bluuebunny/crossref_metadata_2025 huggingface dataset:
Paradox of Strength and Ductility in Metals Processed Bysevere Plastic Deformation
Authors: Valiev R. Z. , Alexandrov I. V. , Zhu Y. T. , Lowe T. C.
Published: March 2008

It is well known that plastic deformation induced by conventional forming methodssuch as rolling, drawing or extrusion can significantly increase the strength of metalsHowever, this increase is usually accompanied by a loss of ductility. For example, Fig.1 shows that with increasing plastic deformation, the yield strength of Cu and Almonotonically increases while their elongation to failure (ductility) decreases. Thesame trend is also true for other metals and alloys. Here we report an extraordinarycombination of high strength and high ductility produced in metals subject to severeplastic deformation (SPD). We believe that this unusual mechanical behavior is causedby the unique nanostructures generated by SPD processing. The combination ofultrafine grain size and high-density dislocations appears to enable deformation by newmechanisms. This work demonstrates the possibility of tailoring the microstructures ofmetals and alloys by SPD to obtain both high strength and high ductility. Materialswith such desirable mechanical properties are very attractive for advanced structuralapplications.
Study of Stresses in Thin Silicon Wafers with Near-infraredphase Stepping Photoelasticity
Authors: Zheng Tieyu , Danyluk Steven
Published: March 2008

This paper reports on a study of stress in thin silicon plates sectioned from wafers by a near-infrared transmission technique. Phase stepping was incorporated to determine the magnitude and orientation of stress from fractional birefringence fringe images. The anisotropic relative optic-stress coefficient of (100) silicon was determined and the limitation of the stress orientation measurement is discussed.
Joining of Ti3SiC2 with Ti–6Al–4V Alloy
Authors: Gao N.F. , Miyamoto Y.
Published: March 2008

The joining of a Ti3SiC2 ceramic with a Ti–6Al–4V alloy was carried out at the temperature range of 1200–1400 °C for 15 min to 4 h in a vacuum. The total diffusion path of joining was determined to be Ti3SiC2/Ti5Si3Cx/Ti5Si3Cx + TiCx/TiCx/Ti. The reaction was rate controlled by the solid-state diffusion below 1350 °C and turned to the liquid-state diffusion controlled with a dramatic increase of parabolic rate constant Kp when the temperature exceeded 1350 °C. The TiCx tended to grow at the boundarywith the Ti–6Al–4V alloy at a higher temperature and longer holding time. TheTi3SiC2/Ti–6Al–4V joint is expected to be applied to implant materials.
Electrochemical and Thermal Properties of Hydrogen-absorbed Mg67Ni28Pd5 Amorphous Alloy
Authors: Yamaura Shin-Ichi , Isogai Keita , Kimura Hisamichi , Inoue Akihisa
Published: March 2008

We have examined electrochemical properties and thermal stability of the amorphous Mg67Ni28Pd5 alloy produced by melt-spinning subjected to electrochemical hydrogen charge. In the cyclic life test, the discharge capacity of the alloy increases significantly with increasing cycle number and reaches 411 mA h/g at the 15th cycle. Thehydrogen-absorbed amorphous alloy crystallizes through two stages of primarycrystallization of Mg2Ni, followed by precipitation of Mg2NiH4 at the second stage.The completed crystallization temperature of the hydrogen-absorbed alloy increases by 65 K as compared with the as-solidified one. It is thus concluded that stability of theMg-based amorphous alloy against crystallization increases by hydrogen absorption.
High-strain-rate Superplastic Flow in 6061 Al Composite Enhanced by Liquid Phase
Authors: Kim W.J. , Hong S.H. , Jeong H.G. , Min S.H.
Published: March 2008

High-strain-rate superplastic behavior of powder-metallurgy processed 0%, 10%, 20%,and 30% SiC particulate reinforced 6061 Al composites was studied over a range of temperatures from 430 to 610 °C. The strength of the 6061 Al composites was lowerthan that of the 6061 Al matrix alloy in the temperature range where grain boundarysliding is believed to control the plastic flow. The difference in their strength was alsoobserved to be temperature dependent, increasing with increase in temperature.Abnormally high activation energy for superplastic flow was another important featureof the 6061 Al composites. These behaviors in particle weakening and activationenergy have strong resemblance to those noted in the high-strain-rate superplastic 2124Al composites studied previously. The observed particle weakening was attributed toliquid-enhanced superplastic flow and discussed by adopting the concept of effectivediffusivity considering mass flow through liquid phase formed at the solute-segregatedregion near SiC/Al interfaces.
Negative Transverse Magnetoresistance of Boron-doped Graphite at Liquid-nitrogen Temperature in Relation to 3D Weak Localization
Authors: Hishiyama Y. , Matustani T. , Suzuki M. , Kaburagi Y. , Sugihara K.
Published: March 2008

The negative transverse magnetoresistance of boron-doped graphite at liquid-nitrogen temperature has been studied in detail using 3000 °C-treated Grafoil(commercially available graphite foil), with the measurements of interlayer spacingd002 at room temperature, the Hall coefficient and electrical resistivity at liquid-nitrogen temperature, and temperature dependence of the resistivity in a temperature range 1.7–273 K. The negative transverse magnetoresistance can be measured for the specimens with hole carriers having the Fermi energy lower than −0.07 eV, estimatedby the Slonczewski–Weiss–McCure (SWMcC) band model using the Hall coefficient data. Characteristic feature of the negative transverse magnetoresistance has been investigated in terms of the SWMcC band model and a weak localization theory obtained by extending Kawabata's theory.
Bunching of Surface Steps and Facet Formation on Analumina Surface
Authors: Ravishankar N. , Barry Carter C.
Published: March 2008

The behavior of steps on the basal surface of alumina under conditions of evaporativemass transport has been investigated. Steps on a clean surface of alumina tend to be uniformly spaced indicating a repulsive interaction between the steps. The presence of foreign particles causes step bunching that leads to the formation of a new facet. The lower energy of the macrofacet may provide a driving force for the bunching process.
Tert-butylamine and Allylamine as Reductive Nitrogen Sources in Atomic Layer Deposition of TaN Thin Films
Authors: Alén Petra , Juppo Marika , Ritala Mikko , Leskelä Markku , Sajavaara Timo , Keinonen Juhani
Published: March 2008

The atomic layer deposition technique was used to deposit TaN thin films from TaCl5 and TaBr5 and tert-butylamine or allylamine as a reductive nitrogen source with and without ammonia. The films were characterized with time-of-flight elastic recoil detection analysis, energy-dispersive x-ray spectroscopy, x-ray diffraction, and the standard four-point probe method. The films deposited from tert-butylamine and ammonia with both tantalum precursors had reasonably low halide contents. When allylamine was used as a nitrogen source, on the contrary, the films contained larger amounts of chlorine and other impurities. The resistivity increased markedly as the deposition temperature was decreased. The lowest resistivities (below 1500 μΩ cm) were obtained when the films were deposited from TaCl5 or TaBr5 with tert-butylamine at 500 °C.
Fabrication of Nanoporous Ceramic Thin Films: De-alloying and Self-organized Template Formation Onamorphous Substrates
Authors: Paulose Maggie , Varghese Oomman K. , Grimes Craig A.
Published: March 2008

Sol-gel-derived metal oxide ceramic thin films deposited onto amorphous iron-rich substrates were found to form self-organized nanoporous structures dependent upon the extent to which the substrate is de-alloyed, a function of the substrate alloycomposition, acid concentration of the sol, and film drying conditions. Field emission scanning electron microscopy, transmission electron microscopy, and x-ray energy dispersive analysis were used to investigate details of the porous structure formation.Our studies showed the more electrochemically active elements in the amorphous substrate are de-alloyed by the sol in high-humidity environments, whereupon the liberated elements form oxides replicating the de-alloyed substrate matrix resulting in athree dimensional porous network structure.
Ductile-to-brittle Transition in Superplastic Silicon Nitride Ceramics
Authors: Zhan Guo-Dong , Mitomo Mamoru , Xie Rong-Jun , Kurashima Keiji
Published: March 2008

The ductile-to-brittle transition was observed in a superplastic silicon nitride nanoceramic. This transition depends on strain rates and deformation temperatures. Generally, the material exhibits ductility at low strain rates and high deformation temperatures. At 1600 °C, the material is brittle when the strain rates are higher than 10−3/s. At a fixed strain rate of 10−3/s, the material exhibits brittleness when the temperatures are lower than 1550 °C. Moreover, critical strain rate for the brittle to ductile transition depends on deformation temperature. The critical strain rates increase with increases in the deformation temperature. When the deformation temperature is 1700 °C, the critical strain rates reach a maximum at 10−2/s. The extent of superplastic deformation in the present material was found to be limited not by intergranular cavitation but by the initiation and growth of surface cracks.
Synthesis of Cu47Ti34Zr11Ni8Bulk Metallic Glass by Warm Extrusion of Gas Atomized Powders
Authors: Sordelet D.J. , Rozhkova E. , Huang P. , Wheelock P.B. , Besser M.F. , Kramer M.J. , Calvo-Dahlborg M. , Dahlborg U.
Published: March 2008

Cu47Ti34Zr11Ni8amorphous gas atomized powders were consolidated by warm extrusion. After consolidation near 723 K using an extrusion ratio of 5, the material retains between 88% and 98% of the amorphous structure found in the gas atomized powder. The onsets of the glass transition and crystallization temperatures of this extruded material are observed respectively at slightly higher and lower temperatures than those of the starting powders. These temperature shifts are attributed to a composition change in the remaining amorphous phase during partial devitrification throughout the extrusion process. Powders extruded at the same temperature, but using higher extrusion ratios of 9 and 13, exhibit substantial devitrification during the consolidation process yet still deform homogeneously.
Study of Microstructure in SrTiO3/Si by High-resolution Transmission Electron Microscopy
Authors: Yang G. Y. , Finder J. M. , Wang J. , Wang Z. L. , Yu Z. , Ramdani J. , Droopad R. , Eisenbeiser K. W. , Ramesh R.
Published: March 2008

Microstructure in the SrTiO3/Si system has been studied using high-resolution transmission electron microscopy and image simulations. SrTiO3 grows heteroepitaxially on Si with the orientation relationship given by (001)STO//(001)Si and [100]STO//[110]Si. The lattice misfit between the SrTiO3 thin films and the Si substrate is accommodated by the presence of interfacial dislocations at the Si substrate side. The interface most likely consists of Si bonded to O in SrTiO3. The alternative presentation of Sr and Si atoms along the interface leads to the formation of 2× and 3× Sr configurations. Structural defects in the SrTiO3 thin film mainly consist of tilted domains and dislocations.
Synthesis of Silicon Carbide Films from Partially Oxidized Polyvinylsilane by Carbon Tetrachloride Solution Casting
Authors: Narisawa Masaki , Hasegawa Takeshi , Okamura Kiyohito , Itoh Masayoshi , Apple Thomas , Moraes Kevin V. , Interrante Leonard V.
Published: March 2008

Polyvinylsilane (PVS), derived from vinylsilane by radical polymerization, was partially oxidized in hot carbon tetrachloride solution by flowing air. If the air flow time is adjusted, soft gel films can be formed in a Teflon dish by casting the PVS solution. After the PVS films were peeled from the substrates, they were pyrolyzed at various temperatures. Spectroscopic studies of the pyrolyzed films up to 1273 K suggested that carbosilane (Si–CH2–Si) structures are formed in the films at 473–673 K. The compositions of the amorphous films obtained at 1673 K were approximately SiC1.38O0.21 and SiC1.41O0.51, depending on the crosslinking conditions. The oxygen incorporated in the films was removed in the form of CO and SiO during further heating at 1673–1873 K. The compositions of the films were changed to approximately SiC1.25 and SiC1.26, respectively, at 2073 K. The films obtained at 1273 K did not show degradation during the oxidation at 1273–1673 K while a protective silica layer was formed on their surfaces.
Fracture Toughness and Adhesion Energy of Sol-gel Coatings on Glass
Authors: Toonder Jaap Den , Malzbender Jürgen , With Gijsbertus De , Balkenende Ruud
Published: March 2008

The reliability of coatings that are used in industrial applications critically depends on their mechanical properties. Nanoindentation and scratch testing are well-established techniques to measure some of these properties, namely the elastic modulus and hardness of coatings. In this paper, we investigate the possibility of also assessing the coating fracture toughness and the energy of adhesion between the coating and the substrate using indentation and scratch testing. Various existing and new methods are discussed, and they are illustrated by measurements on particle-filled sol-gel coatings on glass. All methods are based on the occurrence of cracking, and they are therefore only applicable to coating systems that act like brittle materials and exhibit cracking during indentation and scratching. The methods for determining the fracture toughness give comparable results, but the values still differ to within about 50%. The values of the adhesion energy obtained from different measurements are consistent, but it remains uncertain to which extent the obtained values are quantitatively correct. The results show that the methods used are promising, but more research is needed to obtain reliable quantitative results.
Interface Mobility Under Different Driving Forces
Authors: Mendelev M. I. , Srolovitz D. J. , Shvindlerman L. S. , Gottstein G.
Published: March 2008

We used an Ising model to determine whether boundary mobility is an intrinsic material parameter or if it depends on the nature of the driving force for boundary migration. The simulations included both capillarity and external field-driven boundary migration. The external field-driven, flat boundary simulations showed that boundary mobility depends strongly on boundary inclination at low temperature but not at high temperature. On the other hand, the boundary mobility in capillarity-driven migration shows no dependence on boundary inclination and is independent of the boundary migration geometry. An initially circular grain shrinks as a circle and a half-loop boundary retracts with profiles predicted under the assumption that the boundary mobility is isotropic during capillarity-driven migration even when the temperature is very low and the external-field-driven boundary migration is extremely anisotropic. However, when an external field is superimposed on the capillarity driven migration of the circular boundary, the circular grain exhibits well-defined corners consistent with the simulation lattice symmetry. In this case, the boundary mobility is much different than if the external field were omitted. This is a clear demonstration that the boundary mobility can depend on the nature of the driving force for boundary migration.
Active Metal Brazing for Reliable Ceramic Joints Using TiN Coating
Authors: Yoon Chulsoo , Kim Tae Woo , Seo Osung , Kang Shinhoo
Published: March 2008

To improve the strength of brazed joints, a TiN-coated layer was introduced as an interlayer and reaction barrier for ceramic-ceramic joints. Al2O3, Si3N4, and ZrO2 ceramics were brazed with a Ag–Cu–In–Ti alloy after a TiN coating was applied on the ceramic substrates. The strength of as-brazed and thermally treated Al2O3 specimens with a TiN coating was found to be equivalent to that of bulk Al2O3. However, the Si3N4 and ZrO2 systems showed a significant reduction in joint strength. The difference in the strength can be explained on the basis of the bond strength of the coating, the reaction products, and residual stress developed at the joint interfaces.
Effect of Cu concentration on the interfacial reactions between Ni and Sn–Cu solders
Authors: Chen W. T. , Ho C. E. , Kao C. R.
Published: March 2008

The eutectic 99.3Sn–0.7Cu solder (wt%, Sn–0.7Cu) is the most promising lead-free replacement for the eutectic Sn–Pb solder in wave-soldering applications. In this study, the effect of a small perturbation in the Cu concentration on the reaction between the Sn–0.7Cu solder and Ni was investigated. Specifically, four Sn–xCu solders (x = 0.2, 0.4, 0.7, and 1) were reacted with Ni at 250 °C. A slight variation in Cu concentration produced completely different reaction products. When the Cu concentration was low (x = 0.2), the reaction product was (Ni1–xCux)3Sn4. At high Cu concentrations (x = 0.7 and 1), the reaction product was (Cu1–yNiy)6Sn5. When the Cu concentration was in-between (x = 0.4), both (Ni1–xCux)3Sn4 and (Cu1–yNiy)6Sn5, formed. The above findings were rationalized using the Cu–Ni–Sn isotherm. The results of this study imply that the Cu concentration must be strictly controlled in industrial production to produce the desired intermetallic at the interface.
Morphology, kinetics, and thermodynamics of solid-state aging of eutectic SnPb and Pb-free solders (Sn–3.5Ag, Sn–3.8Ag–0.7Cu and Sn–0.7Cu) on Cu
Authors: Lee T. Y. , Choi W. J. , Tu K. N. , Jang J. W. , Kuo S. M. , Lin J. K. , Frear D. R. , Zeng K. , Kivilahti J. K.
Published: March 2008

Intermetallic compound (IMC) growth during solid-state aging at 125, 150, and 170 °C up to 1500 h for four solder alloys (eutectic SnPb, Sn–3.5Ag, Sn–3.8Ag–0.7Cu, and Sn–0.7Cu) on Cu under bump metallization was investigated. The samples were reflowed before aging. During the reflow, the solders were in the molten state and the formation of the IMC Cu6Sn5 in the cases of eutectic SnPb and Sn–3.5Ag had a round scallop-type morphology, but in Sn–0.7Cu and Sn–3.8Ag–0.7Cu the scallops of Cu6Sn5 were faceted. In solid-state aging, all these scallops changed to a layered-type morphology. In addition to the layered Cu6Sn5, the IMC Cu3Sn also grew as a layer and was as thick as the Cu6Sn5. The activation energy of intermetallic growth in solid-state aging is 0.94 eV for eutectic SnPb and about 1.05 eV for the Pb-free solders. The rate of intermetallic growth in solid-state aging is about 4 orders of magnitude slower than that during reflow. Ternary phase diagrams of Sn–Pb–Cu and Sn–Ag–Cu are used to discuss the reactions. These diagrams predict the first phase of IMC formation in the wetting reaction and the other phases formed in solid-state aging. Yet, the morphological change and the large difference in growth rates between the wetting reaction and solid-state aging cannot be predicted.
Novel understanding of the YBa2Cu3O7–x thin film growth
Authors: Huang D. X. , Nakamura Y. , Yamada Y. , Hirabayshi I.
Published: March 2008

By combining the cross-sectional observation of the randomly oriented film areas and the analyses of the film microstructural influence by the substrate-surface morphology, we achieved a novel understanding of the YBa2Cu3O7–x (YBCO) thin film growth process, which leads to an explanation of different microstructures formed in YBCO thin films. Selective and competitive growth of YBa2Cu3O7–x and Ba–Cu–O/Cu–O was found to occur in the whole film growth process depending on the local surface roughness in which the interfacial energy played a controlling role.
Preparation and characterization of SiO2–B2O3–P2O5 particles and films generated by flame hydrolysis deposition for planar light-wave circuits
Authors: Shin Hyungsoo , Yi Ji- Hyun , Baek Jong-Gab , Choi Mansoo
Published: March 2008

Boron-phosphosilicate glass particles were deposited on Si wafer by flame hydrolysis deposition under controlled conditions. A few ten nanometer sized and spherical glass particles were synthesized in an oxy-hydrogen flame. The wafer surface temperature of 500 °C proved sufficient to form the Si–O–B framework while a higher temperature (approximately 730 °C) was required to produce Si–O–P formation. Gaussian bands at 3242 cm−1 provided evidence that the dissolved B2O3 concentration increased with the substrate temperature. In as-deposited porous films, a certain quantity of crystalline B2O3 remained, which was completely transformed into the noncrystalline phase after post deposition annealings. Film density measurements indicated that the B2O3 content in the doped silica films would be substantially lower than that in the precursor mixture.
Nitride-bonded silicon nitride from slip-cast Si + Si3N4 compacts
Authors: Rao R. Ramachandra , Kannan T. S.
Published: March 2008

The dispersability of Si and Si3N4 powders in aqueous media was monitored by particle-size distribution, sedimentation behavior, viscosity/rheological studies, and electrokinetic behavior [zeta potential (ZP) analysis] as a function of pH of their slips. The pH values of 4 and 8 for Si and 10 for Si3N4 resulted in optimum dispersion, characterized by minimum in sedimentation height, minimum in viscosity, and maximum in ZP. The optimum slips of Si + Si3N4 mixtures conditioned in the pH range 8 to 10 were slip cast to obtain green compacts having a density in the range of 59% to 66% theoretical value. When nitrided, these compacts yielded nitride-bonded Si3N4 products having a density of 2.06 to 2.28 g cm−3, Si3N4 bonding phase of 20–60%, and 3-point flexural strength values in the range of 50 to 150 MPa. The microstructure consisted of very fine particles as well as fibrous or whiskerlike α–Si3N4 binding phase enveloping the matrix Si3N4, in total consisting of 90% α–Si3N4 and the rest being β–Si3N4 phase.
Raman spectroscopy and conductivity measurements on polymer-multiwalled carbon nanotubes composites
Authors: Stéphan Christophe , Nguyen Thien Phap , Lahr Bernd , Blau Werner , Lefrant Serge , Chauvet Olivier
Published: March 2008

Thin films of poly(methyl methacrylate)–multiwalled nanotubes composites were produced by spin coating using different nanotube concentrations. The materials were characterized by scanning electron microscopy, energy-dispersive x-ray analysis, and Raman spectroscopy to obtain information on the possible interactions between the constituents and to control the homogeneity of the films. Electrical conductivity measurements of the composites, as a function of the nanotube concentration, show a percolation threshold at very low concentration. Also, the J–E characteristics exhibits a nonlinear behavior at low concentration, becoming linear far above the threshold.
Electrochemical self-assembly of Cu/Cu2O nanowires
Authors: Kenane S. , Piraux L.
Published: March 2008

Arrays of Cu/Cu2O nanowires were grown by electrodeposition in the nanopores of track-etched polymer membranes. If an appropriate solution is used, the electrode potential spontaneously oscillates during the application of a constant cathodic current. Both the period of the oscillations and the composition of the nanowires can be controlled by varying the applied current density. A nanocomposite of copper and cuprous oxide is deposited at an applied current over which oscillations occur. In contrast, pure Cu or Cu2O nanowires are obtained at a deposition current out of the range of oscillation. Electrical transport measurements were also performed on these nanowires.
Surface characterization of carbon fibers by inverse gas chromatography at low pressures
Authors: Rubio J. , Rubio F. , Fierro J. L. , Gutierrez M. C. , Oteo J. L.
Published: March 2008

Carbon fiber surfaces were analyzed by inverse gas chromatography (IGC) and x-ray photoelectron spectroscopy (XPS). IGC measurements were carried out at infinite and finite dilution by using neutral and specific probes. At infinite dilution the dispersive component of the surface free energy and the acid–base indexes were obtained. At finite dilution the energy distribution functions were calculated. Three carbon fibers were analyzed, one untreated and two fibers treated with different sizings. The fibers have similar dispersive components of surface free energy but their acid–base characteristics are markedly different. The untreated fiber has an acidic surface, and the sized fibers have a surface with high base character. The energy distribution functions show different peaks assigned to active sites existing on the carbon fiber surfaces. The use of acid or basic probes provides different energy distribution functions with good correlation with the base and acid character of the fiber surface. Changes in surface heterogeneity revealed by energy distribution functions were correlated also with surface chemical composition derived from high-resolution XPS measurements.
Characterization of (0.4)Pb2(In,Nb)O6:(0.6)Pb(Mg1/3Nb2/3)O3 relaxor ceramics
Authors: Baba-kishi K. Z. , Tai C. W. , Wang J. , Choy C. L. , Chan H. L. W. , Bhalla A. S.
Published: March 2008

The results of the development and characterization of a new relaxor ceramic with nominal composition (x)Pb2(In,Nb)O6(1 − x)Pb(Mg1/3Nb2/3)O3 solid solution with x = 0.4 are reported. The structural characteristics, including the long-range and short-range order, forbidden reflections, and the existence of mixed ordering, were studied by transmission electron microscopy. The most prominent microstructural feature of this compound, which has composition variations in the micro- and nano-regions, was investigated. The presence of the pyrochlore phase and the complex arrangement of inclusions that originate from processing are illustrated. The electrical characteristics of the compound including pyroelectric, piezoelectric, electrostrictive and hysteresis properties are reported. Notable properties of the compound include a reduced hysteresis loop and nonlinear behavior at high field.
Phase transition behaviors of BaTiO3–BaZrO3 solid solutions under high direct current bias fields
Authors: Wada S. , Adachi H. , Kakemoto H. , Chazono H. , Mizuno Y. , Kishi H. , Tsurumi T.
Published: March 2008

The dielectric properties of the Ba(Ti1–xZrx)O3 (BT1–xZx) ceramics with various compositions were investigated under various DC bias fields. In BT0.94Z0.06 ceramics, the dielectric constants (ε) vs temperature (T) curves without DC bias showed no frequency dependence. Its DC bias dependence exhibited that with increasing DC bias fields, the dielectric constants were suppressed while phase transition peaks slightly shifted to high temperature. In BT0.58Z0.42 ceramics, the ε vs T curves without DC bias showed a broad peak with a clear frequency dependence, which revealed that BT0.58Z0.42 ceramics were the relaxor. Its DC bias dependence exhibited that with increasing DC bias fields, the dielectric constants were suppressed while the phase transition peak largely shifted to low temperatures. In BT0.79Z0.21 ceramics, the ε vs T curves without DC bias showed a broad peak without frequency dependence. Its DC bias dependence revealed that the dielectric peak shifted to high temperature and broadened with increasing DC bias. To explain the above phenomena, it was considered that the role of Zr ions on BT1−xZx ceramics is to make the depth of the potential well shallow successively.
Deposition of fine silicon carbide relics by electrostatic atomization of a polymeric precursor
Authors: Grigoriev D. A. , Edirisinghe M. J. , Bao X.
Published: March 2008

A solution of a polymeric precursor for silicon carbide (SiC) was subjected to electrostatic atomization in the cone-jet mode to spray droplets on a zirconia substrate. The resulting deposit was heated to 1300 °C to obtain SiC relics. Precursor and ceramic relics were characterized by microscopy. The size distribution of the droplet relics was studied at several flow rates of the solution to the electrostatic atomization chamber. The results show that by controlling the flow rate SiC relics approximately 5 μm in diameter can be produced.
Sliding friction and wear behavior of Al–Ni–Co–Si quasicrystalline coatings deposited by the high-velocity oxy-fuel spraying technique
Authors: Fleury Eric , Kim Yu-Chan , Kim Jae-Soo , Ahn Hyo-Sok , Lee Sang-Mok , Kim Won-Tae , Kim Do-Hyang
Published: March 2008

The sliding friction and wear performance of Al–Ni–Co–Si quasicrystalline coatings deposited by the high-velocity oxy-fuel technique were investigated under dry sliding conditions. This study indicated that changes in the imposed sliding test conditions modified the friction and wear behavior of quasicrystalline coatings. Qualitative analysis of the contact interface and wear debris were performed with the aim of understanding the role of the third body on the friction and wear processes. The dependence of the coefficient of friction on the sliding velocity and counterpart material was explained by the stick-slip behavior. It was also shown that test conditions favorable for the formation of thick intermediate layers and the densification of the coating subsurface led to low wear rates. Large cylindrical particles, formed by agglomeration of small wear debris, were suggested as a beneficial factor for the reduction of the coefficient of friction.
Influence of BaO Addition on the Phase Formation Characteristics in Li2O–Al2O3–ZnO–SiO2–TiO2–ZrO2 Glass
Authors: Sung Yun-Mo
Published: March 2008

The effect of BaO addition on the crystallization of Li2O–Al2O3–ZnO–SiO2–TiO2– ZrO2 (LAZSTZ) glass was investigated and discussed. The crystallization temperature of BaO-added LAZSTZ precursor glass (LBAZSTZ) was decreased due to the increase in the number of broken ionic bonds, while the transparency of the glass–ceramic was maintained. The lowered activation energy for crystallization in LBAZSTZ glass strongly supports the increase in the number broken bonds. During heating LBAZSTZ glass, phase separation did not occur most probably due to the competition between metal cations having a certain degree of ionic field strength. The formation of β-spodumene as a major phase in LBAZSTZ glass–ceramic was identified using x-ray diffraction.
Synthesis of Superhard and Elastic Carbon Nitride Films by Filtered Cathodic Vacuum arc Combined with Radio Frequency Ion Beam Source
Authors: Cheng Y. H. , Tay B. K. , Lau S. P. , Shi X. , Qiao X. L. , Chen J. G. , Wu Y. P. , Sun Z. H. , Xie C. S.
Published: March 2008

Superhard and elastic carbon nitride films with hardness and elastic recovery of 47 GPa and 87.5%, respectively, were synthesized by using a double-bend filtered cathodic vacuum arc combined with radio-frequency nitrogen ion beam source. The bombardment of energetic nitrogen atom onto the growing film surface results in the high atomic ratio of N/C (0.4), which contributes to the high sp2 content and the formation of a five-membered ring structure in the carbon nitride film at room temperature. The buckling of the five-membered ring basal planes may facilitate cross-linking between the planes through sp3 coordinated carbon atoms. A rigid three-dimensional network is formed, which contributes to the high hardness and elastic recovery of the deposited films.
Prediction of Possible Metastable Alloy Phases in an Equilibrium Immiscible Y–Mo System by ab initio Calculation
Authors: Kong L. T. , Liu J. B. , Liu B. X.
Published: March 2008

In the equilibrium immiscible Y–Mo system, the total energies of the possible structures for YMo3 and Y3Mo metastable phases were calculated as a function of their lattice constants, by employing the Vienna ab initio simulation package, and the results suggested that the D019, L12, and L60 structures were three possible metastable states in the system. Experimentally, hcp and fcc YMo3 metastable phases were obtained in the Y–Mo multilayers driven far from equilibrium by ion irradiation. Moreover, the lattice constants determined by diffraction analysis were in agreement with the predicted values.
Creep of Lanthanum Gallate
Authors: Luecke William E. , Armstrong Timothy R.
Published: March 2008

Strontium- and magnesium-doped lanthanum gallate (LSGM) was deliberately prepared to give A-site deficient nonstoichiometry with compositions (La0.9Sr0.1)z(Ga0.8Mg0.2)O3-δ (z = 1.0, 0.98, and 0.95). Creep tests in four-point bending for 950 °C < T < 1350 °C and 15 MPa < σ < 75 MPa in air demonstrated that all three compositions shared a common stress dependence, n= 1.49 ± 0.10, and a common apparent activation energy, Q = 426 ± 9 kJ/mol. Despite this agreement, the creep rates of the different compositions depended on grain size in different ways: p = 3.1 ± 0.2 for z = 0.98, and p = 1.9 ± 0.1 for z = 0.95. The measured apparent activation energy, Q, for creep is similar, though statistically significantly smaller, than that measured in another LSGM. Both are nearly twice as large as reported activation energies for cation impurity diffusion. The absolute magnitude of the creep rates, after correction for grain size, were 30 to 100 times slower than in another LSGM of similar composition.
Ultraviolet Photoluminescence from 4H–SiC Nanocrystalline Films Deposited on Silicon Substrate
Authors: Fu Zhengping , Yan Beifang , Liu Ruchuan , Ruan Yaozhong
Published: March 2008

Preferred-orientated 4H–SiC nanocrystalline films on silicon substrates were successfully prepared by the pyrolysis of the polyimide Langmuir–Blodgett films containing nanometer-sized amorphous silicon nitride powders. Fourier-transform infrared spectra revealed 4H–SiC nanoparticles with interfacial silicon oxide. Ultraviolet photoluminescence with energies above the band gap of bulk 4H–SiC was observed from the films in which the mean size of 4H–SiC particles was 10 nm, while no photoluminescence was observed from the films in which the mean size of particles was 17 nm. A quantum confinement/luminescence center model is suggested to explain the origin of the ultraviolet luminescence.
Preparation of Fine-grained BaTiO3Ceramics by Spark Plasma Sintering
Authors: Takeuchi Tomonari , Capiglia Claudio , Balakrishnan Nalini , Takeda Yasuo , Kageyama Hiroyuki
Published: March 2008

Dense BaTiO3ceramics consisting of fine grains were prepared using fine powder (average grain size of 0.06 μm; BT006) as a starting material and the spark plasma sintering (SPS) method. The powder was densified to >95% of theoretical x-ray density by the SPS process, and the average grain size of the resulting ceramics was <0.5 μm; the particle size of the initial powder significantly affects the grain size of the resulting SPS pellets. Fixed-frequency (100 kHz), room-temperature permittivity measurements of the BT006-SPS ceramics showed relatively low values (3000–3500) compared with those (typically 5000) for SPS ceramics consisting of larger grains (approximately 1 μm). Lower permittivity was attributed to poor development of ferroelectric domains in the ceramics, which originated from incomplete development of the tetragonal structure as well as the presence of a local orthorhombic structure.
Grain Growth, Stress, and Impurities in Electroplated Copper
Authors: Brongersma S. H. , Kerr E. , Vervoort I. , Saerens A. , Maex K.
Published: March 2008

The widely observed secondary grain growth in electroplated Copper layers is shown to be incomplete after the sheet resistance and stress of the layer appear to have stabilized. Instead the layer is in an intermediate state with a grain size distribution that depends on the plating conditions. Further extensive annealing at high temperatures results in an additional considerable enlargement of the grain structure, accompanied by an additional decrease of the sheet resistance and desorption of impurities that were incorporated during plating.
Grain Morphology of Intermetallic Compounds at Solder Joints
Authors: Choi Won Kyoung , Jang Se-Young , Kim Jong Hoon , Paik Kyung-Wook , Lee Hyuck Mo
Published: March 2008

The grain morphology of the intermetallic compound (IMC) that forms at the interface between liquid solders and solid-metal substrates was observed at solder joints. Cu6Sn5 grains on Cu substrates were rough or rounded, and Ni3Sn4 grains on Ni substrates were faceted. Through the energy-based calculations, the relationship between the IMC grain morphology and Jackson's parameter α was explained. The Jackson's parameter of the IMC grain with a rough surface is smaller than 2 while it is larger than 2 for faceted grains.
Electric Field Enhanced Synthesis of Nanostructured Tantalum Carbide
Authors: Graeve Olivia A. , Munir Zuhair A.
Published: March 2008

Nanocrystalline TaC was synthesized by the field-activated combustion method. The crystallite size ranged from about 30 to 55 nm, depending on the applied field. At low fields (8.54 ≤ E < 16.39 V cm−1) the average crystallite size was relatively unaffected by the field, but it showed a significant increase at fields higher than 16.39 V cm−1. From temperature measurements, this field was found to coincide with the melting of Ta. The combustion wave velocity likewise showed a significant increase when the temperature was at the melting point. The composition of the product showed a dependence on the magnitude of the applied field. At low field values (above a threshold) the product contained Ta2C. When synthesized at high fields, the product showed the presence of TaC phase only. The lattice parameter and the C/Ta ratio showed a slight dependence on the field, both increasing with an increase in the magnitude of the field.
Development and Evolution of Texture in Mg–Zr Alloy Deposited by Physical Vapor Deposition
Authors: Garcés G. , Adeva P.
Published: March 2008

The development and evolution of texture in a Mg–10.6%wt Zr deposit obtained by physical vapor deposition was studied. The deposit exhibits a microstructure characterized by elongated grains with the [0001] direction parallel to the deposit growth direction. The volume fraction of the basal plane component increases throughout the thickness from 45% at the collector side up to around 70%. The minimization of interfacial energy of (0001) planes induces the initial texture at the earliest stage of the deposit formation. Furthermore, the increase in the volume fraction of the (0001) component during deposit growth is provoked by texture competition, which results in the development of grains with the [0001] direction parallel to the deposit growth direction.
Reactions at the Interface Between Al2O3–SiO2 Ceramics with Additives of Alkaline-earth Oxides and Liquid Al–Si Alloy
Authors: Oliveira M. , Agathopoulos S. , Ferreira J. M. F.
Published: March 2008

The interfacial reactions between aluminosilicate ceramics doped with MgO, CaO, or BaO and Al–7 wt% Si alloy were investigated at 1023, 1173, and 1323 K under vacuum for 4 h. Alkaline-earth oxide additives defined phase formation and microstructure of the sintered ceramics and subsequently controlled the ceramic/metal interfacial reactions, which were always intensive. In general, reaction zones consisted of Al2O3, infiltrated with Al. In the case of CaO- and BaO-doped ceramics, precipitates formed into the metal phase and concentrated the reduced Ca and Ba, respectively. A reaction mechanism is proposed, which anticipates an active role of SiO2.
Magnetic Anisotropy of Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.7 Ribbons Produced by Melt Spinning
Authors: Yan A-Ru , Sun Zhi-Gang , Han Baoshan , Shen Bao-Gen
Published: March 2008

A high degree of texture was observed in melt-spun Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.7 ribbons prepared by single-roller melt spinning at low wheel speed; their easy magnetization axis was parallel to the ribbon plane. Magnetization studies showed an obvious magnetic anisotropy and a 90% higher remanance in ribbons for the field parallel to the longitudinal direction (8.5 kGs) than that for the field parallel to the wide direction (4.4 kGs); this was attributed to a dendritic structure of needle-size grains (2–3 × 10–40 μm) with their long axis parallel to the ribbon plane. This texture allowed the development of a new process for producing anisotropic permanent magnets. The domain structure was studied by magnetic-force microscope. A highly ordered and strip-shaped magnetic domain structure was observed on the surface of the ribbons. This was due to the preference for tetragonal c-axis orientation parallel to the surface of melt-spun ribbons. We calculated the domain wall energy γ and critical single-domain particle size Dc of Sm(Co0.68Fe0.22Cu0.08Zr0.02)7.7 ribbons.
Diffuse Phase Transition in Epitaxial BaTiO3 Thin Films
Authors: Chattopadhyay Soma , Teren A. R. , Hwang Jin-Ha , Mason T. O. , Wessels B. W.
Published: March 2008

The thickness dependence of the dielectric properties of epitaxial BaTiO3 thin films was investigated for thicknesses ranging from 15 to 320 nm. The films were deposited by low-pressure metalorganic chemical vapor deposition on (100) MgO substrates. The relative dielectric permittivity and the loss tangent values decreased with decreasing thickness. High-temperature dielectric measurements showed that with decreasing film thickness, the ferroelectric-to-paraelectric transition temperature decreased, the relative dielectric permittivity decreased, and the phase transition was diffuse. The c/a ratio also decreased with decreasing film thickness. The observed behavior for epitaxial films of BaTiO3 was attributed to the presence of strain in the films.
Synchrotron X-ray Diffraction Study of Ba4.5Nd9Ti18O54 Microwave Dielectric Ceramics at 10–295 K
Authors: Tang C. C. , Roberts M. A. , Azough F. , Leach C. , Freer R.
Published: March 2008

The structure of ceramic Ba4.5Nd9Ti18O54 was investigated by synchrotron x-ray powder diffraction from 10 to 295 K. Reitveld refinement and Le Bail profile analysis were applied to the data. Based on an orthorhombic structure, unit cell parameters of a = 22.3479(3) Å, b = 7.6955(1) Å, and c = 12.2021(2) Å were obtained at room temperature and a = 22.3367(5) Å, b = 7.6738(1) Å, and c = 12.1842(3) Å at 10 K. No evidence was found for any major structural change from 10 to 295 K. Within the tungsten bronze framework the two pentagonal channels were fully occupied by Ba; the remaining Ba atoms shared the rhombic channels with Nd. Thermal expansion of the unit cell was found to be anisotropic. The largest expansion occurs along the b cell edge, and the least along the a cell edge. It is proposed that the anisotropy is due to enhanced bending of the TiO6 polyhedra chains along the b direction.
In vacuo Pulsed Laser Ablation of YBa2Cu3O7–x Target for the Formation of Y2O3 Nanostructures
Authors: Jan D. B. , Jia Q. X. , Hawley M. E. , Browne G. W. , Wetteland C. J. , Sun H. P. , Pan X. Q.
Published: March 2008

The formation of superconducting YBa2Cu3O7–x (Y123) by in situ pulsed laser deposition from a stoichiometric Y123 target typically requires an oxygen-ambient environment (P ˜ 100–300-mtorr O2) and appropriate substrate temperature during deposition. We have found that pulsed laser deposition from a Y123 target in vacuo onto a (001) LaAlO3 substrate favors the formation of Y2O3. We observed that the Y2O3 (001) films yield three-dimensional nanoscale morphologies that are markedly different from the planar growth surface of conventional superconducting c-axis Y123 films and Y2O3 films formed from the pulsed laser ablation of a Y2O3 target.
Plastic Flow Instabilities of L12 Ni3(Si,Ti) Alloys at Intermediate Temperature
Authors: Honjo H. , Kaneno Y. , Inoue H. , Takasugi T.
Published: March 2008

The serrated plastic flow of L12 Ni3 (Si,Ti) alloys at intermediate temperature was investigated by tensile tests in terms of the effects of temperature, strain rate, composition, and microstructure. Serrated plastic flow was most strongly observed at 473 K and at a strain rate of 1.6 × 10–4 s–1. Correspondingly, the maximum stress amplitude and the lowest (negative) strain-rate sensitivity were observed at 473 K. Serrated plastic flow took place irrespective of boron doping and was more significant in a fine-grained Ni3 (Si,Ti) alloy. The static aging at 473 K resulted in reduced flow stress. The activation energy for serrated plastic flow was estimated to be about 57 kJ mol–1, suggestive of being smaller than that for lattice diffusion of solutes. The serrated plastic flow behavior of Ni3 (Si,Ti) alloys was compared with that of L12 Co3Ti alloys, and is qualitatively explained on the basis of the dynamics of solutes in the core of a dissociated screw dislocation.
Grinding Assistance in the Transformation of Gibbsite to Corundum
Authors: Torres Sánchez Rosa M. , Boix A. , Mercader R. C.
Published: March 2008

After gibbsite was milled for 5 min in a Cr-steel oscillating mill, corundum was obtained by heating the powder for 3 h at 800 °C. We found that iron contamination, produced by the milling process, is essential to attain the transformation at this low temperature and is located at the surface of the gibbsite particles. The knowledge of the oxidation state and location of the contaminant elements, necessary to control the solid-state reactions and/or phase transformations induced by the milling, was realized in this work by a characterization performed by chemical analysis, x-ray photoelectron spectroscopy, Mössbauer spectroscopy, and isoelectric point determination. The iron contamination amounted to about 3% (as Fe2O3) for the sample milled for 60 min. That the iron contamination that occurred mainly on the gibbsite amorphous surface was concluded after a comparison of the isoelectric point determination of the milled samples with that of a mechanical mixture of gibbsite and hematite. X-ray diffraction studies showed that gibbsite looses its crystallinity after the first 5 min of milling.
Low-temperature chemical synthesis of nanocrystalline KTiOPO4
Authors: Lia Donglin , Wang Zhihong , Zhang Liangying , Yao Xi , Zhou Haoshen
Published: March 2008

Nanocrystalline KTiOPO4 powders were prepared through a chemical process. This process involved the hydrolysis of KOOCCH3 · 2H2O, Ti(OC4H9)4, and PO(OR)3 to produce a homogeneous solution. A gel was formed by the partial evaporation of this solution. After the gel was decomposed at 450 °C, white amorphous powder remained. On calcinating up to 550 °C, the amorphous powder began to transform into nanocrystalline KTiOPO4 powders with an average particle size of 30–50 nm. The KTiOPO4 powders were investigated through x-ray diffraction, infrared spectroscopy, and transmission electron microscopy studies.
Stability of single-wall carbon nanotubes under hydrothermal conditions
Authors: Swamy S. Srikanta , Calderon-Moreno Jose Maria , Yoshimura Masahiro
Published: March 2008

The stability of single-wall carbon nanotubes under hydrothermal conditions (100 MPa pressure, from 30 min to 48 h in the temperature range from 200 to 800 °C) has been investigated. The resultant products were characterized by Raman spectroscopy, x-ray diffraction, and transmission electron microscopy. The stability range of single-wall carbon nanotubes (SWCNTs) under hydrothermal conditions suggests that they, similar to fullerenes, can only survive mild and short-term treatment in high-temperature, high-pressure water. SWCNTs gradually transform into multiwall carbon nanotubes (MWCNTs) and polyhedral graphitic nanoparticules. After 48 h at 750 °C only the Raman spectra characteristic of graphitic carbon were observed. Transmission electron microscopy revealed that after 800 °C and 48 h of treatment SWCNTs fully transformed into MWCNTs and polyhedral carbon nanoparticles.
Preparation and oxidation of Al4SiC4
Authors: Yamamoto Osamu , Ohtani Motoko , Sasamoto Tadashi
Published: March 2008

Single-phase Al4SiC4 was successfully synthesized by heating the powder mixture of aluminum, silicon, and carbon black in the molar ratio corresponding to the chemical composition of Al4SiC4 with a small amount of triethanolamine (TEA) above 1200 °C in argon gas. Without TEA, two phases of Al4C3 and SiC were formed, irrespective of the heating temperature. The marked mass gain by oxidation of Al4SiC4 was observed with forming Al2O3 and SiO2 in the range of 850 to 1150 °C, which slightly increased above 1150 °C. At 1600 °C, mullite was formed by the reaction between Al2O3 and SiO2.