bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Modification and Characterization of Plasma Sprayed Alumina Coatings using Lasers
Authors: Krishnan R. , Dash S. , Kesavamoorthy R. , Babu Rao C. , Tyagi A. K. , Raj Baldev
Published: April 2011

A synergetic way of combining superior properties of ceramics with that of metals is to apply ceramic coatings over metallic substrates. Also, ceramic coatings provide better protection of the covered metal under concomitant corrosion and wear conditions. Of all the advanced ceramic materials, Al2O3 is widely used due to its low cost and availability in high purity forms. But the alumina coatings made through Air Plasma Spray suffers from major disadvantages such as presence of metastable γ-Al2O3 phase, high surface roughness and porosities. In this paper, we have shown the feasibility of transforming the γ-Al2O3 phase present in the as-sprayed coatings to a thermodynamically stable α-Al2O3 phase. A continuous wave CO2 laser having maximum power of 500W was used to provide a surface specific heating without affecting the metallic substrate. In addition to XRD, Raman scattering and photoluminescence investigations were carried out using a Ar+ laser to confirm the restoration of alpha phase and the reduction in porosity respectively. Also, 1 mW He-Ne laser operating in TEM00 mode was used to examine the reduction of surface roughness using laser scattering technique. The intensity of the specular reflection was used to quantify the surface roughness. Both reduction in surface roughness and porosity were evaluated using SEM micrographs taken on the surface and cross section of the coatings.
Attenuation of Surface Acoustic Waves by Carbon Nanotubes
Authors: Ciplys Daumantas , Rumyantsev Sergey , Shur Michael S. , Vajtai Robert , Wei Bingqing , Ajayan Pulickel , Gaska Remis , Rimeika Romualdas
Published: April 2011

A strong attenuation of surface acoustic waves in the range of 30 to 100 MHz by singlewalled carbon nanotube layers deposited on the surface of piezoelectric lithium niobate single crystal has been observed. The attenuation exhibits non-monotonous dependence on nanotube density. This attenuation is attributed to the acoustoelectronic interaction between electric fields of the SAW and charge carriers in the nanotubes. The experimental results are in the qualitative agreement with the theory of acoustoelectronic interaction in inhomogeneous structures.
Screen Printing of Carbon Nanotubes for Field Emission Displays
Authors: Yi Mann , Jung Hyuck , Seo Woo-Suk , Park Jong-Won , Chun Hyun-Tae , Koh Nam-Je , Han Soo-Deok , Lee Dong-Gu
Published: April 2011

Carbon nanotubes (CNTs) have been significantly used for the field emitters for display applications. It is necessary to investigate the process variables affecting the screen printing of carbon nanotubes for the fabrication of good-quality field emitter devices with uniformity. Screen printing techniques have some advantages such as the short processing time and lower processing cost. The carbon nanotube pastes for screen printing are normally composed of organic binders, carbon nanotubes, and some additive materials. In this study, the carbon nanotube emitters for field emission displays were fabricated with different processing variables such as paste viscosity, paste composition, screen mesh, etc. The CNT pastes were printed on Cr-coated/Ag-printed soda-lime glass substrates. As a result, the processing variables were optimized for the good screen printing. From the I-V characteristics, the turn-on field of single-walled nanotubes was lower than that of multi-walled nanotubes. The decrease in the mesh number of screen masks resulted in decreasing the turn-on field and increasing the electron emission current due to the higher density and vertical alignment of printed-CNTs.
The nucleation and growth of nano-structured diamond on phosphor and boron ions implanted Si substrates
Authors: Gu C. Z. , Wei L. , Sun Y. , Jia J. K. , Jin Z. S.
Published: April 2011

Nanocrystalline diamond films deposited by microwave plasma chemical vapor deposition (MWPCVD) method were observed on Si substrates implanted with phosphor (P) and boron (B) ions at room temperature via scanning electron microscopy (SEM). The relations between the species, energies and doses of implanted impurities and the nucleation, grain size and morphology of diamond were studied. The results present that different nucleation density from 106 cm-2 to 109 cm-2 can be obtained on implanted and unscratched Si, which is larger of 3–6 magnitude orders than that on mirror-polished Si. The nano-structured diamond films can be deposited on scratched Si substrates implanted by higher concentration of phosphor and boron ions. The grain sizes of nano-structured films can be adjusted by controlling the implanted energies and doses, and nano-structured films can be synthesized with low impressive stress. The Raman spectroscopy was employed to analysis the phase purity of nano-structured film, which shows a broad peak at around 1150 cm-1 relative to the nano-structured and tetrahedrally bonded carbon network.
Modelling of the mechanical and tribological properties of coatings and surface treatments
Authors: Bull S. J.
Published: April 2011

Over the past few years a wide range of coatings and surface treatments have been developed to enhance component performance. Increasingly coating architectures are becoming more complex and multilayer, superlattice and graded coating systems are becoming widely available. This offers so many potential coating variants that it is almost impossible to envisage trying all the possibilities to optimise performance. The need for predictive performance models has never been more acute but model development has generally lagged behind the introduction of new coatings. For tribological coatings the mechanics of contact is particularly important if performance is to be understood. This paper briefly reviews developments in numerical simulation and extends recent modelling developments in an energy-based predictive model for the hardness and Young's Modulus of a coated system. The model predictions can be improved by considering the fracture behaviour of the coating.
A comparative microtribological investigation of diamond-like carbon films for applications in microsystems
Authors: Imad-Uddin Ahmed S. , Bregliozzi Giuseppe , Haefke Henry
Published: April 2011

This study reports on the microfrictional properties under reciprocating sliding of different types of commercially available diamond-like carbon (DLC) films, prepared using low and high frequency plasma-assisted chemical vapor deposition (PACVD) and the vacuum arc method. Silicon and sapphire balls were used as counterbodies. Friction-load curves suggest that, for applied forces in the N to μN regime, two properties have a strong influence on the microfriction: First, the chemical composition plays a dominant role and second, the film roughness. With silicon against DLC, microfriction of hydrogen-free DLC films was greater than the hydrogen containing films. With sapphire counterbodies, microfriction was inversely proportional to film roughness. For all films tested, microfriction was independent of the sliding velocity. Mild wear in the form of scratches was observed only on silicon, while no wear could be detected on any of the DLC films. These results illustrate the utility of implementing microtribological testing in a coating development for microsystems.
Deformation Microstructure Under Nanoindentations in Cu Using 3D X-Ray Structural Microscopy
Authors: Yang Wenge , Larson B. C. , Pharr G. M. , Lepienski C. P. , Ice G. E. , Budai J. D. , Tischler J. Z. , Liu Wenjun
Published: April 2011

We have used a recently developed x-ray structural microscopy technique to make nondestructive, submicron-resolution measurements of the deformation microstructure below a 100mN maximum load Berkovich nanoindent in single crystal Cu. Direct observations of plastic deformation under the indent were obtained using a ∼0.5 μm polychromatic microbeam and diffracted beam depth profiling to make micron-resolution spatially-resolved x-ray Laue diffraction measurements. The local lattice rotations underneath the nanoindent were found to be heterogeneous in nature as revealed by geometrically necessary dislocation (GND) densities determined for positions along lines beneath a flat indent face and under the sharp Berkovich indent blade edges. Measurements of the local rotation-axes and misorientation-angles along these lines are discussed in terms of crystallographic slip systems.
Activation volume analysis of plastic deformation in fcc materials using nanoindentation
Authors: Elmustafa A. A. , Tambwe M. F. , Stone D. S.
Published: April 2011

Activation volumes for plastic deformation of fcc metals are measured using nanoindentation. Materials include bulk, polycrystalline aluminum and α-brass, and sputtered copper and nickel thin films on silicon substrates. From a hardness measurement, V* is defined as 9kBT/∂H/∂ln , where H is the hardness and is a representative strain rate beneath the indenter. Data obtained using nanoindentation are consistent with those obtained using more conventional experiments based on uniaxial loading.
Fracture Behavior of Thin Film PZT on Silicon Mems and Membranes
Authors: Olson A. L. , Skinner J. L. , Bahr D. F. , Richards C. D. , Richards R. F.
Published: April 2011

This research focuses on identifying the fracture mechanism in thin film silicon membranes and PZT on silicon composite structures under static and dynamic loading conditions. Square silicon membranes with a 3mm side-length and thickness between 1.5 and 3.0μm, with and without 1.5μm of PZT, were pressurized to failure while laser interferometry was used to determine the maximum strain at failure. The strain at fracture of silicon membranes, initiating from the sharp corner radius inside the micromachined cavity, was improved from 0.37% to 0.8% by an isotropic etch of the sharp corner. Fracture of PZT on silicon membranes, tested at the mechanical resonant frequency suggested that fracture initiates in the blanket PZT layers under reversed bending. Etching the PZT from high strain regions along the membrane surface improved the strain at failure of the composite device by 40%.
Frictional behavior of C60 monolayer films on graphite (HOPG)
Authors: Okita S. , Matsumuro A. , Miura K.
Published: April 2011

The frictional behavior of a C60 monolayer film between graphite substrates is studied using a homebuilt surface force apparatus. The mean frictional force from the C60 monolayers is estimated to be approximately 2mN, which is one-fifth that of C60 thin films. The C60 monolayer films exhibit a low frictional force of 2mN up to one hundred scans under a normal stress of 8MPa, which indicates that the C60 monolayer film is highly promising for use as a lubricant. Key words, C60 monolayer film, Lubrication, Mechanical properties, Micromachines
Effects of Large Load and Shear Rate Variations on the Friction of a Branched Hydrocarbon Liquid
Authors: Gourdon Delphine , Israelachvili Jacob
Published: April 2011

Shear measurements were performed on mica surfaces with molecularly thin films of squalane confined between them. Squalane is a branched hydrocarbon liquid that can be in the liquid, glassy or liquid-crystalline state under confinement. The friction forces, especially the transitions between smooth and intermittent (e.g., stick-slip) sliding, were measured over a wide range of applied loads and sliding velocities. The results reveal that, depending on the conditions, qualitatively different behavior can arise in the same system. These include both abrupt and continuous transitions, short and very long transient effects, and chaotic or saw-tooth stick-slip. The differences between these branched and simpler molecules are compared, and the results are analyzed in terms of rate-and-state models traditionally used in the analysis of seismic phenomena.
Synthesis and Characterization of Magnetic Polymeric Nanospheres for Biomedical Applications
Authors: Kim D. K. , Mikhaylova M. , Toprak M. , Guyou A. , Jeong Y. K. , Muhammed M.
Published: April 2011

Entrapment of proteins in biodegradable nanospheres has been widely investigated as a technique to produce sustained release formulations for protein or anti-cancer drugs administration. Amphiphilic PLLA-mPEG diblock copolymer was prepared by ring opening polymerization (ROP) to form polymeric nanoparticles with a core-shell structure. The main encapsulation technique done is a water-in-oil-in-water (w/o/w) solvent evaporation technique. Here, protein was encapsulated using a newly developed water-in-oil emulsion-solvent diffusion technique. This technique leads to the formation of an emulsion combined with the immediate precipitation of the PLLA-mPEG. This phenomenon is caused by the diffusion of the polymer solvent to an external organic phase.
Cross-linked Chitosan and Poly(allyl amine) Thin Films
Authors: Schauer Caroline L. , Schoen Paul E. , Ligler Frances S.
Published: April 2011

The alternation of chitin layers with various compounds allows nature to create novel materials with selective refractive properties. Various organisms employ layered materials for survival; for example, in butterflies such materials cause the apparent disappearance and reappearance during flight to evade predators. The selective light refraction is achieved through control of the thickness and index of refraction of the multiple layers. With the ultimate goal of reproducing these layers, thin single films of chitosan, the soluble form of chitin, and poly(allyl amine) have been prepared and their optical properties analyzed. Ellipsometry, reflectance IR, reflectance spectroscopy, SEM and software modeling were used to characterize these films. Possible applications for optical layered materials range from medical diagnostics to environmental monitoring.
Novel Macro and Meso Porous Materials Prepared from Miscible Polysulfone/Polyimide Blends
Authors: Ding Yong , Bikson Benjamin
Published: April 2011

Novel macro and meso porous polysulfone materials were prepared from miscible blends of polysulfones with a phenylindane containing polyimide by chemically decomposing the polyimide phase with a dilute hydrazine solution in methanol. The polyether sulfone meso porous membranes are transparent films, with uniform pore sizes in the range of 30 nm. On the other hand, bisphenol A polysulfone based porous materials are opaque with pore sizes in the range of 200 nm.
Ferrimagnetic Membranes for Separation of Paramagnetic and Diamagnetic Species
Authors: Gwak Jihye , Ayral André , Rouessac Vincent , Cot Louis , Grenier Jean-Claude , Jang Eue-Soon , Choy Jin-Ho
Published: April 2011

For using as separative membranes based on magnetic selectivity, nanoporous ferrimagnetic membranes of maghemite (γ-Fe2O3) and cobalt ferrite (Fe2CoO4) were prepared by the sol-gel route from ferrofluid colloidal solutions. Their magnetic properties were examined by superconductor quantum interference device (SQUID), and their structures and porous textures were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption-desorption analyses. O2-N2 adsorption and air separation experiments were carried out in order to evidence magnetic interactions in static and dynamic conditions, respectively. A small effect of an external magnetic field on the selectivity of these membranes was observed.
Study of the effect of morphology of nanoporous carbon membranes on permselectivity
Authors: Rajagopalan Ramakrishnan , Foley Henry C.
Published: April 2011

The present work is aimed at developing uniform nanoporous carbon membranes on porous stainless steel supports. Thin layers of polyfurfuryl alcohol are applied on the stainless steel supports using spin coating method. Nanoporous carbon is obtained by pyrolyzing polyfurfuryl alcohol films under inert atmosphere. Uniform nanoporous carbon membranes were obtained by repeated spin coating and pyrolysis of polyfurfuryl alcohol on the stainless steel supports. The morphology of the membranes was examined using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). It was shown that there is direct correlation between the morphology and the selectivity of the membranes. SEM and AFM show the presence of globular domains during the formation of carbon membranes. The selectivity increased with the decrease in the size of the globules. It was also shown that the annealing of the membrane affected both the morphology and the selectivity of the membrane.
Pervaporation and Vapor Permeation Characteristics of a Porous SiO2-ZrO2 Membrane for Separation of Organic Solvents/Water Mixtures
Authors: Asaeda Masashi , Tasaka Yasuhumi
Published: April 2011

The sol-gel techniques were applied to fabricate some improved porous SiO2-ZrO2(50%) membranes for separation of organic solvents/water mixtures by pervaporation and vapor permeation methods at the normal boiling points of mixtures such as iso-propanol(IPA)/water and 1-propanol /water mixtures. The porous SiO2-ZrO2 membranes were found quite stable even at a high water content in the feed mixtures. They showed quite large pervaporation fluxes more than 450moles/(m2h) at 73mol% of IPA in the feed, for example, while the water flux for vapor phase separation at the same conditions was around 250mol/(m2h). The separation characteristics of organic chemicals/water mixtures by pervaporation and the vapor permeation methods are largely different in many points. Especially in this work separation by vapor permeation has been studied to compare with that of pervaporation taking into account the vapor-liquid equilibrium characteristics of the mixtures.
Selective Deposition of Pd on Porous Alumina Support Using Supercritical CO2
Authors: Matsukata Masahiko , Nishizuka Takashi , Sekine Yasushi , Kikuchi Eiichi
Published: April 2011

A Pd/α-Al2O3 composite membrane was prepared on a porous α-Al2O3 disk via the thermal decomposition of bis(hexafluoroacetylacetonato)Pd(II), Pd(hfac)2. Pd(hfac)2 was dissolved in supercritical CO2 at 303 K, supplied to the substrate, and thermally decomposed at 403 and 443 K. The decomposition of Pd(hfac)2 at 443 K resulted in a sufficient pore filling of substrate with Pd as well as the formation of a thin Pd top layer. The hydrogen flux through this membrane was about 1.7 times than that of a electro-less plating Pd membrane with about 20 μm thick. Hydrogen permeation was governed by the solution-diffusion mechanism which gave a high separation selectivity.
Biocompatibility of Modified Polyetheretherketone (Peek-Wc) Membranes: Human Plasma Adsorption
Authors: Bartolo Loredana De , Gugliuzza Annarosa , Cirillo Beatrice , Morelli Sabrina , Drioli Enrico
Published: April 2011

Polymeric membranes are widely used in biomedical field for bioartificial organs, medical devices and disposable clinical apparatus. Clinical utilization of blood-contacting devices requires the development of biomaterials with improved blood compatibility. The aim of this work was the exploration of a potential biocompatible membrane derived from a modified polyetheretherketone such as PEEK-WC. The surface affinity of this membrane to human plasma and plasmatic proteins such as albumin, fibrinogen and immunoglobulin G was compared to that of some commercial membranes. Changes with time of the membrane interfacial properties were evaluated by means of contact angle measurements using human protein solutions and human plasma. The extent of plasma protein adsorption on all investigated membranes was measured by comparing the behavior of the different polymer surfaces when contacting the three plasmatic proteins.
Modelling Flocculated Cell Suspensions using a Population Balance Approach: Applications to Microfiltration
Authors: Ranil Wickramasinghe S. , Han Binbing , Akeprathumchai Saengchai , Qian Xianghong
Published: April 2011

Experimental results for flocculation of yeast and CHO cells using cationic polyelectrolytes are presented. These results suggest the existence of a self-similar floc size distribution. The experimentally determined floc size distributions have been modelled using a population balance approach. For flocculated yeast suspensions, the variation of the floc volume fraction with dimensionless particle diameter is predicted by the population balance model assuming a binary fragment distribution function. However, for CHO cell flocs, the floc volume fraction is predicted using a log normal fragment distribution function. Since the efficiency of unit operations such as microfiltration may be improved by flocculation of the feed suspension characterization of the particle size distribution is of great importance.
Elastomeric and nanoporous membranes via Langmuir Blodgett transfer of cross-linked monolayers
Authors: Xu Hui , Heger Robert , Mallwitz Frank , Blankenhagel Marita , Peyratout Claire , Goedel Werner. A.
Published: April 2011

Nanometer thin membranes with considerable application potential in micro mechanics and materials science can be prepared by transferring cross-linked monomolecular layers of polyisoprenes or polyisobutenes with ionic head groups from the water surface to solid substrates with holes. Especially if monolayers of low glass transition polymers are cross-linked, elastomeric membranes are obtained, which might find application in micro mechanical devices like membrane valves and pumps. Incorporation of hydrophobised colloids leads to composite membranes, which can be converted into porous membranes via removal of the colloids.
Structurally Composite Membranes of Titanium Oxide and Titanium Phosphorus Oxide for Proton Conduction at Intermediate Temperatures
Authors: Tsuru Toshinori , Yagi Yasuhito , Kinoshita Yosuke , Yoshioka Tomohisa , Asada Masashi
Published: April 2011

Composite membranes of titanium oxide and phosphorus oxide (TiP) were prepared by the sol-gel method and evaluated for use as proton conductive materials at intermediate temperatures. Titanium phosphorus oxide sol solutions were prepared by the hydrolysis of titanium isopropoxide (TTIP) using hydrochloric acid as a catalyst in isopropanol solutions, and the addition of an appropriate amount of phosphoric acid (H3PO4). A new concept for structurally composite membranes is proposed for proton conductive membranes. A composite membrane, Ti/TiP, where the pores of a porous titanium oxide layer are filled with titanium phosphorus oxide, was found to be effective for high electrical conductivity as well as mechanical strength. Electrical conductivities as high as 0.1 and 0.06 S cm−1 at 100 and 300 °C, respectively, under a partial pressure of water of 50 kPa, was achieved for the Ti/ TiP membranes.
Critical Evaluation of Macroscopic Theories for Multi-Component Diffusion in Ideal Langmuir Sorbents
Authors: Benes Nieck E. , Verweij Henk
Published: April 2011

Materials research involves many areas for which a proper understanding of multi-component mass transport is essential. Examples include sintering and transport-limited reaction in syntheses. In addition, materials may be principally designed for direct manipulation of mass transport, as in membrane materials. Macroscopic descriptions for mass transport are available, but physical interpretation of related transport parameters is generally not straightforward and often relies on microscopic considerations. We will show that, even for diffusion in a simple ideal Langmuir type lattice, macroscopic theories should be used with caution. Differences in mobilities of dissimilar species can set off percolation behavior, causing the flux of the more mobile species to vanish. Such behavior is, for instance, observed for zeolite membranes and cannot be predicted by commonly accepted macroscopic transport theories. Correlations between successive movements of molecules cause a decrease in the self-diffusion coefficient, DS. For non-equilibrium transport it can be shown that correlation effects in most cases disappear in which case non-equilibrium transport becomes related to the component diffusion coefficient D, instead of the smaller DS.
Some Defect Types in Intermetallics and their Consequences
Authors: Cahn Robert W.
Published: April 2011

This short introductory overview focuses on point defects and their practical implications, on antiphase domains, and also on a feature that is not always perceived as a defect – imperfect long-range order. All these defect types have consequences for mechanical behavior of various kinds; imperfect LRO also affects the superconducting behavior of A15s. Other unfamiliar defects in intermetallics, to be outlined, include ‘rattling atoms’ in certain thermoelectric materials. Geometry and dynamics of dislocations in intermetallics are left to other contributors.
Point Defect Mechanisms in Deformation and Phase Transformation of Titanium Aluminide Alloys
Authors: Appel Fritz , Paul Jonathan D.H. , Fröbel Ulrich
Published: April 2011

Point defects in intermetallic compounds are subjected to significant constraints due to the directional bonding, long-range order and off-stoichiometric deviation of the materials. This leads to a variety of defects with distinct differences in morphology, concentration and mobility. In the present study the implications of these defect characteristics on the mechanical properties of two-phase titanium aluminide alloys will be investigated. The major areas of the study are: (i) deformation induced point defects that contribute to work hardening; (ii) dislocation locking due to the formation of defect atmospheres; (iii) transport processes involved in phase transformation and recrystallization occurring during long-term creep. The applied methods include mechanical testing, static strain aging and structural characterisation by high resolution electron microscopy.
A Revised Jogged-Screw Model For Creep Of Equiaxed γ-TiAl: Identification Of The Key Substructural Parameters.
Authors: Karthikeyan Subramanian , Viswanathan Gopal B. , Mills Michael J.
Published: April 2011

A modification of the classic jogged-screw model has been previously adopted to explain observations of 1/2[110]-type jogged-screw dislocations in equiaxed Ti-48Al under creep conditions. The aim of this study has been to verify and validate the parameters and functional dependencies that have been assumed in that model. The original solution has been reformulated to take into account the finite length of the moving jog. This is a better approximation of the tall jog. The substructural model parameters have been further investigated in light of the Finite Length Moving Line (FLML) source approximation. The original model assumes that the critical jog height (beyond which the jog is not dragged) is inversely proportional to the applied stress. By accounting for the fact that there are three competing mechanisms (jog dragging, dipole dragging, dipole bypass) possible, we can arrive at a modified critical jog height. The critical jog height was found to be more strongly stress dependent than assumed previously. The original model assumes the jog spacing to be invariant over the stress range. However, dynamic simulation using a line tension model has shown that the jog spacing is inversely proportional to the applied stress. This has also been confirmed by TEM measurements of jog spacings over a range of stresses. Taylor's expression assumed previously to provide the dependence of dislocation density on the applied stress, has now been confirmed by actual dislocation density measurements. Combining all of these parameters and dependencies, derived both from experiment and theory, leads to an excellent prediction of creep rates and stress exponents.
Creep Properties of a High Niobium Containing γ-TiAl Alloy Sheet Material
Authors: Bartels A. , Bystrzanowski S. , Gerling R. , Schimansky F.-P. , Kestler H. , Weller M. , Clemens H.
Published: April 2011

In this study Ti-46Al-9Nb (at%) sheet material processed by a powder metallurgical route was examined. Subsequent to hot rolling the sheets were subjected to a stress-relief treatment at 1273K for 3 hours. During this heat treatment a fine-grained near gamma microstructure has been formed. 100 hours tensile creep tests under constant load were carried out at 700°C in rolling direction, transverse direction as well as 45° direction. Using the method of load changes a stress exponent of 4.1 was determined. Furthermore, the apparent activation energy was determined in the temperature range of 715 – 775°C. Both stress exponent and activation energy suggest that diffusion assisted dislocation climb is the dominant creep mode. A comparison of these results with those of so-called conventional or so-called “2nd generation” γ-TiAl based alloys, e.g. Ti-46.5Al-4(Cr,Nb,Ta,B) (at%) and Ti-47Al-4(Cr,Mn,Nb,Si,B) (at%), indicates a significantly better creep resistance and a higher activation energy of the high Nb containing alloy. Additionally, internal friction experiments were conducted in order to analyze the deformation behavior under very small strains at elevated temperatures.
Interface Structure and Energy Calculations for Carbide Precipitates in γ-TiAl
Authors: Benedek R. , Seidman D. N. , Woodward C.
Published: April 2011

Ternary carbide precipitates improve the high-temperature creep strength of 2-phase TiAl alloys. The perovskite (P-type) Ti3AlC nucleates at relatively low temperatures (750 deg. C), whereas hexagonal (H-type) Ti2AlC precipitates occur at somewhat higher temperatures. Calculations are performed, based on first- principles-local-density-functional theory, of the interface structure and energy of these two carbides with a 7-TiAl matrix. Calculations are first done on coherent interfaces, and approximate corrections are then made for the effect of misfit. The perovskite is known to form needle-shaped precipitates oriented along the c-axis of the host. Our calculations yield a relatively low energy for the (100) perovskite-host interface, which is a favorable orientation owing to its low misfit, and because the terminating carbide layer for the coherent interface is pseudomorphic with the host. Predictions are given for the critical thickness for coherence and the critical nucleation size for a P-type precipitate. Calculations for interfaces of H-type platelets with the host show a much larger interface energy than that for the P-type precipitate.
Oxygen induced chemical ordering and ultrafine lamellar structure formation in a Ti-48 at. % Al alloy
Authors: Lefebvre Williams , Loiseau Annick , Menand Alain
Published: April 2011

Influence of oxygen on the microstructure development of a Ti-48 at. % Al alloy has been investigated by means of transmission electron microscopy and 1D atom probe. Oxygen is found to significantly increase the temperature of the α → α2 chemical ordering reaction. As a consequence, above a critical oxygen content, the α → α2 transformation is substituted to the α → γm massive transformation when the Ti-48 Al alloy is quenched from the single a-phase field. In such a case, our pervious work has shown that the alloy exhibits a fully (α2 + γ) ultrafine lamellar structure. The present work gives a complete description of the ultrafine lamellar structure formation which, in opposition to the classical lamellar structure formation, involves an intragranular nucleation and growth of the γ phase within the α2 matrix.
Microcrack Nucleation and Crack Propagation in Equiaxed γ TiAl
Authors: Crimp Martin A. , Ng Boon-Chi , Simkin Benjamin A. , Bieler Thomas R.
Published: April 2011

To gain a better understanding of the ductility limitations in TiAl alloys, the mechanisms involved in deformation strain transfer and/or microcrack initiation at grain boundaries have been examined in an equiaxed near-γ alloy. These studies have been carried out on both in-situ and ex-situ deformed bulk samples using scanning electron microscopy (SEM) techniques for both orientation analysis and deformation defect imaging. Selected area electron channeling patterns (SACPs) have allowed determination of grain orientations, eliminating ambiguity between the a and c axes. Deformation twins and dislocations have been imaged in the bulk samples using electron channeling contrast imaging (ECCI). A combination of ECCI contrast analysis and trace analysis based on orientations determined from SACP has allowed identification of the active deformation systems. Microcracks have been found to initiate at γ-γ boundaries as a result of an inability to adequately transfer twin strain from grain to grain. Once initiated, cracks propagate through cleavage and re-nucleation of grain boundary microcracks in front of the advancing crack. A geometric based predictive factor has been developed that accounts for microcrack initiation at γ-γ boundaries based in deformation twinning and strain accommodation by ordinary dislocations.
Microstructural Effect on Environmental Embrittlement of Isothermally Forged TiAl-Based Intermetallic Alloys
Authors: Takasugi T. , Tsuyumu T. , Kaneno Y. , Inoue H.
Published: April 2011

The TiAl-based (Ti-46Al-7Nb-1.5Cr (at%)) intermetallic alloy was tensile tested in vacuum and air as a function of temperature to investigate microstructural effect on the moisture-induced embrittlement. The reduction in tensile strength (or elongation) due to testing in air diminishes as testing temperature increases. From the fracture strength (or elongation)-temperature curves, it was found that the near gamma grain microstructure was most resistant, and the dual-phase microstructure most susceptible to moisture-induced embrittlement. Also, the moisture-induced embrittlement of the TiAl-based intermetallic alloy with fully lamellar microstructure depends on the lamellar spacing, and reduced with decreasing lamellar spacing.
The Heterogeneous Character of Phase Transformations Caused by Limited Vacancy Mobility
Authors: Püschl Wolfgang , Soffa William A. , Pfeiler Wolfgang
Published: April 2011

In homogeneous phase transformations the order parameter proceeds towards equilibrium uniformly in all microvolumes of the system. However, defect-mediated diffusion (vacancy mechanism) involving local atomic jump processes during the early stages of transformation kinetics can produce discrete regions within which the order parameter has changed significantly embedded in an unperturbed matrix. This effect is evident in order-order transformations in B2 FeAl as measured by residual resistivity. An estimate of the heterogeneity regime is calculated in terms of vacancy diffusion parameters.
HRTEM Observation of Partially Ordered Long-Period Superstructures in Al-Rich TiAl Alloys
Authors: Hata S. , Higuchi K. , Mitate T. , Kuwano N. , Itakura M. , Tomokiyo Y. , Nakano T. , Nagasawa Y. , Umakoshi Y.
Published: April 2011

Atomistic microstructures of long-period superstructures in Al-rich TiAl alloys were investigated by high-resolution transmission electron microscopy. The multi-slice image simulation revealed that Al-atoms in Ti-rich (002) layers of the superstructures are imaged as very bright dots under appropriate observing conditions. By enhancing the contrast of the very bright dots using an image processing technique, partially ordered long-period superstructures were clearly characterized. For the short-range order state, A4B, A2B and A3B type ordered-clusters are generated in the Ti-rich (002) layers. These ordered-clusters are in contact with each other, and form local microdomains of various superstructures, such as Al5Ti3, h-Al2Ti and so on. For the Al5Ti3 and h-Al2Ti ordered states, the ordered-clusters are tiled periodically to form the Al5Ti3 or h-Al2Ti domains and characteristic anti-phase boundary structures.
Effect of Antiphase Boundary on the Pseudoelasticity in Fe3Al Single Crystals
Authors: Yasuda Hiroyuki Y. , Nakano Kazuaki , Ueda Masato , Umakoshi Yukichi
Published: April 2011

Pseudoelasticity in Fe3Al single crystals with the D03 structure was investigated focusing on the type of thermally-induced antiphase domain boundaries (APDB) developed in the crystals. Fe3Al single crystals containing 23.0at%Al and 28.0at%Al were produced by a floating zone method. Fe-23.0at%Al single crystals with an appropriate heat treatment demonstrated perfect strain recovery during unloading after compression to plastic strains below 5.0%. In contrast, Fe-28.0at%Al single crystals exhibited little strain recovery. The ordering process and the type of thermal APDB depended strongly on the alloy composition. As a result, B2-type APDB having a displacement vector (R) of 1/4<111> was frequently observed in Fe-23.0at%Al, while D03-type APDB with R=1/2<111> was dominant in Fe-28.0at%Al. In Fe-23.0at%Al, the strong interaction between B2-type APDB and 1/4<111> superpartial dislocations led to the individual motion of the superpartials dragging deformation-induced antiphase boundary (APB). The restoring force due to the deformation-induced APB resulted in the pseudoelasticity in Fe-23.0at%Al single crystals. Moreover, the refinement of antiphase domains surrounded by B2-type APDB was found to be effective in the enhancement of shape recovery in the crystals. Thus, the thermally-induced APDB in the D03 phase played an important role in the pseudoelasticity in Fe3Al single crystals.
Modeling Dislocation Dissociation and Cutting of γ′ Precipitates in Ni-Based Superalloys by the Phase Field Method
Authors: Shen Chen , Mills Michael J. , Wang Yunzhi
Published: April 2011

We incorporate γ-surface data of both γ and γ′ phases from ab initio calculations into the phase field model to study dislocation dissociation and interaction with γ′ particles in Ni-based superalloys. Through three examples we demonstrate the unique capabilities of the model in characterizing the core structure of a dissociated superdislocation in γ′ phase, the creation and annihilation of planar defects such as CSF and APB caused by dislocation cutting through the γ′ phase and the interplay between the cutting and looping mechanisms.
The Role of Cluster Formation on the Magnetic Properties of Nd-Fe-Al-based Magnetic Alloys
Authors: Betancourt I. , Valenzuela R.
Published: April 2011

We present a detailed investigation of the role of the disorder degree on magnetic properties for melt spun and die cast intermetallic Nd-Fe-Al-based alloys. For melt spun alloys, the roll speed was varied between 30 m/s and 5 m/s, which resulted in a clear dependence of coercivity on increasing roll speed, showing a steep decrease (from 250 kA/m to 10 kA/m). The results are interpreted in terms of a gradual transition from fully disordered microstructure (30 m/s sample) to short range ordered one (i.e., a clustered microstructure at 5 m/s), which is a consequence of a diminished cooling rate. On the other hand, die-cast alloy affords cluster formation due to this very low cooling rate compared with the melt spinning process and in consequence, coercivity values of 284 kA/m were observed. Further alloying addition (B, Cu, Dy) on the original Nd-Fe-Al composition, exhibited coercivity enhancement (up to 388 kA/m) due to the presence of small Nd-based crystallites, which act as pinning centers.
Defects Formation in LaNi5-based Alloys Investigated by In-situ X-ray Diffraction
Authors: Nakamura Yumiko , Akiba Etsuo
Published: April 2011

Defects formation in LaNi5-based alloys was investigated by X-ray diffraction (XRD). In-situ XRD data measured along the first hydriding-dehydriding P-C isotherms were analyzed by the Rietveld method. Lattice strain and crystallite size were evaluated from the peak profile. In LaNi5hydride phase formed accompanying with 2 % of anisotropic lattice strain in  direction caused by dense dislocations. Coexisting solid solution phase was not affected by the strain in the hydride phase. Lattice parameterabecame smaller after cycles than before hydriding, which is related with vacancies formation.

Only 5 % of Al substitution for Ni dramatically changed the defects formation behavior. Hydride phase did not show lattice strain in the first hydriding but showed small strain during dehydriding. Formation of both dislocations and vacancies are strongly affected by substitution of other elements for a part of Ni.
Interactions of Mechanical Twinning and Dislocation Glide with Polytwin-Interfaces in L1o-Ordered Iron-Palladium Intermetallics
Authors: Xu Huiping , Wiezorek Jörg
Published: April 2011

The defect structures in polytwinned (PT) FePd have been studied after room temperature deformation by transmission electron microscopy (TEM). Interactions between gliding dislocations and mechanical twins with the {101}-conjugated PT-interfaces have been identified. Based on crystallographic analyses of shear transfer of dislocations and microtwins across the PT-interfaces in FePd boundary reactions have been identified that are consisted with the TEM observations. A model has been proposed, which is suitable to rationalize significant contributions to strain-hardening from these defect-interface interactions in PT-FePd.
Effects of elastic strain energies on a hydride precipitation in LaNi5-based compounds
Authors: Tanaka K. , Inui H. , Yamaguchi M. , Koiwa M.
Published: April 2011

The elastic energies associated with hydride formation have been calculated using coherent elasticity theory. The energies modify the required condition for hydride nucleation to lower temperatures or higher hydrogen gas pressures. Since the elastic energies are quite large, hydride cannot form in a crystal or on a planer surface without assistance of a lattice defect. Hydride can form with reasonable excess hydrogen gas pressure only at a corner of specimen at which the most part of elastic energy is released.
Magnetic Structure and Thermal Expansion of Eu4Ga8Ge16
Authors: Birkedal Henrik , Daniel Bryan J. , Stucky Galen. D. , Christensen Mogens , Iversen Bo B.
Published: April 2011

The orthorhombic clathrate compound Eu4Ga8Ge16 orders antiferromagnetically at about 8 K. The magnetic structure is established by neutron powder diffraction while the thermal expansion and atomic displacement parameters are studied by synchrotron powder diffraction. The Eu spins align along the a-axis and achieve a zero-temperature magnetic moment equivalent to that of the free Eu2+ ion. The thermal expansion is largest along the a-axis while the expansion along c has almost the same magnitude as that along b. The Eu displacement parameters display significant residual values at 0 K, largest in the c direction.
Negative Thermal Expansion
Authors: Sleight Arthur W.
Published: April 2011

Negative thermal expansion behavior has been found in many oxides where oxygen or a cation has a coordination number of two. The MO2, AM2O7, A2M3O12, AMO5, and AO3 families, where A is an octahedral cation, M a tetrahedral cation, and the oxygen coordination is two, have been investigated for their thermal expansion properties. Negative thermal expansion has been found in all families except the AO3 family, where very low thermal expansion was found in the case of TaO2F. Open networks are necessary to allow free transverse thermal motion of oxygen, which is the apparent cause negative thermal expansion in these families. This openness leads to two problems. One is that structure collapse transitions tend to occur as the temperature is lowered. There is little or no thermal expansion below this transition. A solution to this problem is to maintain sufficient ionic character in the bonds holding the network together. The other problem is that when the networks become sufficiently open, they tend to hydrate. This hydration destroys the negative thermal expansion of the network.
Selective Preparation of Nickel Silicides and Germanides Using Elemental Multilayers as Reactive Precursors
Authors: Jensen Jacob M. , Ly Sochetra , Kyablue Xavier , Johnson David C.
Published: April 2011

Using elemental multilayers with designed composition and ultrathin repeating subunits (λ=20 A) we have prepared nickel monosilicide and nickel germanide directly without the formation of any intervening phases. When the same synthetic strategy is used to prepare nickel-silicon-germanium compounds the first nucleated phase is a ternary phase with the NiAs structure.
Oxidation-Protection Methodology for Long-Term use of Carbon-Carbon Fiber-Matrix Composites in Oxidizing Ambients
Authors: Golecki Ilan , Fuentes Karen , Walker Terence
Published: April 2011

A methodology is described for protecting Carbon-Carbon fiber-matrix composite (C-C) components from oxidation for extended use in oxidizing ambients for lifetimes of the order of 10,000 hours, from room temperature to 650°C. This time-temperature profile is relevant to applications such as airborne heat exchangers. Weight changes of oxidation-protected, pitch-fiber based C-C coupons in flowing dry air at 650°C are presented. Two types of external protective approaches are compared: (a) multi-phase, borophosphate-based fluidizing overseal coatings applied directly to C-C, and (b) the same overseal coatings applied to CVD SiOxCy coated C-C. The latter, dual-coating approach provides an effective engineering solution for the above temperature-time profile and is particularly applicable to thin (0.1–3 mm thick), complex-shaped articles. The behavior of inert substrates (oxidized silicon) with the same overseal coatings is compared to the behavior of the C-C substrates. This approach can be applied with optional modifications to suit other environmental conditions, and other carbon-containing materials, such as carbon foams and C-SiC composites.
Synthesis and Characterization of New Iron and Zinc Phosphate Materials with Open Framework
Authors: Song Yanning , Chernova Natasha A. , Zavalij Peter Y. , Stanley Whittingham M.
Published: April 2011

Open framework materials are of great interest due to the applications in the fields of adsorption, ion exchange, molecular sieving and catalysis. Metal phosphates are very important open framework materials due to the rich crystallography. Several new iron phosphate materials have been synthesized and characterized in our lab. Two new iron (III) phosphates, FePO4, have been synthesized from careful dehydration of hydrothermally prepared monoclinic and orthorhombic hydrated phosphates FePO4·2H2O. Reversible insertion and extraction of lithium into new iron phosphate hydroxide materials with 3-d rod-packing framework shows it to be an excellent intercalation material. Several other transition metals are also incorporated successfully into these compounds without changing the structure. With ethylenediamine as template, 1-D chain, 2-D layered and 3-D network iron phosphate materials were synthesized. The structure, electrochemical and magnetic properties of these compounds were studied. Meanwhile, two new zinc phosphates with methylammonium templates were also synthesized. There are infinite Zn-O-Zn chains in one of the compounds, while closed 4-member circuits made up from Zn-O-Zn linkage present in the other.
Temperature-Dependent Magnetic Properties of SiO2-Coated Ni75Fe25 Nanoparticles
Authors: Wu Mingzhong , Zhang Y.D. , Hui S. , Ge Shihui
Published: April 2011

SiO2-coated Ni75Fe25 nanoparticles were prepared using a wet chemical method and their structure and magnetic properties were investigated using x-ray diffraction, high-resolution transmission electron microscopy, and a superconducting quantum interference device magnetometer. The SiO2 material was in an amorphous state. The Ni75Fe25 nanoparticles were in a simple cubic state and contained inner oxide (Ni-oxide and Fe-oxide) cores whose size decreased with increasing calcination temperature. The nanoparticles were basically in the ferromagnetic state. Their saturation magnetization increased with increasing calcination temperature, whereas their coercivity decreased with increasing calcination temperature. The nanoparticles exhibited strong temperature-dependent magnetic behaviors. The Bloch exponent fell from 1.5 for the bulk to smaller values and decreased with increasing oxide content, while the Bloch constant was much bigger than that for bulk and increased significantly with oxide content. The value of coercivity decreased with increasing temperature, and this decrease was more pronounced for the nanoparticles containing high oxide content. The exchange anisotropy arising from the exchange coupling across the Ni75Fe25/oxide interfaces was examined and was used to interpret the observed temperature-dependent behaviors.