bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Method to Study the Weak Molecular Movements at Nanometric Scale in Low Mobility Materials
Authors: Neagu Eugen R. , Dias C.J. , Lança M.C. , Inácio Paulo , Marat-Mendes José N.
Published: January 2010

For the characterization of the new materials and for a better understanding of the connection between structure and properties it is necessary to use more and more sensible methods to study molecular movement at nanometric scale. This paper presents the experimental basis for a new electrical method to study the fine molecular movements at nanometric scale in dielectric materials. The method will be applied for polar and non-polar materials characterization. Traditionally, the electrical methods used to study the molecular movements are based on the movements of the dipoles that are parts of the molecules. We have proposed recently a combined protocol to analyze charge injection/extraction, transport, trapping and detrapping in low mobility materials. The experimental results demonstrate that the method can be used to obtain a complex thermogram which contains information about all molecular movements, even at nanoscopic level. Actually during the charging process we are decorating the structure with space charge and during the subsequent heating we are observing an apparent peak and the genuine peaks that are related to charge de-trapping determined by the molecular movement. The method is very sensitive, very selective and allows to determinate the parameters for local and collective molecular movements, including the temperature dependence of the activation energy and the relaxation time.
Medium Electric Field Electron Injection/Extraction at Metal-Dielectric Interface
Authors: Neagu Eugen R. , Dias C.J. , Lança M.C. , Igreja Rui , Marat-Mendes José N.
Published: January 2010

The isothermal charging current and the isothermal discharging current in low mobility materials are analyzed either in terms of polarization mechanisms or in terms of charge injection/extraction at the metal-dielectric interface and the conduction current through the dielectric material. We propose to measure the open-circuit isothermal charging and discharging currents just to overpass the difficulties related to the analysis of the conduction mechanisms in dielectric materials. We demonstrate that besides a polarization current there is a current related to charge injection or extraction at the metal-dielectric interface and a reverse current related to the charge trapped into the shallow superficial or near superficial states of the dielectric and which can move at the interface in the opposite way that occurring during injection. Two important parameters can be determined (i) the highest value of the relaxation time for the polarization mechanisms which are involved into the transient current and (ii) the height of the potential barrier W0 at the metal-dielectric interface. The experimental data demonstrate that there is no threshold field for electron injection/extraction at a metal-dielectric interface.
Optimization of Ageing Parameters of a Low Nickel Maraging Steel
Authors: Cabeza M. , Castro Regal Gemma , Merino P. , Pena G. , Román M. , Semiao Javier , Vázquez P.
Published: January 2010

In the present work the age hardening parameters of a 14Ni (200) maraging steel are studied in order to optimize mechanical properties of the steel. The initial characterization of the as received solution annealed steel has been carried out by optical and scanning electron microscopy (LOM and SEM), and hardness measurements. To identify the structural changes during ageing, differential scanning calorimetry (DSC) tests were performed. Different time-temperature combinations were considered for the precipitation hardening treatment of as-quenched material samples. After hardness measurements, three of these treatments were selected for an in depth study. The obtained microstructure at the maximum hardness peaks then analysed (LOM, SEM and TEM) and mechanical behaviour (strength, toughness and wear resistance) was studied for the final selection of the age hardening conditions.
Effect of Heat Treatment on the Corrosion Behaviour of a Mg-Y Alloy in Chloride Medium
Authors: Carboneras M. , Munez Claudio , Rodrigo Pilar , Escalera M. Dolores , López Maria Dolores , Otero Enrique
Published: January 2010

Corrosion behaviour of a Mg-Y alloy (commercial WE54) has been studied. This alloy presents excellent retention of mechanical properties and corrosion resistance at elevated temperatures, a combination of properties that can be of interest in many technology applications. To evaluate the effect of heat treatment on the corrosion resistance, WE54 samples in extruded state and after T6 heat treatment were studied. Corrosion behaviour was evaluated by electrochemical and immersion tests in 3.5 wt.% NaCl solution at room temperature and neutral pH. Surface examination was carried out by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD). It was found that corrosion resistance of the magnesium alloy WE54 in chloride medium was improved by applying the heat treatment to the material, a fact that was correlated with the developed microstructure in T6 condition.
EBSD Study of Grain Boundary Evolution after Different Cold Rolling Reduction in Duplex Steel
Authors: Brisset François , Baudin Thierry , Jura J.
Published: January 2010

The microstructure evolution of a two-phase austenitic-ferritic steel after hot rolling and cold rolling (reduction amounts: 20, 40, 60 and 80%) is investigated with the help of the FEG-SEM / EBSD technique. Special phases orientation relationships (Bain, K-S, N-W and G-T) evolution between neighbouring grains of  and  phases have been characterised as a function of the cold rolling reduction. As this later increases fraction of these particular phase orientation relationships decrease. The same evolution is noticed for the 3 grain boundaries inside the  phase. These results are compared to those observed by TEM.
Morphologies of Widmanstätten Structures and Mechanism Formation in Steels
Authors: Radu Tamara , Constantinescu Simona , Vlad M.
Published: January 2010

This paper presents a research concerning the equilibrium of ferrite and secondary cementite and Widmanstätten structure formation, resulting in precise conditions. If all researchers agree with the mechanisms of ferrite and massive cementite formation in steels, the Widmanstätten structure formation is rather disputable and new data in the area of massive transformation might account for the formation of Widmanstätten structures in the low carbon steels. For the massive phase and Widmanstätten structures, the mathematic relations regarding the rate of growth are presented.
Cellular Microstructure and Mechanical Properties of a Directionally Solidified Al-1.0wt%Fe Alloy
Authors: Goulart Pedro R. , Spinelli J.E. , Bertelli F. , Osório Wislei R.R. , Cheung Noé , Garcia Amauri
Published: January 2010

Upward directional transient solidification experiments have been carried out with an Al-1.0wt%Fe alloy. Tensile tests were carried out with samples collected along the casting length and these results have been correlated with measured cell spacings, since cellular growth has prevailed along the directionally solidified casting. The resulting mechanical properties include ultimate tensile strength, yield tensile strength and elongation. The used casting assembly was designed in such a way that the heat was extracted only through the water-cooled system at bottom of the casting. During non-equilibrium solidification, typical of DC (direct chill) castings, different cooling rates occur from the casting cooled surface up to the top of the casting, causing the formation of metastable intermetallic phases (AlmFe, Al6Fe, etc) in addition to the stable Al3Fe phase. The extensive presence of plate-like Al3Fe phase in the as-cast structure adversely influences the mechanical properties of Al-Fe alloys, since this morphology is more likely to induce microcracks than the fibrous Al6Fe phase. In order to permit an appropriate characterization of these intermetallic phases, they were extracted from the aluminum-rich matrix by using a dissolution technique. These phases were then investigated by optical microscopy and SEM techniques. It was found that the ultimate tensile strength, the yield strength and the elongation increase with decreasing cell spacing and experimental laws correlating cell spacing and these mechanical properties have been established.
Precipitation Kinetics of Aluminium Nitride in Austenite in Microalloyed HSLA Steels
Authors: Radis Rene , Kozeschnik Ernst
Published: January 2010

In this work, the thermodynamic information on aluminium nitride formation and experimental precipitation kinetics data are reviewed. A revised expression for the Gibbs energy of AlN is developed with special emphasis on microalloyed steel. Using the software package MatCalc, computer simulations of AlN precipitation kinetics are performed and compared to several independent experimental results from literature. To mimic the geometrical arrangement of AlN precipitates along austenite grain boundaries, a new model for precipitation at grain boundaries is used, which takes into account fast short-circuit diffusion along grain boundaries as well as the slower bulk diffusion of atoms from inside the grain to the grain boundaries. This is essential for the calculation of AlN precipitation in austenite where nucleation occurs predominantly on grain boundaries. By studying the AlN precipitation at grain boundaries numerically, and by comparison with experimental data, it is demonstrated that the precipitation kinetics of AlN differs significantly from the simulated precipitation kinetics of randomly distributed precipitates assuming spherical diffusion fields.
Textural Modifications during Recovery in Ti-Rich Ni-Ti Shape Memory Alloy Subjected to Low Level of Cold Work Reduction
Authors: Paula Andersan S. , Mahesh Karimbi Koosappa , Schell Norbert , Braz Fernandes Francisco Manuel
Published: January 2010

In shape memory alloys (SMA), the texture can be an interesting factor influencing the anisotropic physical and mechanical characteristics during the phase transformations. It is well known that the texture significantly influences the stress-strain curve and shape memory strain of NiTi SMA. The aim of the present experiment was to analyze the textural modifications in the Ti-rich Ni-Ti SMA after annealing at moderate (500°C for 30 min) and subsequent low level of cold work reduction (10% thickness reduction). The textural results were obtained by X-Ray Diffraction (XRD) during thermal cycling in three points: (i) at room temperature (B19’ phase, after cold work), (ii) at 180°C (B2 phase), and (iii) at room temperature (B19’ phase, after cooling from 180°C). The phase transformations were characterized by Differential Scanning Calorimetry (DSC) and XRD.
Microstructural Evolution Modelling of Nickel Base Superalloy during Forging
Authors: Thébault Julien , Solas Denis , Fandeur Olivier , Baudin Thierry , Rey Colette
Published: January 2010

In order to obtain a better understanding of mechanisms governing the microstructural evolution of nickel base superalloys during forging, experimental and numerical studies have been undertaken. For the experimental part, isothermal compression tests were performed at 1100°C for several ratio and strain rates to reproduce microstructural evolution during industrial forging. The resulting microstructures were analysed by Electron Back Scattered Diffraction method and Transmission Electron Microscopy to identify the dynamic recrystallization mechanisms. In parallel, numerical studies has been carried out in which a crystalline plasticity modelling implemented in the finite element code Abaqus® coupled to a recrystallization Cellular Automaton code was used to simulate forging. The first model allows us to obtain the local mechanical fields (strain, stress, crystallographic orientation, dislocation density …) and the second one predicts the dynamic recrystallization.
A Study of Point Defects in the B2-Phase Region of the Fe-Al System by Mössbauer Spectroscopy
Authors: Hanc Aneta , Kansy Jerzy
Published: January 2010

In this work, Mössbauer spectroscopy and X-ray powder diffraction (XRD) are used in a study of point defect formation in intermetallic phases of the B2 structure of the Fe-Al system as a function of Al concentration. The results are compared with the concentrations of point defect determined from positron annihilation data. In the Mössbauer effect, two types of samples are investigated: Fe-Al alloys with few additives obtained by induction melting and Al-rich metallic powders produced by the self-decomposition method and intensive grinding of high energy in the electro-magneto-mechanical mill. The work presents the values of the 57Fe isomer shift and quadruple splitting for the components describing the point defect in the local environment of a Mössbauer nuclide. The concentration of the Fe vacancies and Fe atoms substituting Al (Fe-AS) are determined. The results show that an increase in Al content causes an increase in vacancy and Fe-AS concentration.
Consolidation of Cu-nDiamond Nanocomposites: Hot Extrusion vs Spark Plasma Sintering
Authors: Nunes Daniela , Livramento Vanessa , Correia Jose Brito , Hanada Kotaro , Carvalho Patrícia Almeida , Mateus R. , Shohoji Nobumitsu , Fernandes H. , Silva C. , Alves Eduardo , Osawa Eiji
Published: January 2010

Due to their interesting properties copper-based materials have been considered appropriate heat-sinks for first wall panels in nuclear fusion devices. The concept of property tailoring involved in the design of metal matrix composites has led to several attempts to use nanodiamond (nDiamond) as reinforcement. In particular, nDiamond produced by detonation has been used to reinforce copper. In the present study, powder mixtures of copper and nDiamond with 20 at. % C were mechanically alloyed (MA) and consolidated via hot extrusion or spark plasma sintering (SPS). The hardness evolutions as well as the structural characterization of as-milled nanocomposite powders and consolidated samples are reported. Density measurements indicate that the consolidation outcome varies significantly with the process used. Transmission electron microscopy (TEM) inspection of the extrusion consolidated sample revealed bonding at the interface between copper and nDiamond particles. The nDiamond size distribution was determined from TEM observations. The results obtained are discussed in terms of consolidation routes.
Synthesis of Carbon Nanotubes on Zeolite Substrate of Type ZSM-5
Authors: Kordatos K. , Ntziouni A. , Trasobares S. , Kasselouri-Rigopoulou V.
Published: January 2010

The present work deals with the synthesis of carbon nanotube-zeolite composites using as method the catalytic liquid spray pyrolysis. The nanotubes were formed after pyrolysis of toluene on the surface of a zeolite of type ZSM-5, which was used as a catalytic substrate. ZSM-5 zeolite was synthesized using the autoclave process and full characterized. Prior to the pyrolyses, the catalytic substrates were produced by mixing a certain amount of zeolite with a solution of Fe(NO3)3•9H2O of specific concentration. The obtained materials from the spray pyrolysis were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetry-differential analysis (TG-DTA).
Light-Induced Functionalization of Amphiphilic Block Copolymers: Application to Nanoparticles for Drug Targeting
Authors: Pourcelle Vincent , Marchand-Brynaert Jacqueline
Published: January 2010

Photografting of bifunctional photolinker on biocompatible amphiphilic copolymers, such as PCL-b-PEGs and PLGA-b-PEGs, has been developed as a practical and versatile strategy for the materials functionalisation. Depending on the copolymer nature (block length, % of crystallinity) and the experimental conditions we could selectively direct the grafting on the hydrophilic PEG segments. The resulting copolymers were further derivatized with molecules of interest (RGD-peptides, LDV-peptides, “home-made”peptidomimetics, mannose derivatives,…) by substitution of the O-succinimidyl ester of the photolinker. The derivatization rates were controlled by radiolabelling, colorimetric assay and XPS spectroscopy. The functionalized copolymers were used in the formulation of nanoparticles displaying the ligands on their outer-shell. This nanoparticulate system was successfully employed for the oral vectorisation of antigen and for the targeted delivery of an anticancer drug.
Tri-Block Copolymers Obtained by RAFT Polymerization: A Promising Material for Drug-Delivery Systems
Authors: Tebaldi M.L.D.S. , Chaparro T.C. , Santos A.M.
Published: January 2010

Tri-block copolymer with pH- and thermo-responsive consisting of poly(t-butylacrylate) and poly(vinylcaprolactam), (PtBA/PVCL) were prepared by RAFT polymerization and characterized by gel permeation chromatography (GPC) and 1H NMR. PtBA and PVCL were used as macro chain-transfer agents (MCTA) to synthesize PtBA-b-PVCL-b-PtBA and/or PVCL-b-PtBA-b-PVCL, which after partial hydrolysis led to amphiphilic tri-block copolymers P(tBA-co-AA)-b-PVCL-b-P(tBA-co-AA) and/or PVCL-b-P(tBA-co-AA)-b-PVCL.
Tuning Active Magnetorheological Elastomers for Damping Applications
Authors: Boczkowska Anna , Awietjan Stefan F.
Published: January 2010

Magnetorheological elastomers (MREs) were obtained by mixing soft polyurethane and carbonyl-iron particles. The effect of the volume fraction of the ferromagnetic particles on the MREs microstructure and properties, as well as their arrangement in relation to the external magnetic field were investigated. As a ferromagnetic component carbonyl–iron powder, with particle size from 6-9µm, was used. The amount of the carbonyl iron particles was varied from 1.5 to 33.0 %(v/v). The samples were produced with randomly dispersed and aligned carbonyl iron particles. Scanning electron and light microscopy techniques were used for the MRE microstructure observations. The rheological properties (G’, G’’ and tan δ) of the MRE were tested without and with the application of the magnetic field. It was found that the microstructure of MREs, particularly the amount and arrangement of the carbonyl-iron particles, has a significant influence on their rheological and damping properties.
Role of Ultraviolet Absorbers (UVA) and Hindered Amine Light Stabilizers (HALS) in ABS Stabilization
Authors: Santos Raquel , Botelho Gabriela , Machado Ana Vera
Published: January 2010

The present work evaluates the combination effect of hindered amine light stabilizers (HALS) and ultraviolet absorbers (UVA) on the ultraviolet (UV) stability of acrylonitrile-butadiene-styrene (ABS). Thus, two types of light stabilizers, Tinuvin P and Chimassorb 119 FL, were used to improve the ABS endurance against UV. Stabilized ABS samples were submitted to accelerated weathering in a Xenontest 150 S chamber, according to standard methods, in order to predict copolymer lifetime within a commercially acceptable time period. Infrared spectroscopy with attenuated total reflectance accessory (FTIR-ATR) was used to follow chemical modifications that occur on the material surface as a consequence of degradation process. While non-stabilized ABS samples loose the butadiene component in the first 22 h of exposure, in stabilized samples submitted to same accelerated conditions this component only disappears after 150 h of exposure. Non-stabilized and stabilized ABS samples present a similar yellowing behavior, a gradually increase with exposure time. Nevertheless, as expected, color modifications are less pronounced for stabilized ABS samples. The results obtained suggest that a better performance was achieved for stabilized ABS samples with Tinuvin P and Chimassorb 119 FL, which is very important to extend the copolymer lifetime.
Modification of Poly(Ethylene Terephthalate) Track Membrane Properties by Plasma Chemical Method
Authors: Kravets L. , Dmitriev S. , Dinescu G. , Sleptsov V. , Elinson V.
Published: January 2010

Properties of poly(ethylene terephthalate) track membrane (PET TM) exposed to an allyl alcohol radiofrequency plasma after pre-activation its surface in an oxygen plasma were studied. The influence of plasma treatment conditions on basic membrane characteristics, i.e. pore size and shape, wettability, and water permeability, was studied. It has been shown that the plasma treatment of membrane can significantly improve its performance characteristics.
Polymer Composite Nanomembranes with Asymmetry of Conductivity
Authors: Kravets L. , Dmitriev S. , Dinescu G. , Satulu V. , Gilman A. , Yablokov M.
Published: January 2010

This paper describes a structure and electrotransport properties of poly(ethylene terephthalate) track membrane (PET TM) modified by plasma of thiophene. It is shown that the deposition of the polymer on the track membrane surface by plasma polymerization of thiophene in case of forming a semipermeable layer results in creation of composite nanomembrane having in electrolyte solutions of asymmetry of conductivity - a rectification effect. It is caused by presence in the membrane of two layers with various functional groups, and also by changing of the pore geometry. Such type membranes can be used for creation of chemical and biochemical sensors.
Synthesis of Biodegradable Copolymers Based on Ethylene Vinyl Acetate and Polylactic Acid
Authors: Moura Isabel , Machado Ana Vera , Nogueira Regina , Bounor-Legare V.
Published: January 2010

In the present study biodegradable copolymers of ethylene vinyl acetate and polylactic acid were synthesized using transesterification reactions, the structure, morphology, mechanical properties and biodegradability of the produced materials were characterized. Ethylene vinyl acetate was modified with polylactic acid in an internal mixer using titanium propoxide as transesterification catalyst. The graft copolymers were characterized by elemental analysis, infrared spectroscopy, rheology, scanning electron microscopy and thermal analysis. Selective extractions for all copolymers were made, and the results indicate that a maximum of 25 % of EVA-g-PLA copolymer was synthesized by this method. Biodegradation tests were carried out using the standard ISO 14851 (1999), which specifies a method for determining the biochemical oxygen demand in a closed respirometer. This procedure allowed to synthesize biodegradable copolymers with mechanical properties similar to conventional polymers.
Study of Adhesion Relationship of Hydroxyapatite-Titania Coating Obtained by HVOF
Authors: Ferrer Alejandra , Cano Irene G. , Fernández Javier , Guilemany J.M.
Published: January 2010

Hydroxyapatite (HA) coatings are widely used to improve the biocompatibility of titanium substrates. The main problem concerning these coatings is related with the bad adhesion characteristic of the ceramic/metal interface. A TiO2 interlayer can be used to improve the adhesion of the coating; however the TiO2 is a bioinert material. Then, a solution can be the use of a mixture of HA-TiO2 (60% wt HA- 40% wt TiO2) powder has been sprayed by using High Velocity Oxy-Fuel (DJH-2700) for different spraying distances. The adhesion of the coatings has been mechanically tested and the values have been compared with the values obtained for coatings that have been immersed in simulated body fluid solution (SBF) after 24 and 120 hours. The crystallinity degree of the HA plays an important role on it for the dissolution affecting the behaviour of the interface at the same time it is also important osteoclastic resorption and carbonate apatite precipitation.
Degradation and Viscoelastic Properties of PLA-PCL, PGA-PCL, PDO and PGA Fibres
Authors: Vieira A.C. , Vieira J.C. , Guedes R.M. , Marques A.T.
Published: January 2010

Aliphatic polyesters, such as polylactic acid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL), polydioxone (PDO) and others, have been commonly used in biodegradable products. Hydrolytic and/or enzymatic chain cleavage of these materials leads to α-hydroxyacids, which, in most cases, are ultimately assimilated in human body or in a composting environment. However, each of these has some shortcomings, in terms of mechanical properties and degradation time, which restrict its applications. The combination of these materials, by copolymerization or blending, enables a range of mechanical properties and degradation rates. These are extremely promising approaches which can improve or tune the original properties of the polymers. A composite solution of several materials with different degradation rates also enables tuning the rate of degradation of a device and the mechanical properties. After immersion of an aliphatic polyester device, diffusion occurs very rapidly compared to hydrolysis. Therefore, it is usually considered that hydrolysis of ester bonds starts homogeneously and has traditionally been modelled according to a first order kinetics. In this experimental study, fibres of PLA-PCL, PGA-PCL, PDO and PGA, with two different dimensions, were characterized in terms of their degradation rate under three different environments (water, NaCl and PBS) at constant temperature (37°C). Weights and mechanical properties were measured after six different degradation stages. Stages durations were different depending on materials, according to the predicted degradation times. As other thermoplastics, they are viscoelastic materials. In this experimental study mechanical properties of fibres were compared at different strain rates.
Absorption Enhancement of Solar Concentrators via New Surface Photonic Designs
Authors: Lu Ya Lin , Li Ling , Reinhardt Karen A.
Published: January 2010

Enhancing absorption of solar cells over the solar spectrum is one of the most important ways to improve such devices’ performances. In this research, two-dimensional surface photonic designs were suggested to introduce rotationally distributed reciprocal vectors, which will match the guiding modes of the thin planar layer of an active material, and thus to further couple the incident light laterally into the layer. This allows the use of a fewer amount of active materials, increases the devices’ angle acceptance, and reduces costs for both fabrication and system installation.
Advanced Multi-Metallic SOFC Anode Development by Mechanical Alloying Route
Authors: Restivo Thomaz Augusto Guisard , Leite D.W. , de Mello-Castanho Sonia Regina Homem
Published: January 2010

Anodes composed of Ni-YSZ (yttria-stabilised zirconia) cermets are the key material to allow direct biofuel feeding to Solid Oxide Fuel Cell (SOFC) devices due to its internal reforming capability. The main challenge among these materials is related to carbon deposition poisoning effect when C-bearing fuels are feed. The work deals with these issues by alloying Ni with some metals like Cu to conform a multi-metallic anode material. Mechanical alloying (MA) at shaker mills is chosen as the route to incorporate the metal and ceramic powders in the anode material, also leading to better sintering behaviour. A projected cermet material is conceived where a third metal can be added based on two criteria: low Cu solubility and similar formation enthalpy of hydrides regarding Ni. Refractory metals like Nb, W and Mo, seems to fulfil these characteristics, as well as Ag. The MA resulted powder morphology is highly homogeneous showing nanometric interpolated metal lamellae. The sintering behaviour is investigated by conventional dilatometry as well as by stepwise isothermal dilatometry (SID) quasi-isothermal method to determine the sintering kinetic parameters. Based on these tools, it is found the Cu additive promotes sintering to obtain a denser anode and therefore allowing lower process temperatures. The consolidation is achieved through the sintering by activated surface (SAS) method allied to liquid phase sintering process, where the third metal additive also has influenced. The final cermet can be obtained at one sole process step, dispensing pore-forming additives and reduction treatments. The sintered microstructure demonstrates the material is homogeneous and possesses suitable percolation networks and pore structure for SOFC anode applications.
Catalytic Activity of Ni3Al Foils in Methanol Reforming
Authors: Jozwik P. , Grabowski R. , Bojar Z.
Published: January 2010

Intermetallic Ni3Al–based alloys (doped with zirconium and boron) represent a group of advanced materials with potential outstanding physical and chemical properties (such as high catalytic activity and structural stability in corrosive environments) that make them a considerable candidate for many high-tech applications. In this paper, the catalytic activity of fully dense Ni3Al-based thin foils (as thin as 50 m) possessing structures with micrometer or nanometer grain sizes is discussed. The examined material, without any additional catalytic coating, was successfully produced from as-cast coarse-grained sheets by heavy cold rolling and recrystallisation with an appropriately chosen set of parameters. The examination focuses on methanol and methanol/water mixture decomposition into H2 and CO at temperatures up to 530OC in a quartz reactor. Except for these products, a small amount (below 1%) of CO2 and dimethyl ether was observed. The catalyzed reaction began effectively at about 400OC, with a methanol conversion of about 90% or higher.
Effect of Milling Energy Modulation on the High Temperature Synthesis of FeTi
Authors: Livramento Vanessa , Correia Jose Brito , Neves Filipe , Shohoji Nobumitsu , Rangel Carmen M.
Published: January 2010

Depending on the energy level used during mechanical alloying, the constitution of the resulting products can vary extensively. With high energy input, full transformation to the equilibrium phase, FeTi, is achieved. In contrast, for low levels of energy input, the process is akin to mixing without any phase transformation even for extended milling periods. In the present work, nanostructured FeTi powders were produced by mechanical alloying, avoiding the unfavourable agglomeration problem, by using a relatively low level of energy (e.g. 300 rpm) to mill the pure metallic constituents, Fe and Ti, followed by subsequent heat treatment at 800°C. A major achievement of this research was to show that, by modulating the milling intensity and total milling time, the high temperature synthesis reaction of FeTi (1100°C) can be partially or totally suppressed, reverting instead to a metastable reaction path at low temperature (650°C). The mechanical “activation” modifies the reactivity of the system, producing a very thin Ti /Fe layers. That in conjunction with a high level of defects induced mechanically may be responsible for the metastability. Partial substitution of Fe with Ni (10%) resulted essentially in the same phase constitution, indicating solid solution of Ni in FeTi replacing partially Fe lattice positions.
X-Ray Diffraction and Mössbauer Studies of Sigma-FeV Alloys Ball-Milled in Vacuum
Authors: Costa Benilde F.O. , Le Caër Gerard
Published: January 2010

A coarse-grained tetragonal sigma phase Fe47.4V52.6 at% alloy was ground in vacuum in a vibratory mill. The sigma phase transforms into a bcc alpha phase. A concomitant partial amorphisation of the bcc phase occurs. The near-equiatomic FeV alloys are concluded to behave in the same way as the related FeCr alloys when they are ball-milled in vacuum in similar milling conditions. From Mössbauer spectra, it is concluded that about half of the iron atoms are contained in the amorphous phase in the stationary state. From X-ray diffraction patterns there is also a clear evidence of amorphisation, not seen in previously published studies.
Reduction-Carburization of the Oxides of Ni and W towards the Synthesis of Ni-W-C Carbides
Authors: Ahmed H.M. , Miś M. , El-Geassy A.H.A. , Seetharaman Seshadri
Published: January 2010

Ternary Ni-W-C cemented carbides were synthesized directly from mixture powder of NiO-WO3 by simultaneous reduction-carburization in mixed H2-CH4 gas environment in a thin bed reactor in the temperature range 973-1273K. The kinetics of the reaction was closely followed by monitoring the mass change using thermogravimetric method (TGA). The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. The gas mixture ratio was adjusted in such a way that the Ni-W-C formed was close to the two phase tie line. In view of the fact that each particle was in direct contact with the gas mixture, the reaction rate could be conceived as being controlled by the combined reduction-carburization reaction. From the reaction rate, the Arrhenius activation energies were evaluated. Characterization of the carbides produced was carried out by using X-ray diffraction, SEM-EDS as well as high resolution electron microscope (HREM). The grain sizes were also determined. Correlations were found between the carbide composition as well as grain size and the process parameters such as temperature of the reduction-carburization reaction as well as the composition of the gas mixture. The results are discussed in the light of the kinetics of the reduction of oxides and the thermodynamic constraints.
Surface Structure of NiTi Alloy Passivated by Autoclaving
Authors: Morawiec Henryk , Goryczka Tomasz , Lelątko Józef , Lekston Zdzisław , Winiarski Antoni , Rówiński Edward , Stergioudis F.
Published: January 2010

Sterilization of the NiTi alloy in boiling water or steam causes passivation, which results in an amorphous 3.5 nm thick TiO2 layer on the surface. Between the surface and the matrix a transition layer of Ni2O3 and NiO was observed, using the X-ray photoelectron spectroscopy. Differences in sterilization conditions affect the amount of metallic nickel on the surface.
Hydrogen Brittleness of Austenitic Steels
Authors: Gavriljuk Valentin , Shyvanyuk Vladyslav N. , Teus S. M.
Published: January 2010

The electronic concept for hydrogen embrittlement (HE) of austenitic steels is developed based on the hydrogen-caused increase of the concentration of free (i.e. conduction) electrons. It is shown that, as consequence, the shear module locally decreases, which in turn leads to the decrease in the stress for activation of dislocation sources, the line tension of dislocations, the distance between the dislocations in pileups and, in consistency with the theory of hydrogen-enhanced localized plasticity (HELP), promotes the reversible hydrogen brittleness. The analysis of the electronic and elasticity approaches to HELP is carried out using the experimental data. The effect of alloying elements on the mechanical properties is studied and a concept for design of hydrogen-resistant austenitic steels is proposed.
Physical Characterization of Plasma Deposited Polymeric Proton Exchange Membrane Used in Fuel Cells
Authors: Polak Peter Lubomir , Mansano Ronaldo Domingues , Silva Rui Alberto , Silva Igor Proença , Ribeiro Maria Cristina
Published: January 2010

The performance of fuel cells is largely dependent on the properties of the membrane electrode assembly (MEA) which consists of a polymer electrolyte membrane and carbon based electrodes. The aim of this work was to obtain new polymer membranes and carbon thin films (for comparison) by Plasma Enhanced Chemical Vapor Deposition (PECVD) and proceed to their physical characterization in order to be able to choose the best conditions that may lead to outstanding proton exchange membranes. The films were deposited on silicon wafers and were analyzed by Scanning Electron Microscopy and Energy Dispersive Spectroscopy (SEM/EDS), Electron Spectroscopy for Chemical Analysis and X-Ray Photoelectron Spectroscopy (ESCA-XPS), Atomic Force Microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and Rutherford Backscattering Spectrometry (RBS). SEM/EDS and XPS analysis have shown that the chemical composition of the films varied as a function of the plasma (relative percentages of the reactant gases CH4 and SF6) while variation of the pressure and RF power did not have a marked effect on the topographic quality and composition of the membranes. AFM analysis, as well as SEM, made possible to observe the topography of the membranes showing that the films are very smooth with some localized defects. Futhermore, AFM micrographs have shown that the roughness (root mean square - RMS) of the membranes have peak to valley differences in the order of some nanometers. RBS and Profilometer techniques indicated that the deposition rate of the films is not linearly dependent on the plasma composition while FTIR spectroscopy has shown the presence of the perfluorinated sulphonate groups.
Production of Glucose by Starch and Cellulose Acid Hydrolysis and its Use as a Fuel in Low-Temperature Direct-Mode Fuel Cells
Authors: Spets Jukka Pekka , Kuosa Maunu , Granström Tom , Kiros Yohannes , Rantanen Jyri , Lampinen Markku J. , Saari Kari
Published: January 2010

The use of glucose, which is produced from the acid hydrolysis of starch and cellulose, is studied as a fuel in a low-temperature direct-mode fuel cell (LTDMFC) with an alkaline electrolyte. Glucose is regarded as being as good a fuel as bioethanol, because both the fuels give 2 electrons per molecule in the fuel cell without carbonisation problems. However, glucose can be produced with fewer processing stages from starch and cellulose than can bioethanol. In the LTDMFC the fuel and the electrolyte are mixed with each other and the fuel cell is equipped only with metal catalysts. Cellulose as a fuel is of great importance because the fuel for the energy production is not taken from food production. A description of an acid hydrolysis method for starch and cellulose is presented. Values for glucose concentrations in each hydrolysate are analysed by means of a chromatographic method. Each glucose hydrolysate was made alkaline by adding of potassium hydroxide before feed in the fuel cell. Polarisation curves were measured, and they were found to produce lower current density values when compared to earlier tests with pure glucose. The Coulombic efficiency of pure glucose electrochemical oxidation in LTDMFC, which was calculated from a ratio of detected current capacity (As) to the maximum current capacity with the release of two electrons per molecule, was also found to be very low. Concerning the hydrolysates, the glucose concentrations were found to have values that were too low when compared to the earlier tests with pure glucose in a concentration of 1 M. The further development demands for the system under consideration are indicated. The concentration of glucose in the hydrolysate is essential to achieve high enough current density values in the LTDMFC.
Qualification of an Investment Casting Process for Production of Titanium Aluminide Components for Aerospace and Automotive Applications
Authors: Aguilar Julio , Hecht Ulrike , Schievenbusch Andre
Published: January 2010

Over the past years significant efforts were dedicated to developing production processes for aerospace and automotive parts from light weight titanium aluminides. Considerable progress was achieved worldwide in the field of near net shape casting. Access has developed an own production route, based on centrifugal investment casting. Various components from TiAl-based alloys, including turbocharger wheels and stator vanes were successfully cast and supplied for engine tests. A newly developed automated centrifugal casting line was recently taken into operation. This presentation will describe our activities that aimed to qualify the casting line for series production of turbocharger wheels: apart from basic issues of casting cluster design, process control and quality inspection we will discuss the casting process from the perspective of its techno-economic characteristics
The Effect of Impact on the TiAl Alloy TNBV3B Produced on Three Different Processing Routes
Authors: Gebhard Susanne , Peters Piet , Roth-Fagaraseanu Dan , Turley Felix , Voggenreiter Heinz
Published: January 2010

The impact behaviour of the TiAl alloy TNBV3B produced on three different processing routes - cast, forged (with a relatively small degree of deformation) and extruded - has been studied making use of ballistic tests. The damage evolution due to centre and edge impacts on flat and airfoil-like specimens has been investigated with a focus on the influence of the microstructure. Apart from the influence of material properties, the impact location showed a strong effect on the damage evolution. The extension of impact cracks in the interior of the specimens has been studied making use of heat tinting experiments and computer tomography analyses.
Microstrain Analysis of Titanium Aluminides
Authors: Héripré E. , Caldemaison D. , Roos A. , Crépin J.
Published: January 2010

The aeronautic and automotive industries have shown a renewed interest in TiAl based
alloys. The main reasons for such an interest are their low density (~3,8g/cm3), a good stiffness and
a high strength for temperatures up to 750°C. However, these alloys exhibit, in their polycrystalline
form, a poor ductility at room temperature with widely scattered values. The aim of this study is
therefore to characterise their mechanical behaviour with a multiscale methodology, coupling
microstructure analysis and strain field measurements. This methodology employs orientation
imaging microscopy as well as digital imaging correlation techniques with an intragranular step size
of a few micrometers.
Two chemical compositions (47 at. % Al and 48 at. % Al) and two processing routes (casting and
powder metallurgy) are studied. Thus, four different types of final microstructures are considered,
from fully lamellar Ti3Al (a2) + TiAl (g) microstructure to bimodal ones composed of two-phase
(a2+g) lamellar grains and monolithic g grains. Firstly, the microstructure is characterised
crystallographically and morphologically. This allows the identification of a representative volume
element (RVE) inside the analysed volume. Then, uniaxial mechanical tests are performed for each
microstructure, and the strain fields are analysed with a multiscale approach, which determines the
spatial distribution of the strain field heterogeneity with respect to the different microstructures.
Microstructure and Mechanical Properties of a Cast Intermetallic Ti-46Al-8Ta Alloy
Authors: Lapin Juraj , Gabalcová Zuzana , Pelachová Tatiana , Bajana Oto
Published: January 2010

Microstructure and mechanical properties of a new cast air-hardenable intermetallic Ti-46Al-8Ta (at.%) alloy are studied. Primary solidification phase, solidification path and high temperature phase equilibria are determined using quenching during directional solidification (QDS) experiments combined with microstructural analysis. Vickers hardness, tensile, compression and creep properties are presented. The effect of short-term high temperature exposure on room temperature (RT) ductility of uncoated specimens is evaluated and discussed. Creep properties such as minimum creep rate, time to 1 % creep deformation, fracture time and creep fracture mechanisms are presented and compared to other TiAl base alloys developed for industrial applications. Long-term high temperature microstructural stability and the effect of ageing on Vickers hardness and RT tensile properties are presented. Based on the achieved experimental results, the potential of this new alloy to fulfill industrial specifications is discussed.
Non-Destructive Fluorine Depth Profiling as Quality Assurance for the Oxidation Protection of TiAl Turbine Blades
Authors: Neve Sven , Stiebing Kurt , Schmidt Lothar P.H. , Zschau Hans Eberhard , Masset Patrick J. , Schütze Michael
Published: January 2010

Using the halogen effect TiAl-alloys can be protected against high-temperature oxidation. Two different fluorination methods were applied to turbine blades. The mass increase due to oxidation can be drastically reduced compared to untreated specimen. A new vacuum chamber for ion beam analysis was developed to analyze the real parts. Using PIGE-technique the F-content as a function of depth before and after oxidation was detected. Thickness and composition of the oxide scale were measured by RBS. Both ion beam methods were non destructive and thus enabled for the first time quality assurance of the halogen treatment on real components.
Fe-6.5wt.%Si High Silicon Steel Sheets Produced by Cold Rolling
Authors: Ye Feng , Liang Y.F. , Wang Y.L. , Lin Jun Pin , Chen G.L.
Published: January 2010

High silicon steel with Si content of 6.5wt.% is perspective to be applied in magnetic devices at high frequencies. It is very hard to produce Fe-6.5wt%Si alloy thin sheet by conventional hot-cold rolling method because of its embrittlement at room temperature resulted from the formation of intermetallic phases like B2 and D03. In this paper, embrittlement mechanism, rolling processes, and magnetic properties for the cold rolled Fe-6.5wt.% Si alloy sheets are discussed. Our study indicates that thermal mechanical treatments can improve the ductility of the Fe-6.5wt.%Si alloy. The Fe-6.5wt.%Si alloy sheets of 0.05 mm thickness can be successfully obtained after hot-cold rolling and heat treatments. Lamination pieces can be punched directly from the sheets. Tensile strength as high as 1048MPa and elongation over 3% were measured at room temperature.
Effect of Annealing on Microstructure and Mechanical Properties in Mg-Zn-Y Alloy with Long Period Stacking Order Phase
Authors: Noda Masafumi , Kawamura Yoshihito
Published: January 2010

Lightweight Mg alloys are being widely adopted in electronic devices and automotive parts. However, the mechanical properties of Mg alloys are inferior to those of Al alloys, and their range of applications is limited. Recently, Mg-Zn-Y alloys have been found to exhibit superior mechanical properties to other Mg alloys. However, for use as industrial materials, it is necessary to improve their ductility while retaining their strength. We studied the mechanical properties of extruded Mg96Zn2Y2 alloy with long-period stacking order (LPSO) phases, in addition to the thermal stability of its structure during annealing. The elongation of the alloy improved from 5 % to 10 % with slightly loss of strength up to an annealing temperature of 623 K. Even at this temperature, it was possible to maintain good mechanical properties and a thermally stable microstructure.
Influences of Rolling Conditions on Texture and Formability of Magnesium Alloy Sheets
Authors: Huang Xin Sheng , Suzuki Kazutaka , Watazu Akira , Shigematsu Ichinori , Saito Naobumi
Published: January 2010

The AZ61 magnesium alloy was subjected to the differential speed rolling at different rolling conditions including reduction per pass, rotation speed ratio and rolling temperature, and the influences of the rolling conditions on microstructure, texture, mechanical properties and formability of the as-rolled sheets were investigated. Increasing the reduction per pass results in a more homogeneous microstructure and a relatively weaker basal texture. With increasing the rotation speed ratio, the inclination angle of basal pole toward the rolling direction increases and the stretch formability enhances correspondingly. Increasing the rolling temperature has an effect on weakening the basal texture intensity and leads to the enhancement of stretch formability.
Problems and Promises of Metal Matrix Composites
Authors: Taillard Roland
Published: January 2010

The field of application of composites is ever-growing because of their unrivalled combinations of functional and structural properties. Such associations seem the more improvable as there are at once manifold possibilities to modify the architecture of composites, their route of elaboration, an ever-increasing scientific potency for both experimental investigations and modelling, and always more demanding materials performances in projects.
This presentation wants to illustrate all these aspects by the example of metal matrix composites (MMCs) mostly elaborated by severe plastic deformation. Emphasis is given to results dealing with the effects of composite design and conditions of metalworking on the success of the fabrication process that depends on the uniformity of deformation and/or on the quality of the interfaces. At last, the consequences of all these data, and the need of complementary work, for the continuous improvement of the properties MMCs are delineated.