bluuebunny/crossref_metadata_2025 huggingface dataset:
Irreversible transformation in as-cast FeAl B2-ordered alloy obtained by melt spinning
Authors: Bonetti E. , Montanari R. , Testani C. , Valdrè G.
Published: March 2008

The aim of the work described in the present paper was to investigate the microstructural stability during annealing treatments of a Fe–Al alloy obtained by melt spinning. To this purpose internal friction (IF) and dynamic modulus (Md) measurements were employed, and the results correlated with x-ray diffraction, optical microscopy, and scanning and transmission electron microscopy observations. In particular, the B2-ordered Fe–38A1–2Cr–0.015C–0.003B (in at.%) alloy was studied during repeated heating runs from room temperature to 823 K by IF and Md. The modulus exhibited a broad maximum (in the range of 600–800 K) only in the first run. On the basis of transmission electron microscopy and x-ray diffraction analysis, the irreversible transformation was explained by considering a two-stage process that occurs when vacancies in supersaturation move toward dislocations. The first stage is connected to dislocation locking; the second one is due to annihilation of some vacancies by dislocation climb.
Morphology and gas barrier properties of thin SiOxcoatings on polycarbonate: Correlations with plasma-enhanced chemical vapor deposition conditions
Authors: Erlat Ahmet G. , Wang Bo-Chy , Spontak Richard J. , Tropsha Yelena , Mar Kevin D. , Montgomery David B. , Vogler Erwin A.
Published: March 2008

Plasma-enhanced chemical vapor deposition of SiOx coatings on thermoplastics provides a viable route for production of transparent composite materials with high fracture toughness and high gas barrier properties, which are important considerations in the food packaging and biomedical device industries. By examining several series of systematically varied SiOx/polycarbonate composites, we have identified design correlations between coating characteristics (thickness, density, surface roughness, and O2 transmission) and deposition conditions (time, power, pressure, and flow rates). Of particular interest is the observation that the thermal activation energy for O2 permeation through these composites increases (by up to 17 kJ/mol) as their barrier efficacy increases.
Model analysis of boundary residual stress and its effect on toughness in thin boundary layered yttria-stabilized tetragonal zirconia polycrystalline ceramics
Authors: Shi J. L. , Lu Z. L. , Guo J. K.
Published: March 2008

The average thermal residual stress in a continuous boundary phase in polycrystalline ceramic composites was calculated with a simple thin boundary layer model, and a criterion for the self-cracking of the boundary phase was derived under a certain assumption. From the proposed model, the toughness of the materials can be increased by both tensile and compressive stress at boundaries when the crack propagates transgranularly. The toughness will be increased when the stress at boundary is compressive for intergranular fracture mode. The maximum increase is predicted to be achieved at boundary phase contents below 33%. The experimental results for yttria-stabilized tetragonal zirconia polycrystalline ceramics doped with different kinds of grain-boundary phase is in a qualitative agreement with the prediction by the model, but the toughness increase is largely dependent on the distribution feature of glass phases.
An experimental and modeling investigation of particle production by spray pyrolysis using a laminar flow aerosol reactor
Authors: Lenggoro I. Wuled , Hata Takeshi , Iskandar Ferry , Lunden Melissa M. , Okuyama Kikuo
Published: March 2008

The influence of operating parameters on the morphology of particles prepared by spray pyrolysis was investigated using a temperature-graded laminar flow aerosol reactor. Experimentally, zirconia particles were prepared by spray pyrolysis using an aqueous solution of zirconyl hydroxide chloride. Hollow particles were formed if the reactor temperature was high, the temperature gradient was too large, the flow rate of carrier gas was high, and the initial solute concentration was low. A numerical simulation of the pyrolysis process was developed using a combination of two previous models. The simulation results compared well with the experimental results.
Giant magnetoimpedance in CoP electrodeposited microtubes
Authors: Sinnecker J. P. , García J. M. , Asenjo A. , Vázquez M. , García-Arribas A.
Published: March 2008

Co90P10 amorphous microtubes with thickness ranging from 2 to 19 μm were electrodeposited onto Cu wire substrates. Samples exhibit radial magnetic anisotropy as deduced from hysteresis loops and magnetic force microscopy imaging. These microtubes show quite noticeable giant magnetoimpedance effect (GMI) with amplitude depending on layer thickness and frequency. The hysteresis in the GMI curves is small, which can be ascribed to the radial anisotropy. Such small hysteresis is of importance for technological applications.
Titanium environment in TiO2–BaO–ZnO–B2O3 glasses by x-ray absorption spectroscopy
Authors: Watanabe N. , Ramos A. Y. , Alves M. C. M. , Tolentino H. , Alves O. L. , Barbosa L. C.
Published: March 2008

The local environment of titanium in glasses of the system TiO2–BaO–ZnO–B2O3 was studied by x-ray absorption spectroscopy. In all glasses, for TiO2 content varying from 35 to 49 mol%, the titanium atoms are mainly fourfold coordinated network formers. For the glass with the highest titanium content, about 20% of the titanium enters into a sixfold environment, indicating the presence of precrystalline nuclei. These nuclei are responsible for the decrease of the optical performance of the glass above threshold titanium content, prior to any observable crystallization.
Copper-associated aluminum ionized center [AlO4−/Cu++]+ in a γ-irradiated copper (I)-containing silica glass
Authors: Debnath Radhaballabh
Published: March 2008

A new type of aluminum ionized center associated with the copper ion [AlO4−/Cu++]+ has been observed in a copper(I)-containing silica glass upon γ-irradiation at room temperature. The center, unlike many other previously reported monovalent cation-compensated aluminum ionized hole centers [AlO4/M+]+, where M+ = H+, Li+, Na+, Ag+, etc., behaves more like a simple ionized center rather than an ionized hole center. We argue that complete compensation of the hole on the aluminum ion of the center becomes possible because of the compensating copper ion. This is accomplished by the donation of an electron by the cuprous ion to the neighboring irradiationgenerated [AlO4]0 hole via that oxygen atom of the (AlO4), which is nearest to the cation.
Cyclic Nanoindentation and Raman Microspectroscopy Study of Phase Transformations in Semiconductors
Authors: Gogotsi Yury G. , Domnich Vladislav , Dub Sergey N. , Kailer Andreas , Nickel Klaus G.
Published: March 2008

This paper supplies new interpretation of nanoindentation data for silicon, germanium, and gallium arsenide based on Raman microanalysis of indentations. For the first time, Raman microspectroscopy analysis of semiconductors within nanoindentations is reported. The given analysis of the load-displacement curves shows that depth-sensing indentation can be used as a tool for identification of pressure-induced phase transformations. Volume change upon reverse phase transformation of metallic phases results either in a pop-out (or a kink-back) or in a slope change (elbow) of the unloading part of the load-displacement curve. Broad and asymmetric hysteresis loops of changing width, as well as changing slope of the elastic part of the loading curve in cyclic indentation can be used for confirmation of a phase transformation during indentation. Metallization pressure can be determined as average contact pressure (Meyer's hardness) for the yield point on the loading part of the load-displacement curve. The pressure of the reverse transformation of the metallic phase can be measured from pop-out or elbow on the unloading part of the diagram. For materials with phase transformations less pronounced than in Si, replotting of the loaddisplacement curves as average contact pressure versus relative indentation depth is required to determine the transformation pressures and/or improve the accuracy of data interpretation.
Photoluminescence Spectra of Zn1-xCdxAl2Se4 Single Crystals
Authors: Hyun Seung-Cheol , Kim Chang-Dae , Park Tae-Young , Kim Hyung-Gon , Jin Moon-Seog , Lee Choong-Il , Goh Jae-Mo , Kim Wha-Tek
Published: March 2008

We investigated the photoluminescence spectra as well as the crystal structure and optical energy gaps of the Zn1-xCdxAl2Se4 single crystals grown by the chemical transport reaction method. It was shown from the analysis of the observed x-ray diffraction patterns that these crystals have a defect chalcopyrite structure for a whole composition. The lattice constant a increases from 5.5561 A for x = 0.0 (ZnAl2Se4) to 5.6361 A for x = 1.0 (CdAl2Se4) with increasing x, whereas the lattice constant c decreases from 10.8890 A for x = 0.0 to 10.7194 A for x = 1.0. The optical energy gaps at 13 K were found to range from 3.082 eV (x = 1.0) to 3.525 eV (x = 0.0). The temperature dependence of the optical energy gaps was well fitted with the Varshni equation. We observed two emission bands consisting of a strong blue emission band and a weak broad emission band due to donor–acceptor pair recombination in the Zn1-xCdxAl2Se4 for 0.0 ⩽ x ⩽ 1.0. These emission bands showed a red shift with increasing x. The energy band scheme for the radiative mechanism of the Zn1-xCdxAl2Se4 was proposed on the basis of the photoluminescence thermal quenching analysis along with the measurements of photo-induced current transient spectroscopy. The proposed energy band model permits us to assign the observed emission bands.
Heat Resistance of Sn–9Zn Solder/Cu Interface with or without Coating
Authors: Suganuma Katsuaki , Murata Toshikazu , Noguchi Hiroji , Toyoda Yoshitaka
Published: March 2008

The potential of the newly developed Sn–9Zn solder paste as a lead-free solder, especially focusing on the stability at high temperature, was examined. The initial interface strength between Sn–9Zn and Cu, about 50 MPa by the tensile test, is higher than other interfaces such as Sn–37Pb/Cu. While the Sn–9Zn/Cu interface maintains the high strength level after heat exposure at 125 °C, the heat exposure at 150 °C degrades strength seriously. The degradation at 150 °C is caused by dissipation and by disruption of the Cu–Zn reaction layer at the interface. Where the Cu–Zn layer is eroded to form a whole, Sn directly reacts with a Cu substrate to form a thick Sn–Cu reaction region. Such an interfacial morphology change causes the serious degradation. With the Ni/Pd/Au coating on a Cu substrate, the interface becomes much stronger than the direct interface. Even after heat exposure at 150 °C, strength degradation is not so significant. Zn segregates into the coating layer. During high-temperature exposure, Ni and Pd diffuse each other. Zn also diffuses into the coating layer to form compounds, and as a result, a depleted zone of Zn is formed in the solder close to the interface.
Stereophotogrammetric Investigation of Overload and Cyclic Fatigue Fracture Surface Morphologies in a Zr–Ti–Ni–Cu–Be Bulk Metallic Glass
Authors: Tatschl A. , Gilbert C. J. , Schroeder V. , Pippan R. , Ritchie R. O.
Published: March 2008

Fracture surfaces of a recently developed Zr41.2Ti13.8Cu12.5Ni10.0Be22.5(at.%) bulk metallic glass were investigated using a three-dimensional surface reconstruction technique. Stereoscopic scanning electron microscopy of both fatigue and overload fracture surfaces permitted the creation of digital elevation models that were used to quantify important fracture surface features. Characterization of the surfaces revealed striations of nearly constant spacing on fatigue surfaces and a vein morphology characteristic in amorphous metals on the overload fracture surfaces. Additionally, at the onset of critical failure, crack-tip openings of ˜16 μm were observed that were consistent with measured values of fracture toughness. Interestingly, at the onset of fracture, deformation was confined to one side of the fracture plane, possibly because of the asymmetric emission of shear bands from the crack tip, consistent with the highly inhomogeneous nature of deformation in this alloy.
Preferred Orientation of Copper Phthalocyanine Thin Films Evaporated on Amorphous Substrates
Authors: Resel R. , Ottmar M. , Hanack M. , Keckes J. , Leising G.
Published: March 2008

A series of copper phthalocyanine thin films were prepared on amorphous substrates using physical vapor deposition at ambient temperature. Different sample preparation conditions were used: the deposition rate was varied, and the substrates was static or rotating. The preferred orientation in the thin film was studied as a function of the deposition conditions. X-ray diffraction analysis was performed using θ/2θ and pole figure measurements. In the case of layers prepared at low deposition rates and using nonrotating substrates, a very strong fiber texture was detected with (100) crystallographic planes oriented preferably parallel to the substrate surface. At higher deposition rates, an additional second type of preferred orientation was observed with (110) planes oriented preferably parallel to the substrate surface. In the case of layers prepared with rotational substrates, the (110) type of preferred orientation was quantitatively more strongly developed. If we consider electronic band structure calculations, these results imply that the electron/hole transport through the thin films is enhanced for films prepared at high deposition rates and rotating substrates.
Temperature Dependence ofin situConstituent Properties of Polymer-infiltration-pyrolysis-processed Nicalon™ SiC Fiber-reinforced SiC Matrix Composite
Authors: Guo Shuqi , Kagawa Yutaka
Published: March 2008

Temperature dependence ofin situfiber strength, effective interface shear stress, Young's modulus of matrix, and matrix fracture energy in a polymer-infiltrationpyrolysis (PIP)-processed two-dimensional plain-woven fabric carbon-coated Nicalon™ SiC fiber-reinforced SiC matrix composite was studied through a tensile test in air at 298 (room temperature), 800, and 1200 K.In situfiber strength and effective interface shear stress were determined by fracture mirror size and fiber pullout length measurements, respectively. The fiber strength was insensitive to test temperature up to 800 K but dropped significantly at 1200 K. Conversely, the interface shear stress showed a strong temperature dependence, decreasing at 800 K and drastically increasing at 1200 K. The temperature dependence of both values was reasonably explained. Temperature dependence of Young's modulus of matrix was derived from Young's modulus of the composite and fiber and ranged from ≈40 to ≈38 GPa. Matrix fracture energy was also determined from the transverse matrix cracking stress and ranged from ≈16 to ≈5.5 J/m2. Both Young's modulus of matrix and the matrix fracture energy showed only slight temperature dependence up to 800 K; however, both values decreased significantly at 1200 K.
Sintering of Nanopowders of Amorphous Silicon Nitride Under Ultrahigh Pressure
Authors: Li Ya-Li , Liang Yong , Zheng Fen , Ma Xian-Feng , Cui Suo-Jing
Published: March 2008

Nanopowders of amorphous silicon nitride were densified and sintered without additives under ultrahigh pressure (1.0–5.0 GPa) between room temperature and 1600 °C. The powders had a mean diameter of 18 nm and contained ∼5.0 wt% oxygen that came from air-exposure oxidation. Sintering results at different temperatures were characterized in terms of sintering density, hardness, phase structure, and grain size. It was observed that the nanopowders can be pressed to a high density (87%) even at room temperature under the high pressure. Bulk Si3N4 amorphous and crystalline ceramics (relative density: 95–98%) were obtained at temperatures slightly below the onset of crystallization (1000–1100 °C) and above 1420 °C, respectively. Rapid grain growth occurred during the crystallization leading to a grain size (>160 nm) almost 1 order of magnitude greater than the starting particulate diameters. With the rise of sintering temperature, a final density was reached between 1350 and 1420 °C, which seemed to be independent of the pressure applied (1.0–5.0 GPa). The densification temperature observed under the high pressure is lower by 580 °C than that by hot isostatic pressing sintering, suggesting a significantly enhanced low-temperature sintering of the nanopowders under a high external pressure.
Reversing effect of electropulsing on damage of 1045 steel
Authors: Zhou Yizhou , Qin Rongshan , Xiao Suhong , He Guanhu , Zhou Benlian
Published: March 2008

The influence of electropulsing on the damage of 1045 steel was studied. The results show that electropulsing can substantially increase the strength and ductility of the damaged material, with a little decrease of the Martensite hardness. After the treatment of electropulsing, the microstructure around the crack is modified, and the new structure can prevent the crack from growing. The healing effect of electropulsing on crack is discussed. It is thought that the temperature and thermal compressive stress caused by electropulsing are the main factors causing the healing effect.
Analysis of the fluoride effect on the phase-selective growth of TlBa2Ca2Cu3O9−x thin films: Phase evolution and microstructure development
Authors: McNeely Richard J. , Belot John A. , Marks Tobin J. , Wang Yanguo , Dravid Vinayak P. , Chudzik Michael P. , Kannewurf Carl R.
Published: March 2008

Phase-selective growth of TlBa2Ca2Cu3O9−x films is greatly enhanced by annealing chemical vapor deposition derived BaCaCuO(F) precursor films in the presence of TlF. Nucleation of superconducting phases (≥840 °C under O2) progresses in the order 2212 → 2223 → 1212 → 1223. Annealing at 855 °C results in well-defined platelet grains, a significant number of which are a-axis oriented. Residual fluoride is not detectable at any stage of the annealing process. Thin films synthesized by TlF annealing differ markedly from films processed in the presence of Tl2O3 with Tc = 103 K and Jc > 105 A/cm2 (5 K, 4.5 T).
Synthesis of Cr–Si intermetallic compounds by field-activated combustion synthesis
Authors: Maglia F. , Anselmi-Tamburini U. , Bertolino N. , Milanese C. , Munir Z. A.
Published: March 2008

The use of an electric field to activate the combustion synthesis of chromium silicides was investigated. Despite their relatively low adiabatic temperatures, all four silicides were synthesized by field-activated combustion synthesis. However, although self-propagating synthesis reactions were initiated, the products were not pure but contained other silicides and reactant phases. The purity of the samples increased with increasing field strength, and under the highest field, the products contained the desired silicide as the major phase with minor amounts of other stoichiometries. Observation of microstructural evolution in quenched reactions revealed the key role played by the liquid phases in the propagation of the combustion front. The phase Cr5Si3 was the first product of the interaction between the reactants when either solid–solid or solid–liquid processes were involved. These results were confirmed by isothermal solid–solid and solid–liquid diffusion couple experiments.
Fracture and R-curves in high volume fraction Al2O3/Al composites
Authors: Nagendra N. , Jayaram V.
Published: March 2008

Fracture toughness and fracture mechanisms in Al2O3/Al composites are described. The unique flexibility offered by pressureless infiltration of molten Al alloys into porous alumina preforms was utilized to investigate the effect of microstructural scale and matrix properties on the fracture toughness and the shape of the crack resistance curves (R-curves). The results indicate that the observed increment in toughness is due to crack bridging by intact matrix ligaments behind the crack tip. The deformation behavior of the matrix, which is shown to be dependent on the microstructural constraints, is the key parameter that influences both the steady-state toughness and the shape of the R-curves. Previously proposed models based on crack bridging by intact ductile particles in a ceramic matrix have been modified by the inclusion of an experimentally determined plastic constraint factor (P) that determines the deformation of the ductile phase and are shown to be adequate in predicting the toughness increment in the composites. Micromechanical models to predict the crack tip profile and the bridge lengths (L) correlate well with the observed behavior and indicate that the composites can be classified as (i) short-range toughened and (ii) long-range toughened on the basis of their microstructural characteristics.
Single-step fabrication of potassium tantalate films by hydrothermal-electrochemical method at lower temperatures
Authors: Wu Zhibin , Tsukada Tetsuji , Yoshimura Masahiro
Published: March 2008

Potassium tantalate thin films (KT) were hydrothermal-electrochemically and electrochemically synthesized on tantalum substrates under galvanostatic conditions in KOH solutions at temperatures from 50 to 150 °C. The pyrochlore structures were characterized by x-ray diffraction and scanning electron microscopy for the films formed under a variety of conditions. It was found that the reaction temperature, potassium hydroxide concentration, and current density significantly affect the formation and the morphology of the KT films. When the reaction temperatures were higher than 80 °C and the KOH concentrations were greater than 2.0 M, very crystalline films with excellent film flatness and good adherence on the substrate were obtained. Based on the experimental results, it was confirmed that the formation and growth of KT films by the hydrothermal-electrochemical and electrochemical method follow a dissolution-crystallization mechanism.
Phase diagram studies in the quasi binary systems LaMnO3–SrMnO3 and LaMnO3–CaMnO3
Authors: Majewski Peter , Epple Lars , Rozumek Michael , Schluckwerder Heike , Aldinger Fritz
Published: March 2008

The quasi binary systems LaMnO3–SrMnO3 and LaMnO3–CaMnO3 were studied. Both systems show a miscibility gap at intermediate La:Sr and La:Ca ratios below about 1400 °C in air. This phenomenon causes the decomposition of single-phase (La,Sr)MnO3−x and (La,Ca)MnO3−x solid solution into La-rich SrMnO3−x + Sr-rich LaMnO3−x and La-rich CaMnO3−x + Ca-rich LaMnO3−x at lower temperatures, respectively. At 1400 °C in the system LaMnO3–SrMnO3, a structure transformation of (La,Sr)MnO3 from orthorhombic to rhombohedral with increasing Sr content was not observed, and the structure of La0.7Sr0.3MnO3 was determined to be orthorhombic with a = 0.54927 ± 0.0009 nm, b = 0.54582 ± 0.0009 nm, and c 4 0.76772 ± 0.0034 nm.
Lifetime prediction of laser-precracked fused silica subjected to subsequent cyclic laser pulses
Authors: Dahmani Faiz , Schmid Ansgar W. , Lambropoulos John C. , Burns Stephen J. , Papernov Semyon
Published: March 2008

Measurements of fatigue failure strength of laser-cracked fused silica in air at room temperature for different numbers of laser shots and laser fluences are presented. The failure-strength variability is found to be due mainly to the spectrum of crack depths. Agreement with theory suggests the incorporation of a residual term into the failure–strength equation. Due to its sign, the residual stress is of mouth-opening displacement nature at the crack. Analysis of the residual stress data shows a linear proportionality with crack depth, whereas the failure–strength is inversely proportional to the square root of the crack depth.
Application of small-angle neutron scattering to the study of porosity in energetic materials
Authors: Mang Joseph T. , Skidmore Cary B. , Hjelm Rex P. , Howe Philip M.
Published: March 2008

Small-angle neutron scattering (SANS) and the method of contrast variation were used to measure porosity and crystallite surface area in the energetic system octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and to gauge the effects of mechanical deformation on the pore-size distribution and crystallite surface area. The crystallite surface area and the presence of voids (pores) in a high explosive system are known to affect its behavior and overall performance. Measures of these two quantities after an insult, resulting from various process and accident scenarios, can be used to predict the performance of an explosive system after process- and accident-related mechanical deformation. The contrast variation technique allows us to discriminate between internal pores and features that are on or contiguous with the crystallite surface. Measurements were conducted on loose powders of HMX (261 and 10 mm, volume averaged mean particle diameters) and pellets made by uniaxial consolidation to 7 and 10 vol% porosity, respectively. Analysis of the SANS data indicates significant alteration of the intragranular pore structure and systematic shifts in the surface area that are dependent upon mechanical deformation.
Thin Film Cracking and Ratcheting Caused by Temperature Cycling
Authors: Huang M. , Suo Z. , Ma Q. , Fujimoto H.
Published: March 2008

Layered materials are susceptible to failure upon temperature cycling. This paper describes an intriguing mechanism: cracking in a brittle layer caused by ratcheting in an adjacent ductile layer. For example, on a silicon die directly attached to an organic substrate, cracking often occurs in the silicon nitride film over aluminum pads. The silicon die and the organic substrate have different thermal expansion coefficients, inducing shear stresses at the die corners. Aided by cycling temperature, the shear stresses cause ratcheting in the aluminum pads. Incrementally, the stress relaxes in the aluminum pads and builds up in the overlaying silicon nitride film, leading to cracks.
Cross-poling Textures in a Lead Zirconate Titanate Piezoelectric Material
Authors: Wan Shan , Bowman Keith J.
Published: March 2008

Tetragonal ferroelectric materials are polarized to induce the anisotropy necessary for the piezoelectric effect. This poling of the material is inherently an orientation process. Pole figure texture measurements of poling and cross-poling in a lead zirconate titanate Navy VI material show domain motion. The resulting axisymmetric and three-dimensional textures demonstrate the contribution of 90° domain motion to piezoelectricity. Cross-poling results in strong orientations with lower applied fields than in the initial poling steps.
Synthetic Clay Excels in 90Sr Removal
Authors: Komarneni Sridhar , Kodama Tatsuya , Paulus William J. , Carlson C.
Published: March 2008

Tests with actual ground water from Hanford site, and fundamental studies of 2Na+ → Sr2+ exchange equilibria revealed that a synthetic clay is extremely selective for 90Sr with a high capacity for uptake. Comparative studies with existing Sr selective ion exchangers clearly revealed that the present synthetic clay exhibited the best performance for 90Sr removal from actual ground water collected from three different locations at Hanford. This novel Sr ion sieve is expected to be useful for the decontamination of the environment after accidental release and contamination with 90Sr.
Microstructure and Phase Stability Studies on Heusler Phase Ni2AlHf and G-phase Ni16Hf6Si7in Directionally Solidified NiAl–Cr(Mo) Eutectic Alloyed with Hf
Authors: Chen Y. X. , Cui C. Y. , Liu Z. Q. , He L. L. , Guo J. T. , Li D. X.
Published: March 2008

Small additions of Hf to directionally solidified NiAl–Cr(Mo) eutectic resulted in precipitation of a high density of Heusler phase Ni2AlHf along with fine G-phase Ni16Hf6Si7. The Heusler phase was mainly located on the grain boundary region. The fine G-phase formed in the presence of Si, which was a contamination resulting from contact with ceramic shell molds during directional solidification of the alloy. These fine G-phases were cuboidal in shape and coherent with the NiAl matrix. After hot isostatic pressing and aging treatment, the fine G-phases completely disappeared. The density of the Heusler phase was partially reduced, and the Heusler particles precipitated preferentially on the NiAl/Cr(Mo) interfaces and grain boundaries of the NiAl matrix. Some Heusler particles precipitated locally within the NiAl matrix, and small amounts of them precipitated within the Cr(Mo) phase. The structures of the NiAl/Ni2AlHf and NiAl/Ni16Hf6Si7interfaces were investigated by high-resolution electron microscopy. The habit plane of the fine G-phase was {001}NiAl. This result was in good agreement with calculation based on the linear elastic theory. The misfit dislocation network on the NiAl/Ni2AlHf (110) interface was calculated from the O-lattice model and compared with the observation, which showed good agreement.
Formation of Icosahedral Quasicrystalline Phase in Zr70TM10Pd20 (TM = Fe, Co, or Cu) Ternary Glassy Alloys
Authors: Matsushita M. , Saida J. , Li C. , Inoue A.
Published: March 2008

A nanoscale icosahedral quasicrystalline phase was confirmed as a primary precipitation phase in the melt-spun Zr70TM10Pd20 (TM = Fe, Co, or Cu) ternary glassy alloys with a two-stage crystallization process. The onset temperature of the transformation from amorphous to icosahedral phase is 713 K for Fe-, 696 K for Co-, and 680 K for Cu-containing alloys at the heating rate of 0.67 Ks−1. The size of the icosahedral particles is in the range of 20 to 50 nm for the Zr70Cu10Pd20 glassy alloy annealed for 120 s at 720 K. The icosahedral phase has a very fine particle size in a diameter range below 10 nm for the Zr70Fe10Pd20 and Zr70Co10Pd20 alloys. The crystallization reaction after the first exothermic peak results in the transition from the icosahedral to crystalline phases through a sharp exothermic reaction. Thus, the formation of the nanoscale icosahedral phase indicates the possibility that an icosahedral short-range order exists in the present glassy alloys.
Structural Characterization of Boron-doped Submicron Vapor-grown Carbon Fibers and Their Anode Performance
Authors: Nishimura K. , Kim Y. A. , Matushita T. , Hayashi T. , Endo M. , Dresselhaus M. S.
Published: March 2008

Structural evolution of undoped and boron-doped submicron vapor-grown carbon fibers (S-VGCFs) was monitored as a function of heat-treatment temperature (HTT). Based on x-ray and Raman data, over the range of HTT from 1800 to 2600 °C, it was found that boron atoms act as catalysts to promote graphitization due to boron's higher diffusivity. For the range of HTT from 2600 to 2800 °C, the process of boron out-diffusion from the host material induces defects, such as tilt boundaries; this process would be related with the improved capacity and Coulombic efficiency of boron-doped S-VGCFs. When 10 wt% S-VGCFs was used as an additive to synthetic graphite, the cyclic efficiency of the capacities was improved to almost 100%.
Dielectric Properties of Pb(Fe2/3W1/3)1−xMnxO3 Ceramics in the Temperature Range 200–600 K
Authors: Zhou Liqin , Vilarinho P. M. , Mantas P. Q. , Baptista J. L.
Published: March 2008

The dielectric properties of Mn-doped Pb(Fe2/3W1/3)1−xMnxO3 (x = 0, 0.001, 0.003, and 0.005) in the temperature range 200–600 K were investigated. Two sets of dielectric peaks, located at 200–350 K and 350–600 K, were observed. The intensity of the dielectric permittivity and loss factor peaks for both relaxations decreased with the increase in the Mn content and no peak occurred when x = 0.005. Nonlinear current–voltage (I–V) behavior was observed in the samples containing less than 0.005Mn. The activation energy values for the relaxations at 200–350 K and at 350–600 K were around 0.42 and 0.56 eV, respectively. The direct current conduction activation energies were around 0.41 eV. Nitrogen annealing eliminated the relaxation peaks at 200–350 K while oxygen annealing enhanced them. Both annealings eliminated the dielectric peaks at 350–600 K. The nonlinear I–V characteristic tended to vanish either after the oxygen or the nitrogen annealing treatments. Relaxation mechanisms are proposed and discussed. It is suggested that the relaxation at 200–350 K is related to electron hole while the relaxation at 350–600 K is attributed to microstructure-dependent space-charge polarization.
Phase and Microstructural Development of Sol-gel-derived Strontium Barium Niobate Thin Films
Authors: Oral A. Y. , Mecartney M. L.
Published: March 2008

Microstructural changes in sol-gel-derived SrxBa1−xNb2O6 (SBN) thin films were monitored as a function of Ba-to-Sr ratio (from x = 0 to x = 1), choice of substrate (Si or MgO), and processing variations. Sols were created using Ba, Sr, and Nb alkoxides dissolved in acetic acid. The relatively high decomposition temperature for the organics led to a tendency to form defects, but careful control of thermal process parameters could be used to produce a uniform film microstructure. An unexpected phase, interpreted as a hexagonal (pseudo-orthorhombic) variant of hexagonal BaNb2O6, was encountered in Ba-rich sol-gel-derived SBN powders and thin films annealed at 750 °C. Increased (001) orientation was observed for SBN thin films deposited on (100) MgO when fast thermal processing was used.
Micro-Raman Spectral Analysis of the Subsurface Damage Layer in Machined Silicon Wafers
Authors: Chen Long-Qing , Zhang Xin , Zhang Tong-Yi , Lin H. Y. , Lee Sanboh
Published: March 2008

In the present work we studied the depth of damage layer in machined silicon wafers that was incorporated with chemical etching using micro-Raman spectroscopy. Subsurface damage causes changes in the shape and intensity for the shoulder (450–570 cm−1) of the most intense band (519 cm−1) and the second band (300 cm−1) regions of the Raman spectrum. Etching reduces the thickness of the damage layer and, hence, the intensities at the shoulder and the second band. The intensities at the shoulder and the second band become stable when the damage layer is completely etched out. The shoulder consists of two Gaussian profiles: the major and the minor. The band for the major profile is independent of etching depth, but the band for the minor profile shifts toward the longer wave numbers with increasing etching period until the damage layer is completely etched out. The depth of the damage layer is determined by the profiles of the shoulder and the second band and confirmed by the band shift of the minor profile. Transmission electron microscopy (TEM) further verified the results with respect to the depth of the damage layer. TEM observation showed that dislocations and stacking faults are responsible for the subsurface damage.
Structural Characterization of Ceria–zirconia Powder Catalysts Prepared by High-energy Mechanical Milling: A Neutron Diffraction Study
Authors: Enzo S. , Delogu F. , Frattini R. , Primavera A. , Trovarelli A.
Published: March 2008

Neutron diffraction measurements were carried out on samples of CeO2–ZrO2powder catalysts prepared by high-energy mechanical milling. The formation of solid solution was evidenced across the entire composition range examined. Quantitative phase evaluation by the Rietveld method indicated formation of tetragonal structure for low CeO2content, whereas cubic solid solutions were the stable form at high CeO2loading. In addition, a pseudocubic or tetragonalt″cell with axial ratio of unity and with internal deformation of the oxygen sublattice was observed at intermediate composition (50 mol% CeO2). Thermal annealing up to 1000 °C showed expansion of the unit cell parameters; an increase in the degree of tetragonality at the expense of cubic and monoclinic phase was observed for composition CexZr1−xO2(x< 0.5).
Fatigue Properties of Lanthanum Strontium Manganate–lead Zirconate Titanate Epitaxial Thin Film Heterostructures Produced by a Chemical Solution Deposition Method
Authors: McNally Frank , Kim Jin Hyeok , Lange F. F.
Published: March 2008

A liquid-precursor process was used to produce an epitaxial all-oxide ferroelectric memory device structure. The lanthanum strontium manganate–lead zirconate titanate–lanthanum strontium manganate (LSMO–PZT–LSMO) structure used for this device shows excellent polarization and fatigue behavior with a remnant polarization Pr of 42 µC/cm2 and a coercive field Ec of 68 keV. The polarization was found to only slightly degrade after over 1010 fatigue cycles. This behavior is contrasted with epitaxial PZT using a metal top electrode. In addition, the use of a top LSMO electrode was a sufficient barrier to Pb loss during heating to allow subsequent (or prolonged) heat treatments that would generally lead to Pb loss.
Glass-forming Ability and Magnetic Properties of Nd70−xFe20Al10Cox Alloys
Authors: Fan G. J. , Löser W. , Roth S. , Eckert J. , Schultz L.
Published: March 2008

The influence of Co addition on the glass-forming ability of slowly cooled Nd70-xFe20Al10Cox alloys (0 ≤ x ≤ 10) was studied by x-ray diffraction, constant-rate heating calorimetry, and magnetic measurements. Without addition of Co, the as-cast Nd70Fe20Al10 cylinders of 3-mm diameter show a mixture of amorphous and crystalline phases after copper mold casting. Increasing the Co content promotes amorphization, and bulk amorphous specimens can be obtained for Nd60Fe20Al10Co10. No glass transition or supercooled liquid region before crystallization was observed for the bulk Nd60Fe20Al10Co10 alloy. The bulk amorphous alloy exhibits hard magnetic behavior with a remanence (Jr) of 0.09 T, a magnetization (J1500) of 0.13 T, and a coercivity (Hc) of 298 kAm−1. The Curie temperature for the as-cast Nd70-xFe20Al10Cox cylinders increases from 480 K for x =0 to 487 K for x = 10. The enhanced glass-forming ability for the Nd–Fe–Al-based alloys upon Co addition will be critically discussed with respect to classical nucleation theory and the formation of metastable ordered clusters upon solidification.
Single-crystalline Tungsten Nanoparticles Produced by Thermal Decomposition of Tungsten Hexacarbonyl
Authors: Magnusson Martin H. , Deppert Knut , Malm Jan-Olle
Published: March 2008

Nanometer-sized particles of W are of interest in semiconductor device research, where such particles may store electrons inside heteroepitaxially defined structures. In this paper, we present results concerning W particles produced by thermal decomposition of tungsten hexacarbonyl. By the described method, it was possible to produce size-selected, single-crystalline W particles in the size range between 15 and 60 nm. The sintering behavior of the particles was studied between ambient temperatures and 1900 °C. The particle morphology and structure were examined with high-resolution transmission electron microscopy and electron diffraction techniques. Particles sintered at the highest temperatures typically were single crystals, with well-developed facets. Some problems concerning a yield reducing charging mechanism are discussed.
An Innovative System for Fretting Wear Testing Under Oscillating Normal Force
Authors: Huq M. Z. , Butaye C. , Celis J-P.
Published: March 2008

Material damage caused by fretting wear is of significant concern in many engineering applications. This paper describes the design and performance of a new machine for the laboratory investigation of fretting wear under oscillating normal force (fretting mode II). The test machine uses an electromagnetic actuator to impose an oscillating normal force between the contacting bodies at a constant force amplitude over a wide range of frequencies. The principle of the actuation mechanism and the fretting wear induced with this particular wear test configuration are outlined in detail. Normal force and electrical contact resistance were measured on-line during fretting mode II wear tests. The performance of the wear test machine is illustrated by data obtained for different materials combinations, namely, hard materials, such as high-speed steel and (Ti,Al)N coatings oscillating against alumina ball counterbodies, and soft materials, such as a tin coating oscillating against the same. In general, wearing of the counterbodies was observed in the slip region. It has been observed that hard coatings and bulk ceramics are prone to fretting fatigue cracking. The evolution of electrical contact resistance in the case of the self-mated soft tin coatings tested under fretting mode II conditions is also reported.
Observation of Intergranular Films in BaB2O4-added BaTiO3 Ceramics
Authors: Lee Joon-Hyung , Kim Jeong-Joo , Wang Haifeng , Cho Sang-Hee
Published: March 2008

Distribution characteristics of boundary phase in BaB2O4 added BaTiO3 ceramics were investigated with a focus on the curvature difference of solid–liquid interfaces at two-grain and triple junctions. High-resolution transmission electron microscopy revealed that the triple junction of solid grains showed the positive curvature of solid–liquid interface and consisted of the mixture of liquid phase and crystallized BaB2O4 phase. On the other hand, flat amorphous thin film of 2.5-nm thickness was observed at the two-grain junction. This kind of boundary phase distribution characteristic was explained by the solubility difference between two kinds of junctions of solid grains that had different curvature of solid–liquid interfaces.
Annealing-induced Changes in the Electronic and Structural Properties of ZnTe Substrates
Authors: Garcia J. A. , Remón A. , Munñz V. , Triboulet R.
Published: March 2008

The aim of this study is to demonstrate that the electronic and structural properties of II–VI substrates, here ZnTe, can be dramatically affected by thermal heating at temperatures in the range of those typically used in the epitaxial metalorganic chemical vapor deposition processes. Photoluminescence response shows that annealing at these temperatures produces a reduction of the sample crystalline quality, decreasing the free exciton emission relative to the deep level related one. Some factors, like the change in the charge and stress state of dislocations, Cu diffusion, and oxygen incorporation, could be responsible for changes in the substrate properties, which can produce stresses and contamination in the deposited sample.
Characterization of the Interface Between the Bulk Glass Forming Alloy Zr41Ti14Cu12Ni10Be23 with Pure Metals and Ceramics
Authors: Schroers Jan , Samwer Konrad , Szuecs Frigyes , Johnson William L.
Published: March 2008

The reaction of the bulk glass forming alloy Zr41Ti14Cu12Ni10Be23 (Vit 1) with W, Ta, Mo, AlN, Al2O3, Si, graphite, and amorphous carbon was investigated. Vit 1 samples were melted and subsequently solidified after different processing times on discs of the different materials. Sessile drop examinations of the macroscopic wetting of Vit 1 on the discs as a function of temperature were carried out in situ with a digital optical camera. The reactions at the interfaces between the Vit 1 sample and the different disc materials were investigated with an electron microprobe. The structure and thermal stability of the processed Vit 1 samples were examined by x-ray diffraction and differential scanning calorimetry. The results are discussed in terms of possible applications for composite materials.
Synthesis of Copper and Lithium Copper Ferrites as High Magnetization Materials
Authors: Kuehn K. E. , Sriram D. , Bayya S. S. , Simmins J. J. , Snyder R. L.
Published: March 2008

The ferrite with composition Cu0.5Fe2.5O4 was heat treated in air and in reducing atmospheres to different temperatures within the solid solution region confirmed by dynamic high-temperautre x-ray characterization. The samples were quenched in oil and air, and lattice parameter, Curie temperature, and saturation magnetization measurements were completed. The magnetization measurements for these samples showed a maximum 4πMs of 0.7729 and 0.5426 T at 10 and 300 K, respectively. The cationic distribution based on the low-temperature 4πMs measurements is (Cu+0.24Fe3+0.76)A[Cu+0.26Fe3+1.74]BO4 → 4.9 µ B. X-ray-pure Cu0.5Fe2.5O4 samples were also synthesized by slow cooling from the formation temperature to 900 °C in a reducing atmosphere. A temperature–PO2 diagram for the stability of Cu0.5Fe2.5O4 under the conditions of the experiment was determined. Low-temperature 4πMs measurements did not indicate an increase in the Cu+ A site occupancy for the samples cooled to 900 °C in a reducing environment above those samples that were quenched from high temperature. Curie temperatures for all Cu0.5Fe2.5O4 samples ranged from 348 to 369 °C. Lithium additions (0.1 mol/unit formula) to copper ferrite Li0.1Cu0.4Fe2.5O4 decreased the room-temperature 4πMs values to 0.5234 T with a corresponding decrease in the 10 K measurements to 0.7047 T. From the low-temperature magnetization measurements, the distribution was (Cu+0.15Fe3+0.85)A[Cu+0.25Li+0.1Fe3+1.65]BO4 → 4.48 µ B.
Micropipes in Silicon Carbide Crystals: Do all Screw Dislocations have Open Cores?
Authors: Vetter William M. , Dudley Michael
Published: March 2008

Micropipes in a 6H–SiC semiconductor wafer were studied by scanning electron and atomic force microscopy. The screw dislocations intersecting the wafer's surface were located by etch pitting, and their Burgers vectors determined by x-ray topography. The etch pits were eroded into smooth craters by ion beam etching to expose levels of dislocation line from inside the sample's bulk. There a micropipe's diameter is distant from surface relaxation effects. Hollow cores (micropipes) were observed at the base of the craters whose screw dislocations had Burgers vectors of magnitude three multiples of the c-lattice parameter and higher. Screw dislocations with 1c and 2c Burgers vectors had no associated micropipes.
In situ Temperature Measurement During Spray Forming of A2-tool Steel and Axisymmetric Two-dimensional Analysis
Authors: Moon B. C. , Lee Z. H. , White D. R. , Lavernia E. J.
Published: March 2008

An in situ temperature measurement was performed during spraying of A2-tool steel, and the results were used to verify an axisymmetric two-dimensional computer simulation program, which was developed for the prediction of shape and temperature variation in a spray-forming process. A thin thermocouple was placed inside of the chamber in advance and brought to the surface of the deposit during spraying. The temperature was then recorded. The surface temperature of the deposit was also measured by an infrared video camera. The emissivity of the surface of A2-tool steel during spraying was determined to be 0.23 through comparison of the temperatures measured by the thermocouple with the ones measured by the infrared video camera. The heat transfer coefficient at the top surface was estimated by comparing the calculated results with the experimental data. The cooling curve predicted on the basis of the numerical simulation showed good agreement with the experimental data.
Joining of Alumina Ceramics Using Nanocrystalline Tape Cast Interlayer
Authors: Chaim R. , Ravi B. G.
Published: March 2008

Nanocrystalline transition alumina tape casts were used as interlayers to join conventional alumina ceramic pellets. The joining experiments were performed by hot pressing at 1200–1300 °C under uniaxial pressures of 55 and 80 MPa for 1- and 5-h durations, with and without a nanocrystalline interlayer. Successful joints were enabled only above 1250 °C in the presence of the interlayer. Generally, the joint 4-point bending strength increased with the increase in joining temperature, pressure, and duration. The average bending strength of the interface joined at 1250 °C was 245 ± 65 MPa compared to the pellet strength of 268 MPa. Postjoining heat treatments at 1400 °C for 3 h caused reduction in the joint strength. The interlayer at the joint exhibited homogeneous and crack-free microstructure. The changes in the joint strength were discussed with respect to the densification and grain growth behavior of the nanocrystalline interlayer.