bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fatigue of Extruded Steel/Nial Composites
Authors: Bannister M. K. , Spearing S. M. , Löfvander J. P. A. , Graef M. De 
Published: March 2011

ABSTRACTFatigue tests were performed on a novel, extruded, stainless steel/NiAl composite having good impact and tensile properties. A high fatigue limit was observed to occur at approximately 67% of the σUTS. The fracture surface showed a distinct change in morphology between the fatigued and fast fracture areas and the formation and growth of microcracks was postulated as the initial fatigue mechanism. The microcrack development was monitored by intermittent measurement of the elastic modulus and associated hysteresis. Microstructural characterization by means of SEM, TEM and EDS revealed the existence of approximately 100nm diameter Al2O3 particles decorating the interface between the NiAl and the stainless steel tubes.
Oxidation of Powder Processed Nial and Nial/Tib2 Composites
Authors: Korinko P. S. , Alman D. E. , Stoloff N. S. , Duquette D. J. 
Published: March 2011

ABSTRACTNiAl and NiAl/TiB2 composites were tested in air at 800, 1000, and 1200°C. The oxidation resistance of the composites depends on the fabrication route, and subsequently on the reinforcement phase morphology and distribution. The oxidation resistance of NiAl reinforced with large TiB2 particles was found to decrease with increasing TiB2 content. NiAl reinforced with large TiB2 particles was completely oxidized at 1200°C after a 100 hour exposure.
The Structure and Properties of MoSi2-Mo5Si3 Composites
Authors: Kung H. , Mason D. P. , Basu A. , Chang H. , Aken D. C. Van , Ghosh A. K. , Gibala R. 
Published: March 2011

ABSTRACTThe addition of Mo5Si3 as a reinforcing second phase in a MoSi2 matrix has been investigated for possible high temperature strengthening effects. MoSi2 with up to 45 vol % Mo5Si3 was fabricated using powder metallurgy (PM) and arc-casting (AC) techniques. Effects of processing routes, which result in different microstructures, on their mechanical properties are given. PM composites, which have an equiaxed microstructure, exhibit a limited increase in hardness. Higher hardnesses are observed in script-structured AC eutectics and Er-modifiedeutectics throughout the temperatures studied (25–1300°C). Crack propagation paths induced by indentation show long transphase cracks in the AC materials vs short intergranular and interphase cracks in the PM composites at high temperatures.Transmission electron microscopy discloses that the interface in the AC composites has a low-index orientation relationship between the two phases and shows regularly faceted interfacial structures, while planar interfaces are found in the PM composites. These observations suggest the interface is stronger and lower in energy in the AC composites, which is consistent with the higher hardness values and long transphase cracks observed.Dislocation analysis shows the presence of ordinary dislocations (<100>, <110> and 1/2<111>) in MoSi2 in the as-fabricated composites. These types of dislocation are also responsible for the high temperature plastic deformation in compression in both the monolithic MoSi2 and the composites. <331> types of dislocation are only found in MoSi2 either near the interface of the AC composites or in materials deformed below 1000°C.
Electron Microscopy Studies Of Mo5Si3-MOSi2 Eutectic Composites Modified By Erbium Additions
Authors: Mason D. P. , Aken D. C. Van , Mansfield J. F. 
Published: March 2011

ABSTRACTErbium additions to MO5Si3-MoSi2 eutectic composites have been investigated in an effort to reduce oxygen impurity levels found in the MoSi2 starting powders. Additions of 0.35 atomic percent Er were found to refine the script lamellar microstructure and increase the hardness of the composite as compared with the unmodified material. This increase in hardness was maintained over the temperature range 25°C to 1300°C. Oxygen rich Er particles have been observed in the Er-modified material suggesting that Er has acted as a gettering agent for oxygen. An intermetallic phase Er2Mo3Si4was also observed in the Er-treated material. The character of this phase was determined by convergent beam electron diffraction (CBED), wavelength dispersive spectroscopy (WDS) and X-ray dispersive spectroscopy (XEDS). The particles of Er2Mo3Si4 were found to be heavily faulted which caused a reduction in the experimental diffraction symmetries. Thus, ambiguities arose during CBED analysis. Therefore, a standard sample of Er2Mo3Si4 was prepared and used to aid in the identification of the faulted particles.
Interfacial Shear Behavior of Two Titanium-Based SCS-6 Model Composites
Authors: Roman I. , Jero P. D. 
Published: March 2011

ABSTRACTSingle fiber push-out and push-back tests combined with acoustic response monitoring were used to examine the interfacial behavior in two titanium alloy-SiC fiber composites. Distinctly different behaviors were observed in the two systems. The differences were attributed to the formation of a substantial interfacial reaction layer in one of the composites which changed the interfacial chemistry and the resulting debond topography. The reaction layer caused an increase in the interfacial bond strength and in the roughness of the debonded interface. The latter resulted in substantially increased sliding friction. Although both composite interfaces exhibited some roughness, only one showed a seating drop during fiber push-back. This is related to the fact that the reaction layer which formed in one of the composites was severely degraded during fiber pushout. Although this interface was still rough, the roughness correspondence between fiber and matrix was destroyed during sliding, such that seating was no longer possible.
Consolidation of Continuous Fiber, Intermetallic-Matrix Composites
Authors: Semiatin S. L. , Goetz R. L. , Kerr W. R. 
Published: March 2011

ABSTRACTProcessing routes for fabrication of continuous fiber, intermetallic-matrix composites are reviewed. These methods include conventional and isostatic hot pressing of layups of matrix material (e.g. foil or powder cloth) and fiber mats; consolidation of monotapes made by techniques such as arc, plasma, vapor, or electron beam deposition or tape casting; and liquid metal infiltration-base methods. The advantages and disadvantages of the various methods are discussed. Particular attention is focussed on HIP consolidation via foil-fiber-foil techniques. Process modeling techniques to assess the effects of pressure, temperature, and time on consolidation behavior are described. By this means, maps to delineate the interaction of process variables in such methods can be developed and applied for process optimization.
Process Modeling for Titanium Aluminide Matrix Composites
Authors: Bampton C. C. , Graves J. A. , Newell K. J. , Lorenz R. H. 
Published: March 2011

ABSTRACTConsolidation of continuous fiber-reinforced titanium aluminide matrix composites (TMC) by the foil/fiber/foil method has traditionally taken an empirical approach utilizing processing cycles derived by simple trial and error. In an effort to reduce the empirical nature of producing TMC, a simple but effective analytical approach is employed. This approach analyzes the effect of fiber and foil geometries on consolidation parameters by combining a physical constitutive creep model with computational methods of interpreting raw materials characterization data. Examples of SCS-6/super a2(Ti-25Al-10Nb-3Mo-lV) and Saphikon/γ-TiAl composites consolidation are discussed by comparing the model predictions with equivalent validation specimen microstructures.
In-Situ Synthesis of Intermetallic Matrix Composites
Authors: Shah Dilip M. , Anton Donald L. 
Published: March 2011

ABSTRACTIn pursuing the development of intermetallics as high temperature structural materials, a composite approach is considered necessary for achieving room temperature toughness. If not further qualified, the term “composite” generally implies the application of mechanical processes by which a strong reinforcing phase is dispersed in the matrix, often as aligned continuous fibers. While this approach appears simple and promising in principle, in practice it is limited by the availability of compatible fibers, controlled processing, and microstructural homogeneity and reproducibility. Alternatively, the composite microstructures may be created in-situ either synthetically or naturally. In synthetically derived composites, the desired phases may be deposited layer by layer using such techniques as chemical vapor deposition (CVD), and potentially a variety of lithographic techniques may be employed to control the microstructure. However, such techniques are currently rate limited and not well developed for the large dimensions required for structural composites. In contrast, the in-situ composites, which rely on phase separation by either eutectic solidification or solid state precipitation, are economical and especially well suited for generating naturally compatible ductile phase toughened composites with uniform fine scale microstructures. This paper attempts to classify these approaches in perspective, discuss the benefit of in-situ composites relying on the natural phase separation mechanisms, and review the current activities with emphasis on the concept of ductile phase toughening.
Evaluation of Various Intermetallic Matrix - Ceramic Particle Systems for Melt Processing of Metal Matrix Composites
Authors: Sen S. , Dhindaw B. K. , Stefanescu D. M. 
Published: March 2011

ABSTRACTThe possibility of incorporating SiC or TiC particulate reinforcements in a Ni3Al matrix through the melt processing route was examined. Interface bonding and thermal stability of SiC and surface treated SiC in Ni3Al has been investigated through sessile drop and DTA experiments. Feasibility of various processing techniques such as the mechanical mixing method and the vacuum infiltration method was also explored.
Microstructural Characterization of Al2O3/Gamma Titanium Aluminide Composites
Authors: Das G. , Krishnamurthy S. 
Published: March 2011

ABSTRACTAlumina (A12O3) fibers were incorporated into gamma titanium aluminide(TiAl) based powders by hot isostatic pressing (HIP'ing). The microstructure of as-HIP'd and heat treated composite specimens were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM studies reveal the presence of an amorphous reaction zone at the fiber/matrix interface. Numerous dislocations, dipoles and loops as well as twins are observed in A12O3fibers. In addition, it is determined that the fiber/matrix interface stability is significantly affected by the matrix microstructure.
Epitaxial Buffer Layers on (012) Sapphire and (100) SrTiO3 for the Integration of YBa2Cu3Ox in Microwave Devices and Squids
Authors: Schmidt H. , Vollnhals G. , Gieres G. , Wersing W. , Kinder H. 
Published: March 2011

ABSTRACTThe epitaxial growth of YBa2Cu3Ox films on sapphire for microwave applications requires epitaxial buffer layers hindering interdiffusion. Therefore the epitaxial growth of YSZ, the layer sequence Y2O3/YSZ, and Y2O3 on (012) sapphire was examined. In addition the growth of MgO and srTiO3 on sapphire substrates and the growth of MgO and CeO2 on SrTiO3 substrates was studied by X-ray diffraction, X-ray pole figure measurement and RBS-ion channeling. With a combination of these buffer layers bi-epitaxial grain boundaries in YBa2Cu3Ox films can be fabricated in future.
Space Group and Fundamental Vibrations of the (RElBa2Cu3O7)m (RE2Ba2Cu3O7)n Superlattices
Authors: Mirovitskii V. Yu. 
Published: March 2011

ABSTRACTThe (RE1Ba2Cu3O7)m (RE2Ba2Cu3O7)n superlattices (SL) with the superporiod d along [100]. [010] and [001] have been considered as a single crystals with primitive cells formally multiplied duo to ordering of rare earth atoms in an initial hypothetical mixed system (RE1pRE21-p)Ba2Cu3O7 By means of symmetry methods it is found that the suporporiodicity in those SL, unlike Ge/Si or GaAs/AlAs. keeps the initial space group Pmmm at any m and n. On the contrary, the obtained Table of the SL atoms distribution over Wyckoff positions indicates that the type, multiplicity and the number of the positions essentially depend on d and Cm.nD. Those data are used for group thoorotical classification of the fundamental vibrations of SL's. The analysis of spectrum changes under transformation from the initial compound to SL is performed. In particular, it is found out that already at the lowest m and n the oven vibrations of RE, Cul and Ol, occupying only one-fold positions in the initial structure, occur. Also for each d the typo of spectrum is shown to depend on both m+n and the fact if the pair (m.n) is even-oven, odd-odd or oven-odd.
New Perovskite Based Structures in the Bi-Sr-O System
Authors: Bokhimi  , Portilla M. 
Published: March 2011

ABSTRACTWe report one amorphous and four new crystalline phases in the Bi-Sr-0 system. The structure of three of the crystalline phases was identified. The Br10Bi6O24-y phase, which is cubic with space group Fm3m and cell parameter a = 0.8471(1) nm. The SreBi10O27-y phase, which is tetragonal with the space group I/mmm, and cell parameters a = 0.6007(1), c = 0.8376(1) nm. The SreBi10O27-y phase, which is tetragonal with space group I/mmm and cell parameters a = 1.3221(1), c = 0.4249(1) nm. We show that in the crystalline structures Sr and Bi occupy equivalent sites.
Properties of Hot Isostatically Pressed Bi2Sr1.7CaCu2Ox
Authors: Nash A. S. , Goretta K. C. , Miller D. J. , Biondo A. C. , Shi Donglu , Sengupta S. , Poeppel R. B. 
Published: March 2011

ABSTRACTDense Bi2Sr1.7CaCu2Ox (2212) superconductor pellets were made by hot isostatic pressing in an inert atmosphere. The pellets exhibited a small amount of preferred orientation of the grains. The transport critical current density (Jc) values were very low for all specimens. Dislocations, planar faults, and intergrowths of the Bi2Sr2CuOx phase, which were produced during the pressing, caused the intragranular Jc to increase substantially.
Anomalous Low-Field Magnetic Behaviour of High-TC Superconductors
Authors: Tai M. F. , Wang H. J. , Lin C. C. , Wang H. L. 
Published: March 2011

ABSTRACTWe report on the studies of low-field magnetic properties in the well-characteristic superconducting LaCaBaCu3Oy, YBa2Cu3Oy, YaBa4Cu8Oy, (La1–85Sr0–15)CuO4-y, (Tl0–5Pb0–5)Ca2Sr2Cu3Oy and (Bi2−xPbx)Ca2Sr2Cu3Oy oxides. The studies of magnetic properties include ac zero-field cooled (ZFC), field-cooled (FC), and ac susceptibilities, and their dependences on the applied magnetic field and temperature. As the applied dc magnetic field is low enough, the FC susceptibility varies flat with the increasing of temperature from low temperature, but the diamagnetic signal becomes increasing at some temperature and reaches to the maximum values, and then continously decreases with temperature, at last the diamagnetism rapidly transfers to paramagnetism with temperature going to above Tc. The magnetization reduction at low temperature significantly appears at the low dc magnetic field and exists within a lot of single-phase high-Tc superconductors. However, this phenomenon is not observed in the measurements of low-frequency ac complex susceptibility for the ac applied fields from 0.001 G to 10 G and disappears for higher dc applied field. But, there exists a two-step drop in ac and ZFC susceptibilities curve and the drop correlates with the de FC magnetization dip. The magnetic field range of the dip occurrence is dependent on specimens. The strange magnetic property may be regard with superconducting coupling link in grain boundaries and interpreted by the grain-cluster model associated with Josephson effect.
Thickness Dependence of Vortex Pinning in Epitaxial Tl-Ca-Ba-Cu-O Thin Films
Authors: Venturing E. L. , Lee W. Y. , Morosin B. , Ginley D. S. 
Published: March 2011

ABSTRACTThe critical current density inferred from magnetization hysteresis for epitaxial Tl2Ca2Ba2Cu3O10 films on LaAlO3 exhibits a pronounced increase with film thickness in the high-field, high-current regime. This thickness dependence does not extend to comparatively “thick” single crystals, however, suggesting that the grain boundaries play a major role in collective vortex pinning for Tl-based superconducting thin films.
Sensitive Method of Measuring Microwave Surface Impedance of Superconducting Films
Authors: Jiang H. , How H. , Widom A. , Vittoria C. 
Published: March 2011

ABSTRACTWe used a microwave technique in which a small strip of YBCO film is induced to self-resonant in order to measure the surface impedance at 21 GHz. Both the amplitude and phase of the transmission coefficient, S21, as a function of frequency was measured at different temperatures. The surface resistance, Rs, was obtained from at resonant frequency, where Z0is the waveguide impedance. The surface reactance, Xa was obtained from the measurement of frequency shift with temperature. We found that Ra changed about 3 orders of magnitude as T decreased from 90K to 80K reaching a low value of 4.9 × 10−4μ. From Ra and Xa we deduced the London penetration depth to be λ ∼ 1800Å at 4K and 8000Å at 86.5K.
Hole Concentration and Tc in the TI2-x-zBa2+xCa2+xCu3O10-y System
Authors: Paranthaman M. , Foldeaki M. , NaziriPour A. , Hermann A. M. 
Published: March 2011

ABSTRACTSingle phase Tl-2223 samples were prepared in the TI2-x-zBa2Ca2+xCu3O10-y (z represent Tl vacancies in the range 0.22 – 0.27 and y represent oxygen vacancies in the range 0.17 – 0.33) system with x between 0 and 0.4. A small impurity phase was found at x = 0.6. All samples were found to be tetragonal. The Tc varied between 112 and 118 K for the “as-synthesized” samples. After post-annealing in a sealed quartz tube under vacuum at 750*deg;C for 10 days, the Tc increased from 116 to 122 K for x = 0.3 and from 118 to 120 K for x = 0,4 samples. Although x = 0.3 sample had small impurity phases after post-annealing, a large amount of impurity phases were found for x = 0.4 sample after post-annealing. Wet chemical analysis showed that all samples were both Tl and oxygen deficient. The Tc was found to increase with increasing hole concentration. The origin of the holes for all these samples is due to Ca2+ substitution on the TI3+ sites and overlap of Tl-6s band with the conduction band of the CuO2 sheets.
In-Situ Growth of C-Axis Oriented YBa2Cu3O7−x on Silicon with Composite Buffer Layers by Plasma Enhanced Metalorganic Chemical Vapor Deposition
Authors: Zhang Jiming , Gardiner Robin , Kirlin Peter S. 
Published: March 2011

ABSTRACTYBa2Cu3O7−x thin films have been grown in-situ on Si (100) with a composite buffer layer of Pt/Ta/ONO (ONO stands for a S1O2 / Si3N4 /SiO2 trilayer) by plasma enhanced metal organic chemical vapor deposition (PE-MOCVD). X-ray diffraction measurements indicate that c-axis oriented YBa2Cu3O7−x films are formed in-situ at substrate temperatures as low as 650 °C on Pt/Ta/ONO/Si. The composite P/Ta/ONO provided an adherent metallic interlayer and effectively prevented the interaction between YBa2Cu3O7−x and Si. Four probe resistivity measurements indicate the onset of superconductivity at 92 K and achieved zero resistance at 65 K.
Heteroepitaxial Bi2Sr2CaCu2Ox Superconducting thin films Deposited on LaA1O3 by Solid Phase Epitaxy and OMCVD
Authors: Chen J. , Lu H. A. , DiMeo F. , Wessels B. W. , Schulz D. L. , Marks T. J. , Schindler J. L. , Kannewurf C. R. 
Published: March 2011

ABSTRACT-Heteroepitaxial superconducting Bi,Sr2CaCu2Ox (BSCCO 2212) thin films have been formed by solid phase epitaxy from amorphous films deposited on (100) LaA1O3 single crystal substrates by organometallic chemical vapor deposition. The epitaxial structure of the film is confirmed by x-ray diffraction including θ/2θ and Φ (in plane rotation) scans. Cross-sectional high resolution transmission electron microscopy indicates that the film-substrate interface is nearly atomically abrupt. Improvements in superconducting properties of the epitaxial thin films are noted in comparison to highly textured films deposited on MgO.
Destruction of Scalino Law for Flux Pinning in Layered Structures
Authors: Lykov A. N. , Zdravkov V. I. 
Published: March 2011

ABSTRACTThe multilayers based on Nb/NbO (S-I-S) were investigated in external magnetic fields at various temperatures. It was found that the shear deformation of the solid vortex lattice de-termenes critical current density in the case of large period structures and high parallel fields. The solid vortex lattice can be destroyed by decreasing of both the period and the upper critical field. The qualitative change of the magnetic field dependence of the volume pinning force was observed as temperature was increasing. It reveals structural transitioon from elasti-cally deformed flux line lattice to plastically deformed one. Thus the scaling low is destructed for these structures. We have determened the volume pinning force by direct summing of elementary pinning forces in oxide layers in this case.
Power-Law Scaling Behaviors and Kosterlitz-Thouless Transition in the Resistive State of Ultra-Thin High-Tc Superconducting Films
Authors: Onogi T. , Sugano R. , Murayama Y. 
Published: March 2011

ABSTRACTBy means of a Langevin dynamic simulation we studied the current-voltage characteristics of a two-dimensional (2D) Josephson-coupled lattice as a model high-Tc superconducting film. The result illustrates qualitative features of non-Ohmic power-law scaling behaviors observed in transport measurements, including striking effects of applied magnetic fields. We thereby suggest that the Kosterlitz-Thouless transition associated with 2D vortex-antivortex pairs may dominate over the resistive transition in weak magnetic fields H/Hc2 ≪C 1. Through a simple theoretical estimate, we also show that the KT model illustrates the thickness-dependence of resistive transition temperature and electric field effect in ultra-thin YBa2Cu3O7−x films.
Relation of Constituents with Superconducting Characteristics in Low-Temperature-Preheated YBCO Ceramics
Authors: Nishino Junya , Nishikawa Hiroaki , Ayabe Muneo , Ikegami Yuji 
Published: March 2011

ABSTRACTYBCO bulk ceramics pre-heated at low temperature before sintering were studied on the structure and superconducting properties mainly by varying the concentration of Ba/Y ratio.At 15.8–16.2wt% of the oxygen content Oc calcurated from the compositions of yttrium, barium and copper on the assumption that the valence of copper is 2, (123) phase is main and critical temperature(Tc) and critical current density(Jc) reach to 88–90K and about 103A/cm2, respectively.It is presumed that there is a possibility of the exixtence of oxygen deficient and disordered phase in addition to (123) and (211) phases and BaCuO2.
Superconducting Properties of Ultrathin YBa2CU3O7 Films
Authors: Terashima T. , Shimura K. , Daitoh Y. , Yano Y. , Bando Y. , Matsuda Y. , Komiyama S. 
Published: March 2011

ABSTRACTUltrathin YBa2CU3O7 (YBCO) films were epitaxially grown on non-superconducting PrBa2CU3O7 (PrBCO) buffer layer by reactive evaporation, in which the crystal growth was controlled through the monitoring of reflection high energy electron diffraction (RHEED) specular intensity oscillations. Atomic force microscope (AFM) observation reveals that the steps in the surface of ultrathin YBCO films (∼100Aå) have one-unit-cell height, implying a unit cell-by-unit cell growth manner. One-unit-cell thick (1-UCT) YBCO layer exhibits superconductivity when charge reservoir layers of BaO-CuO-BaO are located above and below the CuO2 bilayer interposed with an Y layer. Essential transport properties of the normal state in bulk YBCO, such as T-linear dependence of resistivity and T-1 dependence Of Hall resistivity, are found to be inherent in the individual CuO2 bilayer. Study of diagonal and Hall resistivities provides evidence of Kosterlitz-Thouless transition to be occurred in 1-UCT YBCO.