown films as well as films annealed in H2/N2 atmospheres consist of hcp Co particles of uniform size embedded in the SiO2 matrix. The measured optical absorption spectra of these composites are consistent with the Maxwell-Garnett theory except for the absence of the predicted structure that arises from the interband transitions of cobalt. Composites consisting of semiconducting Co3 O4 particles embedded in SiO2 were prepared by post-growth annealing of Co/SiO2 films in air. The optical properties of these composites were found to be comparable to those of CO3O4.
Preparation and Mechanical Properties of Ultrafine Grained Metals
Authors: Gunther B. , Baalmann A. , Weiss H. 
Published: March 2011

ABSTRACTUltrafine—grained polycrystalline metallic components (Cu, Au, Fe) have been prepared by means of the inert gas evaporation technique combined with an integrated uniaxial cold compaction device. The average grain sizes ranaed typically from 20 nm to about 100 nm. The microstructure and Imourity content of the as-pressed samples have been investigated by means of TEM and AES, respectively. The yield strength of ultrafine (30 nm) grained Cu specimens obtained in tensile tests compares well with respective values for heavily cold—worked coarse grained copper. Al slight heat treatment (150ºC/30min) improves the strain—to—fracture at slightly reduced yield strength values. The results are discussed within the picture of two concurrent processes determining the strength of ultrafine grained metals: Coble creep vs. grain boundary strengthening effect.
The Optical Properties of Semi-Continuous Metal Films: A Scaling Based Model
Authors: Yagil Y. , Yosefin M. , Bergman D. J. , Deutscher G. 
Published: March 2011

ABSTRACTWe present a calculation of the optical properties of thin semi-continuous metal films near the percolative metal-insulator transition. The model is based on scaling assumptions, reflecting the fractal nature of these films. The film is divided into small squares of linear size L and the local complex conductivity of each square is calculated, using finite size scaling arguments and taking into account both ohmic resistance within the metallic clusters and intercluster capacitance. The size L, over which the finite size scaling is done, is related to the optical frequency by the anomalous diffusion relation, i.e. L(ω) α ωl/(2+θ). In this calculation two types of conductivities are found : good ones for the ‘metallic’ squares, showing that large clusters are present within these squares, and poor conductivities for ‘dielectric’ squares, where only small clusters are present. Moreover, the ‘metallic’ and ‘dielectric’ squares are not identical, thus a certain distribution of each type has to be considered. The width of the distribution is quite large close to the percolation threshold and decreases to zero when the film becomes homogeneous. The optical properties of the whole sample are obtained by summing the contribution from all squares, using a wide bimodal distribution function. Comparison with recent experimental results shows good agreement between this model and the experimental data.
A Quantitative Study of Cavity Evolution in An Al-Cu-Zr Alloy
Authors: Zhao Xiaoyu , Langdon Terence G. 
Published: March 2011

ABSTRACTExperiments were conducted on a superplastic aluminum-based alloy containing 6% Cu and 0.5% Zr. Specimens were pulled in tension under selected experimental conditions and then polished and examined with an optical microscope connected through a video camera to an image monitor and a personal computer. A software package was used to provide quantitative information on the cavity morphologies including the number of cavities in a selected area, their size, their deviation from a circle, and the orientation of their longest length with respect to the tensile axis. Results are presented showing the change in cavity morphology with elongation and the effect of testing at different strain rates.
The Superplastic m-δ Relationships of the T10 Steel
Authors: Liu Chin , Wei Wong , Fu Liu Wan 
Published: March 2011

ABSTRACTAt 700°C, with strain rates (έ) of 0.02, 0.05 and 0.08 min−1, the superplastic m-δ curves of T10 steel determined were all of the type (the general type). Their Values of rr (0.241 → 0.252 → 0.267), mL (0288 → 0.241 → 0.252 ),mF (0236 → 0.251 → 0.268), δL(38→. 535 →.58%), and δF (84.7 → 92 → 99%) all increased with increases in value. At the same temperature with έ =0.1 min−1, an ascending type of curve, mL=mwn = mo(=0.245)<mx (=.0.249), δo (=0)= δL > δx (=94%) was obtained from the transformation of δL and mL into the δF and mL of the general type of curve. Similar results have been obtained at 730°C.At 600°,650°, 700° and 730°C, with έ =0.05 min−1 the same general type of curves were obtained. Their values of mo. (0.213 → 0.230 → 0.252 → 0296), mL (0.19 5 → 0.208 → 0.241 → 0.256 ).mF (0.204 → 0.234 → 0.251 → 0.280). δL (44 → 49 → 53.5 → 63.5%)and δF (77 → 81 → 117 percnt) increased with increases in temperature. For the same strain rate, while at 780°C, an ascending type of curve, mL.= mmis = mo (= 0.198) < mF (0.236).δo (=o) = δL < δx (=73%)was obtained from the transformation of the general type of curve in the same way as mentioned above.The shape constants, C values, which vary with strain have been calculated.Symbols: Refer to the List of Symbols.
Influence of Specimen Notices on the Superplastic m-δ Relationship of Zn-Ni-Mg Alloy
Authors: Liu Chin , Jin Tao 
Published: March 2011

ABSTRACTWith AM/Ao = 1, the superplastic m- δ curves of Zn-Ni-Mg alloy have been studied. When T=220°C and έ (initial)=1.33×10−2 min−1, the curve was of the type. It was transformed into the mL =mmin =mo<mF,δL=δL<εF type of curve, when T=200°–230°C and έ (initial)=3.33×10−2 min−1 and further transformed the type at 240°–250°C with the same strain rate.With AN/Ao<1 and >0.595, T=230°C and έ (initial)=3.33×10−2 min−1 the curves were all of the mL=mmax =mo <mF, δ.(=O)= δL < δF type. The δF values increased with increase in AN/Ao value. The effect mainly reflected on the CF value and the CL m-δ equation can be expressed to account for the notch effect as follows:where and AN/Ao < 1 and > 0.595.Symbols: Refer to the List of Symbols.
Superplastic Deformation of YBa2Cu3O7−x in a Superplastic Metal Matrix
Authors: Moreno J. Emilio , Torres-Villasefor G. 
Published: March 2011

ABSTRACTThe new class of high-transition-temperature ceramic superconductors (e.g. Y-Ba-Cu-O) show a fine grain size polycrystalline structure, similar to that shown by the superplastic metals. The material behaves in a brittle manner with a strain to fracture below 0.5 % at room temperature. One of the reasons for this mechanical behavior is that the grain boundaries are easily separated when a stress is applied. It was found in this work that a deformation of the superconductor ceramic (scc) in superplastic metal (spin) matrix reduces the separation of the grain boundaries in such materials so that they can be deformed at room temperature. The spin matrixes used in this work were Zn-Cd, Bi-Sn and Cd-Sn. It was found that the highest the yield point of the matrix the highest the deformation induced in the scc. The Cd-Zn alloy was the most effective in avoiding the separation of the grain boundaries during the deformation of a composite formed by a cylinder of scc embedded in a spin matrix. Meissner effect was observed in the scc, after more than 160 % of plastic deformation. SEM observations show that deformation takes place by grain boundary sliding and some grain refinement was observed.
Superplasticity of Non-Oxide Ceramics
Authors: Wakai Fumihiro , Kodama Yasuharu , Sakaguchi Shuji , Murayama Norimitu , Izaki Kansei , Niihara Koichi 
Published: March 2011

ABSTRACTSuperplasticity is a mode of deformation for fine-grained polycrystalline solids at elevated temperatures: included are metals, ionic polycrystals (e.g. oxides) and covalent polycrystals (e.g. non-oxide ceramics). Plastic deformation of covalent crystals by dislocation glide is not easy because of their high Peierls force. This paper describes high ductilities in Si3N4 and SiC, and also reports superplastic elongations in Si3N4/SiC composite.Fine-grained Si3N4/SiC composites (20 wt% SiC) were fabricated by hot-pressing amorphous Si-C-N powder with 6 wt% Y2O3 and 2 wt% A12O3 as sintering aids. The composites were composed of equiaxed grains (<200 nm) and elongated grains. A composite exhibited a superplastic elongation larger than 150 % at 1600 °C and at an initial strain rate of 4 × 10−5 s−1. The superplasticity of the composite is probably related to the presence of an intergranular liquid phase.