bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis, Magnetic and Mössbauer Studies of Mechanically Alloyed Fe0.63Si0.37 Alloys
Authors: Costa Benilde F.O. , Amaral Vitor S. , Le Caër Gerard , Le Caër Gerard
Published: March 2009

Elemental powder mixtures of Fe and Si were mechanically alloyed with a ball-mill.
Mössbauer spectroscopy and X-ray diffraction were used to characterise the microstructural
changes of these mixtures which are induced by high-energy ball-milling. Mössbauer spectra are
discussed in terms of two main spectral components (corresponding to FeSi alloy and α-Fe) and the
time dependence of the alloy formation follows a Johnson-Mehl type law. Calorimetry
measurements show that the formed alloy is stable up to 800°C as no crystallisation or phase
transformation peaks are observed. From X-ray diffraction, a crystallite size of 9 nm is obtained.
Magnetic measurements at low temperature were carried out on the final alloy and the saturation
magnetic moment at 4.2K is 0.44 μB/Fe.
Development and Interfacial Properties of Novel Polymer-Modified Carbon Film Electrodes
Authors: Gouveia-Caridade Carla , Brett Christopher M.A. , Liess Hans Dieter
Published: March 2009

The surface properties of carbon film electrode sensors covered by coating with Nafion
polymer film, before and after electrochemical analysis of sub-micromolar traces of lead and
cadmium ions, were investigated. These protective polymer films are applied to the electrode
surfaces to prevent the irreversible adsorption of chemical species, such as proteins and surfactants
present in natural media, which leads to a decrease in response. Electrochemical impedance
spectroscopy and voltammetric techniques were used for characterisation. The effect of non-ionic
surfactant molecules in solution on the behaviour of the polymer-coated electrode was also
investigated. It is shown that permanent changes to the structure and morphology of the Nafion film
and of the carbon-Nafion interface occur after deposition of the trace metal ions, an effect which is
lessened in the presence of surfactant.
EPR and TEM Characterization of Electroluminescent Alq3
Authors: Grecu Maria Nicoleta , Ghica Cornel , Mirea Anisoara , Grecu Voicu V. , Schwoerer Markus
Published: March 2009

EPR and TEM investigations on sublimated solid Alq3, [tris(8- hydroxyquinoline)aluminum(III)] are reported. Different paramagnetic centers in microcrystalline
Alq3 fractions as synthesized and annealed are observed. Their nature, thermal treatment dependence, as well as correlation with the crystal structure are analyzed. The existence of randomly oriented triplets and quartets in annealed Alq3 fractions is evidenced from the temperature dependence of X- and Q-band EPR spectra. The spin Hamiltonian parameters are given and proposals for the model structures are made.
Simulations of Cyclic Plasticity and Fatigue Behavior of Structural Steels under Multiaxial Loading
Authors: Li Bin , Reis Luís G. , de Freitas Manuel
Published: March 2009

The local cyclic elastic-plastic stress-strain responses were simulated using the
incremental plasticity procedures of ABAQUS finite element code. It is shown a better
understanding on the evolutions of the local cyclic stress-strain and the strong interactions between
the most stressed material element and its neighboring material elements in the plastic deformations
and stress redistributions. Based on the stress/strain states of the stabilized cycle, a new damage
parameter, proposed on modification of the ASME code parameter, is applied and improved
correlations between the predicted and the experimental fatigue lives are shown. It is concluded that
the improvement of fatigue life prediction depends not only on the fatigue damage models, but also
on the accurate evaluations of the cyclic elasto-plastic stress/strain responses.
Modelling Local Brittle Zones in Welds Using the Finite Element Method
Authors: Teixeira Pedro , Rodrigues Dulce Maria Esteves , Loureiro Altino
Published: March 2009

This paper reports the results of a numerical study concerning the influence of local
brittle zones intersecting the crack front on the fracture behaviour of welded joints. This work was
performed using the numerical simulation of the three point bending test of weld samples with
different amount of brittle structures at the crack front. Using 3D finite element discretization it was
possible to simulate welded samples with very small fractions of brittle zone at the crack front, such
as 5 %. Comparing the results of samples with increasing proportion of brittle zone it was observed
a significant decrease in the crack growth resistance with increasing amounts of brittle material.
This decrease in crack growth resistance was obtained even for samples with very small amounts of
brittle material at the crack front.
Improving Profile Cooling through Modeling
Authors: Nóbrega João M. , Carneiro Olga S.
Published: March 2009

A 3D numerical code, based on the finite volume method, able to model the cooling stage
of an extrusion line is presented and validated. For this purpose, an analytical solution of a simple
heat transfer multi domain problem was developed, the result obtained being compared with the
predictions given by the numerical code. A prior study performed with the above mentioned code
showed that in general when a reduction of the profile average temperature is imparted, lower
temperature homogeneity is also obtained, being the only exceptions the reduction of the extrusion
velocity and splitting the calibrator into several units, separated by annealing zones. Therefore, the
only way to improve the cooling efficiency without compromising the production rate is to divide
the total cooling length into several independent units. In this work that investigation is further
extended to study the influence of the individual cooling units and annealing zones lengths
distributions on the global cooling efficiency.
Modeling and Computation of Hydroxyapatite Nanostructures and Properties
Authors: Bystrov Vladimir , Bystrova Natalia , Paramonova Ekatherina , Sapronova A. , Filippov S.
Published: March 2009

Hydroxyapatite (Ca5(PO4)3 OH) (HAp) is a crystalline structure and composition
analogue to calcified tissues of vertebrates. The biomedical significance of HAp is its bioactivity –
HAp ceramics leads to the formation of new bone on their surface. HAp properties are ascribed to
the characteristic surface structure of HAp, while the detailed mechanism is still unknown.
Modeling and computation of HAp molecular nanostructures, exploration of the possible
mechanisms of its surface charging (polarization), based on proton transfer, and the discussion of
the adhesion properties of HAp nanoparticles and ceramics are the aim of the work.
Influence of the Weld on the Mechanical Behaviour of Tailor Welded Blanks
Authors: Baptista António José , Rodrigues Dulce Maria Esteves , Menezes Luis Filipe
Published: March 2009

In new car production, an innovative method to produce strong and light panels consists
in applying Tailor Welded Blanks (TWBs) in the body-in-white base structure. Since the fusion
welding processes can induce significant changes in the material properties of the base materials, an
important question is whether the weld bead has a significant influence on the overall behaviour of
the welded blanks. In this work, some preliminary conclusions on this subject were achieved based
on results of the numerical simulation of simple mechanical tests: tensile, shear and simple bending.
The numerical simulations were performed with a fully implicit finite element program (DD3IMP).
The results obtained show that for a slight mismatch of properties between the weld and the base
materials, no important influence of the weld in the TWBs behaviour is noticed. However, a
significant strength reduction can be observed for strong undermatch conditions (lower mechanical
properties in the weld) even when the weld bead is very narrow.
Sintering M3/2 High Speed Steel Powder by DMLS Process
Authors: Martins Isabel M. , Esperto Luis , Santos Mário J.G.
Published: March 2009

The Direct Metal Laser Sintering (DMLS) technology uses a mixture of metal powders with different melting points to build objects layer by layer, directly from the geometric digitalised information. This process allows the manufacturing of prototype and production tools.
In this study, the M3/2 high speed steel powder blended with 20 wt.% Cu3P and 0.25 wt.% graphite was laser-sintered, using two scan speeds (100 and 200 mm/s), keeping constant both hatching (0.30mm between two consecutive lines) and laser power (180W). The powder was spread in uniform layers of about 20m over a steel plate (100x60x6mm). The laser beam scanned small areas (12x15mm) in a single direction (OX). The surface morphology of the laser-sintered material shows that all material melted, but for 200mm/s scan speed, strings are well defined. This is probably due to a lower level of energy supplied to the material. The microstructure of the sintered material was studied in the longitudinal and transverse sections, to evaluate the consolidation process and layer growth. The material showed porosity and cracks formed during the process.
Metallurgical Study of a AISI 316L Stainless Steel Used in a Gas Turbine Exhaust System
Authors: Martins Rui F. , Branco Carlos M. , Gonçalves-Coelho António M. , Gomes Edgar C.
Published: March 2009

Several high temperature fatigue and possibly creep-fatigue cracks have nucleated and
propagated through the 3.7 mm wall thickness of a gas turbine exhaust system of a navy combat
ship made of a grade type AISI 316L annealed stainless steel. The main cracks propagated near
some welded joints, where the measured working temperature was approximately equal to 350°C
(Fig.1). The paper presents tensile, fatigue and creep data obtained from experimental tests that
were performed in several test specimens obtained from steel plates used in-service. Results of
optical microscopy for the microstructure of the material and analysis of the fracture surfaces
carried out with the SEM have identified the failure mechanisms at test temperatures. The paper
also presents microhardness and grain size measurements carried out together with microstructural
observations in the SEM. A research work to investigate carbide precipitation in virgin thin sheet
specimens, as used in these exhaust tubes, was also performed and it is presented. The influence of
stages time (100, 200, 100+100 and 4x50 hours) and of thermal exposure temperatures (500 and
550°C) was assessed to compare the metallurgical properties of the material. Finally, the paper
shortly analyses other materials that could replace the used one.
Optimised Conditions for the Obtaining of Metakaolin
Authors: Teixeira-Pinto Amândio , Vieira Eduardo
Published: March 2009

Aluminosilicates represent the major group of solid inorganic matter of the terrestrial
crust. In specific conditions of temperature and pressure, the aluminosilicates may, in strong
alkaline environment, react among themselves, giving place to the formation of stable materials of
high mechanical strength, able to support high levels of temperature and resistant to acid action.
They also have the ability for the immobilisation of heavy metals and radionuclides.
When subject to a previous thermal treatment, certain aluminosilicates like kaolin, can be directly
activated at room temperature and normal pressure.
In this work, the conditions of preparation of metakaolin (a meta-phase of kaolin) are optimised.
Temperatures of kaolin dehydration and exposition time to temperature are studied by the use of
XRD, FTIR and NMR-MAS, and so far by the application of Murat-Bachiorrini Criterion. The
results obtained show that energy savings are considerable.
Technical Features Evaluation of an Alumina Powder Prepared by Combustion Synthesis
Authors: Tavares A. Patrícia , Olhero Susana M.H. , Ferreira José Maria F.
Published: March 2009

This work aims at characterising an alumina powder obtained by combustion synthesis,
and at evaluating the technical properties of sintered bodies. Particle size distribution and XRD
were used to characterise the alumina powder; electrophoresis and rheological measurements were
used to select the most suitable processing conditions. Sintered density, flexural strength, Vickers
hardness and SEM analysis were used to characterise the bodies sintered at 1600°C. The
experimental results showed that a density of 3.60 g/cm3 could be obtained in absence of sintering
aids and that the sintered bodies exhibited a flexural strength of 220 MPa and a Vickers hardness of
1100.
In Situ Observation of Ni-Ti Thin Film Growth by Synchrotron Radiation Scattering
Authors: Martins Rui Miguel S. , Braz Fernandes Francisco Manuel , Silva Rui Jorge C. , Beckers Manfred , Schell Norbert
Published: March 2009

A sputter deposition chamber inserted into the six-circle Huber diffractometer of the
materials research station of the ROssendorf BeamLine (ROBL-CRG) at ESRF allowed to perform
in-situ experiments during film growth of Ni-Ti. It is equipped with Kapton windows for X-Ray
Diffraction (XRD) and specular Reflectivity (XRR) measurements. By following in situ the
evolution of the structure of the growing film, we reveal intermediate “states” which cannot be
seen/revealed ex situ, because those states occurred only during the growth but were no longer
visible after deposition. Vertical Bragg-Brentano large-angle scattering geometry was employed to
study the different trends of structural transformations taking place during deposition. Ni-Ti films
exhibiting a non-uniform phase content across the film thickness could be produced by varying the
power of co-sputtering Ni-Ti plus Ti. A significant decrease of IB2{110}/IB2{200} was observed when a
bias of -45 V was applied.
Influence of Surface Roughness on the Quality of Data Obtained by Pseudo-Grazing Incidence X-Ray Diffraction
Authors: Marques Maria José , Pina J.C.P. , Dias A. Morão
Published: March 2009

The conventional Bragg diffraction geometry, normally used to characterize the residual
surface stress state, it is not suitable to evaluate surface treated materials and thin films. The X-ray
path lengths through a surface layer or thin film are too short to produce adequate diffraction
intensities in relation to the bulk or the substrate. Another limitation of the conventional technique
appears when a residual stress gradient is present in the irradiated surface. The technique only
enables the evaluation of the mean value of this gradient. In these cases, a recently proposed
Pseudo-Grazing Incident X-ray Diffraction method would be better applicable.
In this study, the Pseudo-Grazing Incidence X-ray Diffraction is applied to characterize the residual
stress depth profiles of several AISI 4140 samples, which were prepared, by mechanical polishing
and grinding, in order to present different surface roughness parameters, Ra. The experimental
results lead to the conclusion that the surface roughness limits the application of the
Pseudo-Grazing Incidence methodology to a minimum X-ray incident angle. This angle is the one
that enables a mean X-ray penetration depth with the same order of magnitude of the sample surface
roughness parameter, Ra.
Provenance Characterization of Archaeological Ceramics by Laser Induced Plasma Spectroscopy
Authors: López Ana J. , Ramil Alberto , Nicolas Gines , Mateo Mari Paz , Piñon Victor , Yáñez Armando
Published: March 2009

Archaeological ceramics Terra Sigillata manufactured in different production centres
have been studied by “laser induced plasma spectroscopy” (LIPS). The aim of this work is to
demonstrate the capability of LIPS for the classification of pottery shreds in function of their
provenance. Characteristic emission spectra of different pottery groups were obtained and simple
linear correlation methods were used for grouping samples. In addition, complementary scanning
electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM-EDX) analysis were
performed to obtain morphological features and to confirm chemical results
Effect of Dolomite Addition on the Densification of Fly Ash Based Ceramics
Authors: Monteiro Regina da Conceição Corredeira , Mota C.S. , Lima M.M.R.A.
Published: March 2009

Fly ash from Tapada do Outeiro, a coal power plant in the north of Portugal, has been
processed by a powder technology route in order to obtain durable and mechanical resistant
ceramics. Dolomite (CaCO3.MgCO3) was added in different proportions to the waste material,
from zero up to 10 wt%, and the effect of this addition on the densification behaviour of the fired
samples was investigated by measuring the apparent density, the open porosity and the linear
shrinkage. The powder mixtures were uniaxially dry pressed in a steel die and fired at temperatures
ranging from 950 to 1150°C. XRD and SEM were used to identify the phases present in the sintered
materials and the degree of densification. The results revealed that added dolomite was responsible
for the appearance of anorthite, an extra phase besides mullite and quartz, for an increase in the
amount of liquid phase and for the swelling of closed pores at the highest firing temperatures.
Significant morphological changes and phase transformations occurred during sintering and their
effects on the physical-mechanical and leaching characteristics of the sintered materials were
analyzed.
Growth of Lead Zirconate Titanate Single Crystals by the High Temperature Solution Method
Authors: Pérez de la Torre José A. , Soares Maria do Rosário , Mantas Pedro Q. , Amorín Harvey , Costa Maria Elisabete V. , Senos Ana Maria R.
Published: March 2009

To grow single crystals within the solid solutions between PbZrO3 and PbTiO3, PbZrxTi1- xO3 or PZT, is very difficult when compositions are around the morphotropic phase boundary (MPB). In this work, the PZT single crystals were grown by the high temperature solution method, using fluxes with a constant composition, different thermal profiles and different flux/PZT ratios.
This approach was successful used to obtain PZT single crystals with compositions near the MPB, of 2 × 2 × 2 mm3 size and without second phases. The specific experimental conditions to obtain these crystals are analysed and discussed.
Piezoelectric Material for High Efficiency Ultrasonic Siren
Authors: Dimitriu Elena , Iuga Alin
Published: March 2009

A PZT-type material, doped with niobium and lithium was prepared by the ceramic
technique. The microstructure of the sintered material at 1280oC was performed by scanning electron microscopy (SEM), transmission electron microscopy and by X-ray diffraction. Dielectric and piezoelectric properties were measured. The good planar properties of the material made it possible to obtain ceramic disks with a strong radial mode. Two such disks, glued together, with opposed polarisation constitute a bimorf element, which successfully converts the radial mode into
a flexural one. At the center of the bimorf a conical acoustical impedance adapter is fixed in order to increase the frontal acoustical emission of the device. This ultrasonic device provides a broad – band, high acoustical emission, and is suitable to work as a high efficiency ultrasonic siren. It can be used in intruder alarm devices, ultrasonic telemeters.
The Influence of DC Bias on the Dielectric Response of Sr1-xCaxTiO3 Ceramics
Authors: Tkach Alexander , Araújo Branca , Vilarinho Paula M.
Published: March 2009

The effect of the electric field on the dielectric response of the Sr1-xCaxTiO3 ceramic system was analysed and complemented by structural and microstructural studies. A monotonic decrease of the lattice parameter and an increase of the average grain size from 11 to 23 μm with increasing x were observed by X-ray diffraction and scanning electron microscopy analysis respectively. Samples with x = 0.003 and 0.01 reveal a monotonous increase of low-temperature dielectric constant, corresponding to an enhancement of the tunability and a reduction of the driving electric field at 10-30 K for x = 0.01. For Sr1-xCaxTiO3 ceramic samples with x = 0.04 and 0.10 the ferroelectric phase transition of around 20 K was observed together with the enhanced tunability of the dielectric constant at 30-85 K for x = 0.10.
Transport Properties and Thermal Expansion of SrCe(Y)O3-δ Ceramics
Authors: Marozau Ivan P. , Kharton Vladislav V. , Frade Jorge R. , Marques Fernando M.B.
Published: March 2009

Oxygen transport properties of perovskite-type SrCe1-xYxO3-δ (x = 0.05–0.10), exhibiting protonic transport in hydrogen-containing reducing atmospheres and mixed oxygen-ionic and ptype electronic conductivity at oxygen partial pressures close to atmospheric, were studied at 973– 1223 K under oxidizing conditions. The oxygen transference numbers of SrCe(Y)O3-δ in air vary in
the range 0.37–0.80, decreasing when temperature increases. The oxygen permeability is significantly affected by the hole conduction, which influences both bulk ambipolar conductivity and surface exchange kinetics. The average thermal expansion coefficients of SrCe1-xYxO3-δ ceramics, calculated from dilatometric data in air, are (11.1–11.3)×10-6 K-1 at 373–1373 K.
Conductivity of La- and Pr- Doped Bi4V2O11
Authors: Paściak Grzegorz , Chmielowiec Jacek , Bujlo Piotr
Published: March 2009

Presented work concerns BIVOX based solid electrolytes doped with lanthanum and
praseodymium. Investigations of melting point and composition of new materials were performed by use of DTA and X-ray measurements. For determination of conductivity the impedance spectroscopy (IS) method was applied. Measurements were performed in wide range of frequency 20 Hz – 1 MHz and temperature 150 – 750 oC. The electrical measurements allowed evaluation of
possible application in SOFC.
Mixed Conductivity of Ce- and Nb-Substituted (La, Sr)FeO3-δ
Authors: Kharton Vladislav V. , Viskup A.P. , Kovalevsky Andréy V. , Shaula A.L. , Frade Jorge R. , Marques Fernando M.B.
Published: March 2009

Due to relatively high oxygen permeability, lanthanum-strontium ferrite phases are of
interest as ceramic membrane materials for the partial oxidation of natural gas. This work was focused on the study of perovskite-type ferrites co-doped with Sr2+ and Ce4+ or Nb5+, with particular emphasis on the ionic transport and thermodynamic stability limits at low oxygen chemical potentials. Dense membranes of La0.5-2xCexSr0.5+xFeO3-δ (x = 0 - 0.2) and La0.5-2ySr0.5+2yFe1-yNbyO3-δ
(y = 0 - 0.1) were characterized employing X-ray diffraction (XRD), scanning electron microscopy (SEM), dilatometry, oxygen permeation and faradaic efficiency studies, and the measurements of total conductivity and Seebeck coefficient in the oxygen partial pressure range from 10-20 to 0.5 atm. The incorporation of Ce4+ or Nb5+ was found to decrease thermal expansion and electronic transport parameters, whereas the ionic conductivity behavior is complex, indicating the relevance of redox interactions of the variable-valence cations and the concentration of mobile oxygen vacancies.
Importance of Textural Characteristics in the Adsorption of Hydrogen onto Activated Carbon and Activated Carbon Fibers
Authors: Salvador-Palacios Francisco , Sánchez-Montero M.Jesus , Sangüesa-Domínguez Isidro , Izquierdo-Misiego Carmen
Published: March 2009

This paper highlights the importance of micropore size of carbonous materials in the
storage capacity of hydrogen. A study is made of a series of carbon fibers with different burn off, activated by a new procedure in which supercritical CO2 is used, as well as of several activated carbons. The best storage results at 77 K and 1 bar corresponded to the activated carbon fibers. The maximum value obtained for these materials was 2.86wt%, significantly higher than that obtained previously by other authors. The study shows that storage increases rapidly with the degree of
activation of the fiber and is closely linked to the micropores. Micropores of around 0.6 nm are those responsible for the greater increase in storage. This study confirms that activation with supercritical CO2 may lead to microporous solids with enormous capacity for adsorbing H2.
Effect of Oxidant/ Monomer Ratio on the Electrical Properties of Polypyrrole in Tantalum Capacitors
Authors: Gonçalves Gonçalo , Fortunato Elvira , Martins J.I. , Martins Rodrigo
Published: March 2009

In this work, the relation between oxidant/monomer ratio and the electrical conductivity of polypyrrole was studied using different ratios. We achieved a maximum value for electrical conductivity of 7.5 S/cm for a ratio of 2:1. We also developed a chemical dip-coating process to produce the cathode layer in tantalum capacitors. We obtained capacitances of about 80 µF after 8 cycles using the sequence Monomer/Oxidant.
Structure and Electrochemical Characterization of Electrolytic Ni-Co-P and Ni-W-P Layers
Authors: Popczyk Magdalena , Budniok Antoni , Scholl Henryk , Blaszczyk Tadeusz
Published: March 2009

Ni-P, Ni-Co-P and Ni-W-P layers were obtained in galvanostatic conditions, at the
current density jdep= 0.200 A cm-2. The X-ray diffraction method was used to determine phase composition of the layers and the atomic absorption spectrometry was applied to specify their chemical composition. A metallographic, stereoscopic and tunneling microscope and also Form Talysurf-type profilograph were used for cross-section and surface morphology characterization of the layers. The behaviour of obtained layers was investigated in the processes of hydrogen and oxygen evolution from 5 M KOH using voltammetry method. It was ascertained that, introduction of cobalt or tungsten into Ni-P matrix, lead to obtain the layers about very developed surface. Thus obtained layers may be useful in application as electrode materials in electrochemistry.
Effect of Aluminising on the Hot Corrosion Resistance of Nickel-Chromium Alloys
Authors: Sequeira César A.C. , Marquis Fernand D.S.
Published: March 2009

The effects of aluminising on the hot corrosion resistance of two nickel-chromium alloys containing 10 and 30 weight percent chromium, respectively, were examined. The Ni/Cr specimens were aluminised by pack cementation in Ar and underwent cyclic hot corrosion testing in Na2SO4- NaCl molten salt. XRD analysis indicated that a NiAl phase formed between the coating layer and substrate. Cyclic hot corrosion test results indicated that the effects of aluminising are more
pronounced in the case of the 10 % Cr than in the case of 30 % Cr. The ductile NiAl phase suppressed the potential for crack initiation during thermal cycling of the 10 % Cr specimens, and reinforced the hot cyclic corrosion resistance in molten salt for the 30 % Cr specimens.
Effect of Vanadium and Carbon Content on the Sinterability of Water Atomised High Speed Steel Powders
Authors: Mascarenhas João M.G. , Oliveira Manuela , Wright C. Steven
Published: March 2009

This paper presents the results of an investigation into the sintering behaviour of three vanadium enriched variants of T42 high-speed steel. Powders were prepared by water atomization with vanadium and carbon contents of 6-8 wt% and 2.2 -2.7 wt%, respectively. These were annealed, die pressed and sintered in vacuum. All three alloys were sintered to full density giving “as –sintered” microstructures comprising globular MC carbides dispersed in a martensitic matrix. Optimum sintering temperatures were in the range 1240 - 1250°C with lower optimum temperatures associated with higher carbon levels. Sintering characteristics are correlated with phase diagrams calculated using ThermoCalc™ software and TCFe2000 database. The implications for the design of sinterable vanadium containing high-speed steels are discussed.
Study of Abrasion Resistance of Steels by Micro-Scale Tests
Authors: Braga D. , Ramalho Amilcar , Silva Pedro Nuno , Cavaleiro Albano
Published: March 2009

Steels continue to have a preponderant role in mechanical components under all type of wear solicitations namely, abrasion. The ability of micro-scale abrasion test for evaluating the properties of bulk materials has been widely demonstrated. However, only recently this technique was especially developed to characterize thin-coated materials. This study presents results obtained in micro-scale abrasion tests performed on different low and high alloy steels. These steel samples
underwent thermal and chemical (nitriding) treatments with the aim of enhancing their surface hardness. Nitriding parameters were varied so as to obtain different structures (with and without formation of a “white layer” of iron nitrides (ε-Fe2-3N or γ’-Fe4N compound layer). Test conditions such as normal load and concentration of the abrasive medium (SiC particles in distilled water)
were changed in order to obtain a 2 or 3 body wear contact type. Results obtained allowed to compare the specific wear rate ks for the different steels and treatments tested as well as to relate the influence of surface hardness and test parameters on the wear mechanisms.
Phase Formation in Austenitic Stainless Steel A-TIG Welds
Authors: Rodrigues António , Loureiro Altino , Batista António Castanhola
Published: March 2009

The aim of this research is to study the effect of the welding conditions and of an
activating flux on the microstructure of the melted material of autogeneous A-TIG welds, made on austenitic stainless steel AISI 304. The increase of heat-input coarsened the microstructure, changed its morphology and decreased the δ-ferrite content retained in the microstructure. The use of a TiO2 activating flux does not significantly affect the microstructures. A thin layer tends to form in the surface of the welds, which microstructure and ferrite content are different from those observed in its core.
Low-Pressure Injection Molding Processing of AISI T15 High Speed Steel Powders
Authors: Liberati João Franklin , Araujo Filho Oscar O. , Monteiro Waldemar Alfredo , Esposito Iara M. , Nogueira Rejane A. , Ambrozio Filho Francisco
Published: March 2009

Low-pressure powder injection molding was used to obtain AISI T15 high speed steel
parts. The binders used were based on paraffin wax, low density polyethylene and stearic acid. The metals powders were characterized in terms of morphology, particle size distribution. The mixture was injected in the shape of square bar specimens to evaluate the performance of the injection in the green state, and then sintered. The samples were injected under the pressures of 0.4, 0.5 and 0.7MPa
and at temperatures varying from 110 to 150°C aiming the optimization of the process. The results of the variation of injection pressure were evaluated by measuring the density of the green parts. Debinding was carried out in two steps: first, the molded part was immersed in heptane to remove the major component of the binder and then heated to remove the remaining binder. A second step
debinding and sintering were performed in a single step. This procedure shortened considerably the debinding and sintering time.
Application of Advanced Multiphase Steels in Crashworthiness Structures: Experimental Study and Constitutive Equations
Authors: Peixinho Nuno , Pinho António
Published: March 2009

This work presents results of tensile testing of advanced high strength steels of interest for crashworthy structures: Dual-Phase and TRIP (Transformation Induced Plasticity) steels. The improvements in vehicle crashworthiness observed in recent years have been closely linked to advanced high-strength steels that are currently being produced or in process of development. Amongst these, Dual-Phase and TRIP steels have presented excellent properties for use in crashworthy structures. For these steel grades an understanding of material behaviour at relevant
strain rates is needed as well as constitutive equations suitable for use in analytic and numerical calculations. For that purpose an experimental program of tensile testing was performed in a range of strain rates of interest for crashworthiness problems: 0.0001 /s to 1000 /s. The test results were used to compare material properties and to evaluate the Cowper-Symonds constitutive equation and
a modified version. Crush tests were performed at different speeds for top-hat and hexagonal tubes manufactured using laser welding and the results discussed in view of energy absorption.
Statistical Modelling of the Particle Size Composition of an Alumina Matrix for No-Cement Self-Flowing Refractory Castables
Authors: Silva Abílio P. , Segadães Ana M. , Devezas Tessaleno C.
Published: March 2009

In the processing of any particulate system (including refractory castables), the finer sized particle fraction (matrix or filler) is mostly responsible for the final system properties. Alumina fine powders were used in this work as raw materials, namely two tabular alumina fractions (–500 mesh and –230 mesh) and a commercial reactive alumina. Statistical modelling and the Response Surface Methodology (Statistica, Mixtures Designs and Triangular Surfaces module)
were used to optimise the particle size composition of the three-component mixtures leading to matrix maximum flowability. The mixing methodology, aimed at minimising the water content, was kept constant. No-cement alumina castables produced with the various fine size powder mixtures, were used to prepare test-pieces. After drying and sintering, their mechanical resistance (MoR), density, porosity, water absorption, thermal shock behaviour and microstructure were evaluated.
The results obtained evidenced the relevance of variables such as the water content per unit specific surface area, needed to reach the self-flow “turning point”, and validated the statistical optimisation method used. Moreover those results showed the existence of a matrix composition range, which favours the formation of a flow-bed that enables the aggregate self-flow.
Formation of Ti-Matrix Composites for Lightweight Structural Components by Mechanical Alloying and Subsequent Annealing
Authors: Trindade Bruno , Caetano Marco , Duarte Nelson
Published: March 2009

In this work, a lightweight Ti-10Mg-5Al (wt. %) alloy for structural components was
produced by mechanical alloying. A metastable α-Ti(Al,Mg) solid solution was obtained after 50h of milling. Diffraction peaks ascribed to the Mg phase were detected in the XRD pattern of the sample heat treated at 600°C. This phase tends to oxidize with the increase of temperature giving rise to MgO. The structure of the mechanically alloyed and 900°C heat treated sample consisted of a Ti(Al) solid solution with dispersed MgO particles in the matrix. Hardness and Young’s modulus
values obtained from ultramicrohardness tests confirm the strength improvement of the Ti-based alloy due to the MgO reinforcement.
Analyses of Composite Structures Behaviour with Embedded Bragg Grating Sensors
Authors: Ramos Carlos A. , Esteves José Luís , Silva Rui A. , Marques António Torres
Published: March 2009

Structural health monitoring of composite structures may be accomplished by measuring strains with embedded optical fibre sensors. In this paper, we present the performance of Bragg grating sensors, which are embedded into a carbon composite laminate and them bonded to the structure in analyse. The paper will briefly discuss the results and compare them with a free fibre Bragg grating bonded in the surface of the carbon composite laminate, with existing electrical strain
gauge installation and with a numerical analysis by the finite element method.
Mechanical Properties of Particle Reinforced Resin Composites
Authors: Ramalho Amilcar , Antunes P. Vale , Braga de Carvalho M.D. , Gil M. Helena , Rocha J.M.S.
Published: March 2009

The objective of the present work is the evaluation of the contents of inorganic particles in the mechanical and tribological behavior of polymeric matrix composites. In order to control easily the production of the specimens, a polyester resin was used as matrix and silica particles were added as inorganic filler. The volumetric particle content was ranged from 0 to 46%. In order to understand the influence of the inorganic load was evaluated the mechanical and tribological behaviors for several percentage of particle content was evaluated. There are several applications of inorganic fillers where their volume percentage is important, namely in dentistry. In posterior restorative resin materials, the particles percentage in volume goes up to 50 or more. In most cases spherical and irregular shaped fillers are dispersed randomly. In the studied composites the filler has irregular shape therefore the connection between the matrix and the particles is more effective.
Function of the shape, concentration degree and particle size of the filler the composite mechanical properties vary greatly. All of these factors influence the mechanical properties of the particlereinforced composite, namely: wear resistance, hardness, flexural modulus, flexure strength and toughness The morphology of the failure surfaces was observed by scanning electron microscopy and the results were widely discussed.
Consolidation of Glass Fibre-Polypropylene Towpregs by Compression Moulding
Authors: Silva João F. , Nunes João Pedro , Marques António Torres
Published: March 2009

In this work a theoretical model describing the consolidation of glass fibrepolypropylene (GF/PP) towpregs into composites by compression moulding is studied. Such model relates the constant pressure applied by the press to the other processing operational (consolidation time and temperature) and material variables (fibre/polymer content and packing arrangement, matrix viscosity and powder and fibre dimensions). Compression tests were carried at different temperatures and constant press pressures on unidirectional GF/PP towpreg preforms. The experimentally determined displacement/time curves were compared to the model simulations assuming an isothermal consolidation and two
different fibre/polymer packing arrangements, one triangular and the other hexagonal. The results obtained showed that the towpreg consolidation could be successfully predicted using the model under study.
The Influence of the Addition of Ti on the Mechanical Properties of W-S-Ti Coatings
Authors: Evaristo Manuel , Nossa Ana , Cavaleiro Albano
Published: March 2009

In this work, W-S-Ti films were deposited by r.f. magnetron sputtering, using
simultaneously WS2 and Ti targets. The atomic percentage of Ti in the coating was varied from 0 at.% up to 28 at.%. No significant variations in the S/W ratio with the increase of Ti content were observed. The increasing Ti contents in the films led to a gradual loss of crystallinity. Coatings with contents greater than ≈ 16 at.% only presents a broad peak characteristic of amorphous structures. Alloying the films with Ti led to significant improvements in the hardness (from 0.3 to 8.9 GPa).
Also, the adhesive critical load continuously grew with the increase of the Ti content in the films. The wear coefficient of the films dropped more than one order of magnitude with the increase of Ti content whereas the friction coefficient was kept fairly constant with just a small increase in relation to single W-S film. In conclusion, to have a good tribological performance, the addition of Ti to the films should be balanced in order that the increase of the mechanical properties does not lead to
severe loss of the self-lubricant properties.
Laser Powder Deposition of Tool Steels: Strategies Leading to Homogeneous Parts
Authors: Costa Lino , Vilar Rui , Réti Tamás
Published: March 2009

The microstructure and properties of tool steel parts built by laser powder deposition
(LPD) depend considerably on the build-up strategy and on the processing parameters used. This dependence can lead to inconsistent results which may limit the widespread acceptance of LPD. There is, thus, a need for efficient process optimisation tools that take into consideration the complex phase transformations that may occur during the part build-up process and their effect on
final properties. A model coupling finite element heat transfer calculations with transformation kinetic theory has been developed, which allows the microstructure and property distributions in parts produced by LPD to be predicted. Application of this model to the deposition of tool steels not only explains the origin of the heterogeneous distribution of properties usually mentioned in the
literature but also allows designing build-up strategies that consistently lead to homogeneous, high quality parts. Its application to the study of the influence of substrate pre-heating and idle time between the deposition of consecutive layers is illustrated in the present paper.
Calculations of the Thermal Conductivity of Porous Materials
Authors: Fiedler Thomas , Pesetskaya Ekaterina , Öchsner Andreas , Grácio José
Published: March 2009

In this paper, the geometrical effective thermal conductivity of porous materials is investigated based on two different approaches: the finite element method as a representative for numerical approximation methods and an analytical method for 2D homogenised models based on a solution of the respective boundary value problem. It is found that the relative conductivity is practically independent of the specific shape or topology of the inclusions. Only the morphology (closed-cell or open-cell) of the structure slightly influences the conductivity. Furthermore, it is shown that a small perturbation of the circular inclusions of 2D models increases the effective conductivity.
Green and Sintered Properties of Consolidated Mixtures of Mechanically Alloyed and Elemental Al Powders
Authors: Rodríguez José A. , Gallardo José M. , Herrera Enrique J.
Published: March 2009

Mechanically alloyed aluminium, MA Al, powder is difficult to consolidate.
Consolidation often involves complex processing that includes a hot extrusion stage. An alternative consolidation method consisting of a press-and-sinter process has been developed at the University of Seville. Nevertheless, sintered MA Al compacts have a low ductility. In the present work, to improve the ductility of consolidated compacts, hard MA Al powder was blended prior to the consolidation processing with different amounts (10, 20, 30 wt%) of soft unmilled Al powder. The bimodal microstructure (hard/soft) of the final compacts makes it possible to balance strength and ductility values.
Wear Resistance of Powder Hard Metal Inserted Ductile Iron
Authors: Lourenço Nuno , Santos Henrique
Published: March 2009

A continuous effort is being devoted to study the feasibility of improving the wear
resistance of ductile iron components through an insertion of a hard metal powder layer during the casting process. Tests have been run to evaluate the wear resistance of the inserted material, compared to a non inserted ductile iron. The tests have been run in accordance with ASTM G65-94, which specifies
the so-called rubber wheel test. Three different kinds of material have been tested: a non inserted ductile iron, an inserted ductile iron in the as-cast state and an inserted ductile iron with a rectified surface. The tests have been run gradually; each test piece has been taken out from the test apparatus and weighted at different
intervals, from 200 to 6400 wheel revolutions (or 0.1 to 4.4 km of sliding distance); the results obtained show that the non inserted ductile iron presents a loss of weight fifty percent higher than the inserted material. The analysis of the surface of the test pieces after the wear tests has been run under stereo and scanning electron microscopy. The non inserted ductile iron test piece surface has shown an
uniform waviness with a wavelength around half a millimeter and under higher magnification much finer wear marks have been observed. The inserted ductile iron test piece surface has shown the same relief with half a millimeter wavelength but a significant difference has been noticed: the fine wear marks have been observed in the metallic matrix of the insert but they stop in the neighborhood of the tungsten carbide particles, leading the authors to propose that these hard particles remained unchanged until the metallic matrix supporting them has been sufficiently
removed to cause the respective extraction; this behavior should explain the smaller weight loss rate of the inserted material.
Development of an Optic Fibre Sensor System for Acoustic Emission Sensing in FRP
Authors: de Oliveira Rui , Frazão Orlando , Santos José L. , Marques António Torres
Published: March 2009

In this study an optic fibre system for health monitoring of fibre reinforced plastics was developed. It is based on the detection of acoustic emission (AE) waves in a loaded material. A low-finesse Fabry-Pérot interferometer sensor is used as alternative to the conventional piezoelectric transducers for AE waves sensing. An original procedure for optical fibre sensor interrogation is proposed.
Non-Conventional Injection Moulding of a PP/PC-ABS Blend
Authors: Bilewicz Marcin , Viana Julio , Cunha António M.
Published: March 2009

This paper summarizes the processing, morphology and mechanical properties of PP/PCABS blend produced by a non-conventional injection moulding technique: shear controlled orientation in injection moulding, SCORIM. This technique consists on the in-mould shear manipulation of the melt during the solidification phase by using a special mounted mould plate equipped with two external hydraulic pistons. In this work attention is mainly concentrated on the effect of the processing conditions on the mechanical properties of 70/30 (%/w) PP/PC-ABS blend obtained by direct injection moulding. The SCORIM technique was used deliberately to induce a
strong anisotropic character of this processed polymer-polymer composite that features a complex morphology, featuring outer highly oriented multi-layers and a less oriented core. Different settings of the operative variables were used according to the moulding program based on a design of experiments array (melt temperature, stroke time, number of strokes), assuring a wide processing window. The fracture surfaces of the mouldings were characterized by scanning electronic microscopy. The mechanical properties were assessed by tensile, flexural and fracture tests. The
main significant processing variables determining the mechanical properties of the mouldings were identified together with their effects.
Influence of Diene Content on the Photodegradation of Ethylene-Propylene-Diene (EPDM) Elastomers
Authors: Botelho Gabriela , Queirós Arlete , Silva Manuela A. , Conceição Maria João
Published: March 2009

The photodegradation of EPDM based on dicyclopentadiene was followed by FTIR
spectroscopy and the main photo-oxidation products were identified by derivatization reactions. It could be found that the photodegradation is initiated at the diene with formation of α,β–unsaturated carbonyl compounds and is then propagated to the ethylene-propylene segments. The propagation reactions are accelerated and, hence, the rate of photodegradation increases with the diene content.
Thermogravimetric Study of Polyethylene Catalytic Degradation by Zeolites
Authors: Machado Ana Vera , Neves Isabel , Botelho Gabriela , Rebelo P.
Published: March 2009

Commercial samples of high density polyethylene were decomposed over faujasites
(FAU) type zeolites (Y-type) using thermal gravimetric analysis (TGA). The catalytic activity and behavior of the FAU-zeolites catalysts were determined. It was found that the degradation temperature of polymer strongly depends on the catalytic acidity of the zeolites. HY zeolite was identified as the most active catalyst due to its strong acidity. The results showed that the activation energy decrease with the amount of catalyst added.
Electromechanical Characterization of a Biosensitive and Electroactive Polymer Membrane
Authors: Inácio Paulo , Marat-Mendes José N. , Dias C.J.
Published: March 2009

Most piezoelectric biosensors normally use crystals, as in the quartz crystal
microbalances or surface acoustic wave devices. A new system is described in which piezoelectric polymer films (made of polyvinylidene fluoride, PVDF, and Immobilon, a porous type of PVDF) are used to produce a mass sensitive oscillatory resonant device. Recent results demonstrated that this system successfully detects the binding between bovine IgG (immunoglobulin G) and anti
bovine IgG. In order to improve the performance of the biosensor the electromechanical behaviour of such film-membrane is being studied. Miniaturization is also a desirable trend which will be pursued. Thus reports on the dependence on the electrical, mechanical and biological properties with the size of the film will be presented.