Resumo em Inglês:

Powder thixoforming (PTF) was a promising processing technology that can be used to fabricate high strength particle reinforced aluminum matrix composites, and a pioneer 6061 matrix alloy was fabricated utilizing PTF to investigate its solution treatment behaviors. A comparison study with traditional permanent mold cast (PMC) 6061 alloy disclosed that PTF alloy showed significantly reduced pore amount with only 0.16% (3.50% for PMC alloy). During solution treatment, PTF alloy displayed a much quicker solutionization progress than PMC alloy because of coarse eutectic phases and primary dendrites in latter alloy, its peak values of 14.5%, 241 MPa and 195 MPa in elongation, ultimate tensile strength and yield strength were achieved at 560ºC, an enhancement of 81.3%, 33.9% and 97.0%, respectively, compared with as-fabricated alloy. The dissolution of eutectic phases plays a dominative role in the growth of the primary α phases and secondarily primary α phases within 535ºC. However, the coarsening after 535ºC is subject to a mixture model involving atom diffusion along grain boundaries and through the crystal lattice. The superior tensile strengths of PTF alloy than PMC alloy resulted from decreased grain size, enhanced solid solution strengthening, reduced porosities and decreased harmful effect of insoluble phases in PTF alloy.

Resumo em Inglês:

The effects of shot peening treatments on the microstructure and fatigue behavior of the teeth root in wet copper-based powder metallurgy friction plates were investigated and an efficient method for selecting optimal shot peening parameters for friction plates was proposed. Different experimental processes including microscopy observation, microhardness, roughness and X-ray diffraction measurements have been performed to characterize the treated surface of specimens. It is found that fatigue life of friction plates firstly increases and then decreases with the increase of Almen intensity, and the optimal fatigue life has improved over 55%. It is considered that both surface grain refinement and high residual compressive stress are the main ingredients responsible for the improved fatigue life. With further increase of Almen intensity, surface roughness of the teeth root gradually increases to a critical point, where rough peened surface may induce crack initiation due to stress concentration, and finally lead fatigue deteriorate.

Resumo em Inglês:

The relatively high production costs of innovative materials with tailored properties such as Tailor Welded Blanks, Patchwork Blanks, Tailor Heat Treated Blanks and Tailor Rolled Blanks are responsible for a growing interest in new cost-effective production methods. One of the promising energy-saving and environmental friendly technologies for the production of tailored blanks is twin-roll casting. In the study a new alternative method for twin-roll casting of strips with profiled cross-section is proposed, which uses one or more preloaded endless steel strips with an antiadhesive coating for profiling of the formed strip on a pair of the common cylindrical shells. As a primary stage for the practical process design, numerical simulation of the process using the finite element software package ANSYS is realized. In this way, dependencies of the strip elements outlet temperature, deformation zone length and elements outlet speed on the varied strips thickness and total solidification-deformation zone length are established. Based on the simulation results, a procedure for the twin-roll casting process design is suggested.

Resumo em Inglês:

Polyacrylic acid (PAA)/clay mineral (SWy-1) nanocomposites were prepared by intercalation in solution and their photostability was evaluated. For the nanocomposite films containing 5, 10 and 20 wt % in SWy-1 mass occurred intercalation along with some clay exfoliation, while for PAA/30%SWy-1, the intercalation of PAA chains into the clay interlayers was observed. Scanning Electron Microscopy (SEM) images of the films suggested that nanocomposite films are homogeneous, indicating efficient dispersion of the polymer matrix into the SWy-1 clay. The thermal degradation temperatures of depolymerisation for the nanocomposite films were higher (362-370 °C) than pure PAA (361 °C), which means that the presence of SWy-1 clay promotes thermal stabilization.The photooxidative degradation of pure PAA and nanocomposite films was followed using Size Exclusion Chromatography (SEC). The degradation rate constant for pure PAA was higher than nanocomposite films; therefore, the increase of SWy-1concentration detained the degradation of PAA. The presence of SWy-1 clay contributes for the photostabilization of the material. SWy-1 has ability to disperse the incident light as well as also to absorb part of the UV light instead of PAA, hence minimizing the degradation rate.

Resumo em Inglês:

Lubricated pin-on-disk sliding wear tests were performed on applied to Al-0.1Mg-0.35Ni-Si Alloy by using the spray coating method has been investigated. Different loads were 5, 10, and 15 N at a sliding velocity, 1.32 m/s at room temperature and 60% relative humidity. The surfaces were analyzed by using X-ray diffraction the residual (XRD), energy dispersive (EDS), scanning of (SEM) and (AFM), respectively. The results have showed that the thickness of Cr2O3 coating was significantly related under the identical cold spray condition. These methods have contributed much of the understanding of quality and properties of surfaces. The (Cr2O3) coating has great potential as a wear-resistant. The hardness increased from 102 ± 5 HV to 116.4 ± 2.5 HV at coating thickness 45 µm and friction coefficient reduced from 0.29 to 0.24; and the wear rate was about 2.11X10-13 m3N-1m-1 while hardness was increased from 102 ± 5 HV to 108 ± 3.5 HV at coating thickness 15 µm. The friction reduced from 0.31 to 0.29 at same coating thickness alloys, and the wear rate was about 2.73X10-13 m3N-1m-1. The tribological properties of Cr2O3 coating have exhibited low friction and beneficial to improve the adhesion which was clear on worn surfaces of Cr2O3 coating. Crack, powder flocculation and powder formation are caused by the wear mode of the surface. Brittle fracture was found; while, adhesion and oxidation are the main mechanism of wear during the test.

Resumo em Inglês:

The kinetics of annealing to transform stoichiometric SrTiO3 insulator into a vacancy-doped semiconductor-superconductor was revisited by in situ electrical resistivity measurements. SrTiO3 single crystals were grown by Floating Zone Method. Using a homemade apparatus several electrical resistivity as a function of time were measured at different temperatures, which allows one to study the creation of vacancies during annealing under vacuum. The activation energy for the oxygen vacancies formation/charge doping in SrTiO3 was estimated as 1.4±0.3 eV using solid-state kinetics approach.

Resumo em Inglês:

The aim of this study was to develop a novel, simple and fast route to prepare ZnO nanorods (NRs) -Au nanoparticles (NPs) hybrids directly supported on a substrate to be used in gas sensor devices. The ZnO NRs were promptly grown on interdigitated Au electrodes Al2O3 substrates by chemical bath deposition at a low temperature. After that, Au NPs were deposited by sputtering. Results obtained by XRD, SEM, EDX and TEM showed the perpendicularly aligned growth of the ZnO NRs with a hexagonal base on the substrate and the Au NPs homogeneously covered the ZnO NRs surface. The ZnO NRs-Au NPs hybrids-based sensor exhibited an improved sensor response for H2 and O2 gases compared to the ZnO NRs at 300 ºC. Due to the ability to prepare homogeneous hybrids with high surface directly supported on the substrate; the developed route might provide a convenient approach to preparing gas sensor devices.

Resumo em Inglês:

The Friction Stir Welding Process (FSW/P) is an innovative technique to join metals using the plasticity, not occurring the melting. It was initially applied in aluminum alloys, but recently it has been extended to other materials, for example, copper, steel alloys, polimers and others. In this work it is analyzed the thermo mechanical modelling of the energies involved in the FSW process, performed using AA2024-T3 Alclad aluminum alloy. The temperature of the process surface was also calculated in the interval where it was not measured by type k thermocouples, visual inspection, forging force and energy per weld length analysis were also performed. The equations developed in this work were able to describe the behavior found in the experimental data of temperature and energy per weld length, which allows concludes that can be used to define any temperature point in a region of interest.

Resumo em Inglês:

Polycrystalline mixed Cu-Zn spinel ferrites with general formula Cu1-xZnxFe2O4 (x = 0.0, 0.1, 0.3, 0.5 and 0.7) have been prepared by solid-state reaction method. The effect of Zn2+ ions on transport properties such as DC and AC resistivity, dielectric constant and dielectric loss tangent has been presented in this paper. The resistivity increases with Zn content and decreases with frequency which have been explained by Verway's hopping mechanism. Decrease of DC electrical resistivity with increasing temperature has been observed and activation energy has been found to increase with increasing Zn content. The dielectric constant is found to decrease with increasing Zn content as well as increasing of frequency has been explained on the basis of space charge polarization. In this communication, an attempt has been made to explain the conduction mechanism of Cu-Zn ferrites on the basis of electronic hopping frequency between Fe2+ and Fe3+ ions.

Resumo em Inglês:

MgAl2O4 is a humidity sensing material, which high melting point requires high sintering temperatures. In this work, manganese oxide was used as a sintering aid to obtain MgAl2O4 samples sintered at 1350°C with a microstructure suitable for humidity sensing. Impedance spectroscopy analyses were performed at several levels of relative humidity, indicating that this correlation is possible within the range of 10-80% of relative humidity.

Resumo em Inglês:

A comparative investigation on the microstructural morphologies and hardness values of Cu-35 wt.% Zn and Cu-30 wt.% Zn with 1.5 wt.% Al content is provided. Distinctive specimens by using traditional investment casting were produced. Specimens withdrawn from distinct locations along the castings were thermally and microstructural analyzed. Thermally and chemically induced microstructural modifications affecting the microstructure and hardness are discussed. It is found that components (specimens) located at different positions along of the pattern tree casting have distinctive hardness values. This is associated with Cu segregation and cooling rate. It is also found that solidified piece under a cooling rate ~0.12 K/s has hardness 20% higher than the specimen solidified under 0.07 K/s. Duplex brass with Widmanstätten structure constitutes the resulting microstructure array. This seems to be associated with Al content, while both Zn and Al contents are associated with cooling rate as responsible parameter to induce Widmanstätten structure formation.

Resumo em Inglês:

The present contribution studies on the composition dependence of the electronic and optical properties of the zinc-blende alloy system AlPxSb1-x. The calculations are performed using a pseudopotential approach under the virtual crystal approximation. Features such as electronic band structure, energy band-gaps, refractive index, dielectric constants and valence and conduction charge densities are determined and their compositional dependence are examined and discussed. The aim of this paper is to provide new data for electronic and optical properties by varying the alloy composition x and to see to what extent the compositional disorder affects the properties of interest. The effect of alloy disorder on the energy band-gaps and electron charge densities is found to be important for getting a meaningful agreement with experiment. Our results show a direct-band gap bowing parameter of 2.7 eV which agrees very well with experiment. Moreover, a transition between indirect band gaps is found to occur twice. Besides, bonding and ionicity are discussed in terms of electron charge distribution. The information derived from the present study can be useful for optoelectronics applications.

Resumo em Inglês:

Corrosion inhibition nature of Colocid dye on the corrosion of mild steel in acid media was analyzed using weightloss and electrochemical methods. The results of electrochemical and weightloss studies indicated that Colocid acid could act as a potential inhibitor for mild steel in acid media. It has been observed that the inhibition efficiency increases with inhibitor concentration and the inhibition efficiency of Colocid acid dye for the corrosion of mild steel in 1.0 M HCl solution is larger than that in 0.5 M H2SO4 solution.Potentiodynamic polarization studies showed that the dye molecule is of mixed type inhibitor. The adsorption of the compound on the mild steel surface obeyed Langmuir adsorption isotherm. The potential of zero charge was measured to find corrosion inhibition mechanism in these media.

Resumo em Inglês:

A new approach to a single crystals growth of the iron sulfide phases of definite structure and nonstoichiometry is developed and applied. This approach is based on the method of crystal growing from solution melts. This approach is based on the crystallization or recrystallization of iron sulfides from iron sulfide solutions in iron dihalide melts under fixed sulfur vapor pressure in the closed system in non-isothermal (two-temperature) conditions. It allows to regulate the composition and structure of the resulting iron sulphide. In particular, at a relatively low pressure (<0.4 atm), pyrrhotite with a trigonal 3T structure is synthesized. At higher pressure pyrite β-FeS2 is grown. Reaction scheme for the formation of iron sulphides based on the reversible oxidation of sulfur by iron dihalide is proposed and substantiated. On the base of the {pyrite + marcasite} - mixture annealing under the melts of the deepest eutectic compositions of KCl - FeCl2 and NaCl - KCl - FeCl2 systems, the instability of the marcasite phase regarding the pyrite one (at least, for T ≥ 340°C) was shown.

Resumo em Inglês:

In this work, biocomposites of poly (3-hydroxybutyrate) (PHB) / calcium carbonate from Rhea Americana eggshells were prepared and the effects of the addition of the inorganic filler in the polymeric matrix were assessed. The residue (powder) of the eggshell calcined at 400 ºC or in natura was inserted into a PHB solution for preparation of films via casting. Powder samples were characterized by X-Ray Fluorescence (XRF), X-Ray diffraction (XRD) and Thermogravimetry (TG/DTG) and films were characterized by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM) and biodegradation tests according to the ASTM G 160-03 norm: the results were reported as weight loss and visual inspection by optical microscopy (OM). From the results of the XDR, it was perceived that the peaks in the diffractograms of the powder obtained by milling the Rhea Americana eggshells corresponded to the diffraction patterns of the Calcite crystals, which is a calcium carbonate polyform, and that the calcination preserved the crystalline structure, maintaining the calcium carbonate in the samples. For the biocomposites, a peak characteristic to the calcium carbonate in 29.57º was detected, indicating the insertion of the filler to the polymer matrix. Through SEM the presence of small agglomerates, probably due to polymer particles that were not dissolved, was observed for the pure PHB film. With the addition of the filler in natura a greater porosity was formed in the surface of the biocomposite films, and with the calcined filler, homogeneous films with reduced porosity were obtained. From the weight loss and OM results, it was observed that the filler inserted into the polymeric matrix catalyzes the biodegradation process up to 60 days evaluation in different ways, depending on the type of sample used.

Resumo em Inglês:

GH 909 alloy is a kind of low thermal expansion superalloy with high strength and low expansion coefficient. It is mainly used for manufacturing of aero-engine turbine casings, sealing ring, vanes and other gap control parts, to improve the working efficiency and thrust of the engine as well as to reduce gas loss and fuel consumption. However, the machinability is still a problem that restricts the application of GH909. This paper investigated the machinability referring to cutting forces, surface quality and tool wear in the milling process with carbide tool. The main conclusions are: (1) GH909 has similar machinability with other Nickel-based alloys, cutting velocity does not have great influence on cutting forces for small radial cutting depth. (2) Good machined surface quality can be get for cutting velocity around 70m/min. (3) To get good tool performance and reduce tool wear rate, cutting velocity can be set to no larger than 80m/min.

Resumo em Inglês:

New empirical relationship is proposed to calculate instantaneous maximum diameters on the sample during compression test. The proposal is a relationship between instantaneous maximum diameter, friction coefficient, initial dimensions of the sample and the displacement during the compression test. Seventeen compression tests were carried out to copper cylindrical samples without lubrication at room temperature to obtain this new empirical relationship. Numerical simulations were carried out taking into a count this new relationship for numerical validation. The maximum diameters calculated with this new empirical relationship are the same to the experimental measurements. The mechanical behavior calculated with this new relationship and with the friction corrections of Rowe and Dieter are similar. The simulations are similar to the experiments, with differences lower than 4.21%. The simulation shows higher hardening in the middle of the sample than on the bottom. Numerical simulations show that, possibly, the friction coefficient between sample and dies changes meanwhile the sample is hardening.

Resumo em Inglês:

Microtubules were constructed by covering the fungus Aspergillus aculeatus sequentially with silver and gold nanoparticles, resulting in a stable hybrid mesostructured material that presented three distinct regions containing different combinations of silver and gold nanoparticles. These heterogeneities were determined by the hyphal growth since the impossibility to cover the dead fungus, which suggests the influence of the secondary metabolites produced by living fungus in the deposition mechanism.

Resumo em Inglês:

Porous Ti/HA nano-composite was prepared for implant fixtures and in situ formation of Hydroxyapatite. At first, Ca(OH)2 nanoparticles were synthesized by precipitation. Raw materials included Ca(NO3)2.4H2O, NaOH, a mixture of deionized water and ethanol. Synthesized Ca(OH)2 nano powder was mixed with (NH4)2HPO4 and the mixture was calcined at 700 ºC for 30 min. After calcination, Ca2P2O7 and CaPO3(OH).2H2O were synthesized with imperfect hexagonal morphology. The resulting powder was mixed with pure titanium powder and pressed under 300, 500 and 700 MPa. The samples were sintered at 1000 ºC for an hour under pure argon. Final composition was Ti/HA with hexagonal morphology. XRD and SEM showed the in situ formation of nano hydroxyapatite besides titanium phases during the sintering procedure. The density and open porosity of the 700 MPa pressed-samples were 3.07 g/cm3 and 28.2%, respectively. In general, porous Ti/HA nano-composite with suitable porosity could be successfully synthesized by co-precipitation procedure.

Resumo em Inglês:

Dissimilar Al-Cu joints are desirable due to the combination of the good electrical and thermal properties of copper with the economic advantages of aluminium. However, different chemical, mechanical and thermal properties turn dissimilar welding into a challenge with traditional fusion welding techniques. Friction stir welding appears to be a good alternative to welding dissimilar materials. Most of the works in Al-Cu FSW have been performed with Al on top. This work investigates the influence of heat input on the shear strength of aluminium-copper lap joints produced by FSW with a copper over aluminium lap configuration. Welds produced with the ω/ν rate of 200 rev.mm-1 or 500 rev.mm-1 resulted in the melting of the base materials and material leaking. Joints with shear tensile strength varying from 76 to 85% of the original resistance of AA6060 T5 were produced when the ω/ν rate was varied from 80 to 110 rev.mm-1. The fracture was governed by tension overload on the aluminium sheet, resulting in little influence of welding defects, such as tunnelling, on the joint strength.

Resumo em Inglês:

Nanoparticles of TiO2 have been the main semiconductor applied in Dye-sensitized solar cells (DSSCs). In this work, titanate nanotubes (NaTiNT) and nanoribbons, were obtained by the hydrothermal method from TiO2 anatase. These materials were deposited on conductive substrate by electrophoresis, with and without thermal treatment, sensitized by ruthenium-based dye and used as work electrode. Exposing those photovoltaic devices to visible radiation, with films before thermal treatment, a short-circuit current density (JSC) of 0.0012 mA/cm2 was observed for the cell with NaTiNT, a current density of 0.0398 mA/cm2 for the cell with Nanoribbons, and a current density of 0.4028 mA/cm2 for the cell with TiO2 as electrode. After thermal treatment, a short-circuit current density of 0.4269 mA/cm2 was observed for the cell with NaTiNT, a current density of 0.0765 mA/cm2 for the Nanoribbons cell, and, finally, a current density of 0.3310 mA/cm2 for the cell with TiO2 as electrode. The new morphological, structural and optical characteristics of these nanoparticles may contribute for the development and research of new generation photovoltaic devices.

Resumo em Inglês:

The aim of the present study was to determine the phase relations in the Tl4PbTe3-Tl9TbTe6-Tl9BiTe6 section of the Tl-Pb-Bi-Tb-Te system. Based on a set of the methods of the physicochemical analysis (differential thermal analysis, powder X-ray diffraction method as well as microhardness measurements), the phase diagram of the Tl4PbTe3-Tl9TbTe6 boundary system, some isopleth sections, liquidus and solidus surfaces projections, as well as isothermal sections at 840 and 860 K, were plotted. Unlimited solid solutions with the Tl5Te3 structure (δ-phase) were found in the system, which are of interest as a thermoelectric materials.

Resumo em Inglês:

A gray cast iron disc, which had been submitted to a heavy duty automotive brake test, was examined with energy filtered transmission electron microscopy. A graphite flake in a convenient angular position showed the shear interaction of graphite layers with the iron matrix in nano-scale resolution. Atomic layers of graphite were wedged into the ferritic bulk, allowing the entrance of oxygen and the subsequent formation of magnetite. The exfoliated few-layer graphene batches deformed heavily when forced into the matrix. When Raman spectra from the disc surface, which show distinctive carbonaceous bands, were compared with Raman spectra from graphite subjected to deformation in a shaker mill with different milling times, it could be seen that the shear stress on the brake surface was much more effective to induce disorder than the milling, where compressive and impact forces had been additionally exerted on the sample. During shear load the high anisotropy of elastic modulus in the graphite crystalline structure and the low adhesion between graphite basal planes allowed the exfoliation of wrinkled few-layer grapheme batches, causing the formation of more defect related Raman bands than the mechanical stress during high-energy milling.

Resumo em Inglês:

Ti-6Al-4V alloy is employed in implants because of its good mechanical strength, excellent biocompatibility, and good resistance to corrosion in biological environments. Herein, a composite (HAp-TiO2, 50% by volume of both components) coating surface employing Ti-6Al-4V was characterized. Samples were analyzed post fabrication and post heat treatment to analyze the coating recrystallization, phases, crystallinity, porosity, and roughness. The coating showed rutile crystalline and amorphous Hap phases with crystallinity, porosity, and roughness of 55.6%, 13.6 ± 1.0%, and 4.2 ± 0.6 µm; whereas, after heat treatment, it showed a rutile hydroxyapatite phase and β-TCP with values 75.6%, 13.9 ± 1.9%, and 3.8 ± 0.2 µm, respectively. The composite exhibited 874 ± 26 HV100 hardness and 30 ± 2 MPa adhesion strength after heat treatment, which agree with previously reported data on other bioactive coatings. Therefore, this composite becomes much more crystalline after heating at 750 °C for 1 h.

Resumo em Inglês:

The replacement of electrolytic hard chrome (EHC) by high velocity oxy-fuel (HVOF) sprayed coatings is investigated due to the toxicity of EHC process. The wear behavior of AISI 4140 steel coated by HVOF-, EHC-process was compared to quenched and tempered (Q&T) steel using a pin-on-disc apparatus. The wear tests were conducted at room temperature, 10 N applied load and 0.1 m/s sliding speed in dry condition. The results were interpreted on the basis of the microstructure and hardness. Wear micromechanisms were investigated by SEM. The predominant presence of the WC phase and the formation of W2C and W3C phases, associated with decarburization of superheated regions of the CoCr binding phase of HVOF-coated samples were observed by X-ray diffraction analysis. Wear tests results show that the WC-10Co-4Cr coating exhibits better wear resistance than the EHC coating and Q&T steel. The formation of a wear resistant tribolayer was determinant to the excellent wear behavior of the thermally sprayed coating.

Resumo em Inglês:

Friction welding is a solid state technology which has been used worldwide. Potential advantages may be recognized as reducing welding project costs, weld weight, environmental impact and to promote enhanced mechanical properties. However, traditional welding methods are still a common practice in many engineering areas. In this sense, this work aims to present the technical advantages for replacing gas metal arc welding (GMAW) by friction welding for joining hydraulic cylinder tubes. The feasibility of friction welding was demonstrated by microstructural analysis, mechanical properties and hydrostatic pressure testing. The results showed enhanced mechanical properties for the friction welded tubes. In addition, macro and microstructural features presented distinguishable process characteristics which reflect in different microhardness values. The friction weld exhibited a better behavior in bending as well as hydrostatic tests.

Resumo em Inglês:

Carbon thin films deposited by the magnetron sputtering technique were evaluated by Raman spectroscopy to study the influence on their crystallinity caused by different parameters like the carbon deposition time, the different buffer-layers and substrates employed and also two distinct heat treatments. The present results showed that the choice of these parameters plays an important role in the production of these films. The results also indicate the possibility of using the technique for the production of carbon thin films to be employed in future in applications with controlled content of structural defects, predominance of ordered sp2 bondings and tendency of graphitization.

Resumo em Inglês:

A nanostructured SnTe phase was produced by mechanical alloying after 2 h of milling. Part of the as-milled powder was annealed and its X-ray diffraction (XRD) pattern was recorded. The XRD patterns of the as-milled and annealed samples were refined using the Rietveld method. After annealing, partial decomposition of the SnTe phase was observed and corroborated by estimating the mean crystallite size using a Willianson-Hall plot. The Cowley-Warren parameter αSnTeCWfor the first coordination shell was calculated, showing a preference for homopolar pairs. This preference is consistent with the partial decomposition observed. According to the optical absorbance spectra, the band gap energy is inversely proportional to crystallite size, following a decaying exponential function. From the photoacoustic absorption spectroscopy measurements, the thermal diffusivity parameter and the transport properties of as-milled and annealed SnTe powder were determined.

Resumo em Inglês:

In this investigation, an attempt has been made to fabricate dissimilar thickness corner joint using non-heat treatable (AA5086) and heat treatable (AA6061) dissimilar aluminium alloys by friction stir welding process with plate thicknesses of 6mm and 4mm. Three parameters and three levels were considered to conduct the experiments such as welding and rotational speeds of 100, 150 and 190 mm/min and 900, 1000 and 1100 rpm and plunge depth of 0.1, 0.2 and 0.3 mm. The mechanical properties were evaluated using hardness and tensile tests. Taguchi grey relational analysis was carried out to determine the optimum process parameters. The higher value of tensile strength was obtained 192 MPa at rotational and welding speeds of 1000 rpm and 150 mm/min which was 76.80% of parent material and maximum hardness was 157 HV at thermomechanically affected zone for the rotational speed of 1100 rpm and hardness at stir zone was maximum because of refined grain formation. The microstructures of various regions were observed and analyzed by optical and scanning electron microscopes. The tensile samples fractured at the heat affected zone. The spindle motor current consumption, work material temperature distribution, and force generation during friction stir welding were estimated and analyzed.

Resumo em Inglês:

Effect of Fe, Ni and Cr addition on the wear behavior of hyper-eutectic Al-Si automotive alloy has been studied. Dry sliding wear tests have been conducted using pin-on-disc wear testing machine under normal loads of 20N and constant sliding speed of 0.64 ms-1. Influence of Fe addition to the base alloy increases the wear rate due to the formation of needle beta intermetallics. Ni addition to the alloy does not impede formation of needle-like intermetallic compounds and has no positive effect on the modification of microstructure. Introducing of Cr to the iron-rich alloy changes the beta intermetallics into the modified alpha phases and therefore reduced the detrimental effect of iron. As a result it recovers the strength and wear properties of the experimental alloy. Wear test surfaces were examined by SEM and have shown that Cr added alloy improves wear resistance through mild and smooth abrasive grooves filled with oxides.

Resumo em Inglês:

Three different compositions of high-Si Al alloy pipe, with a gradient structure, were produced through semi-solid rheological squeeze casting, the microstructural characteristics of which were investigated. The mechanism of gradient structure formation and the effect of acicular Fe-rich phases on liquid segregation were revealed. Meanwhile, the crystal structures of the Al4FeSi2 and Al15(Fe, Mn)3Si2 phase were elucidated. The relationship between the volume fraction of hard particles in the pipe wall and the macro-hardness was established. Wear resistance tests of the inner surfaces of the pipe walls, and tensile strength tests at different positions around the pipe walls, showed that the δ-Al4FeSi2 phase (acicular Fe-rich phases) reduced the wear resistance and the tensile strength of the alloy. In this study, the gradient distribution of the hard particles caused the outside of the pipe wall to have a higher tensile strength.

Resumo em Inglês:

The purpose of this study is the surface modification of Ti10Mo8Nb experimental alloy by using TiO2 nanostructure growth. Ingots of the Ti10Mo8Nb experimental alloy were produced by fusion from sheets of molybdenum, niobium, and titanium commercially pure in an arc melting furnace under argon atmosphere. The potentiostatic anodic oxidation was performed using an electrolyte formed of glycerol and H2O (1: 1 by vol.) with the addition of 2.7% (w/v) NH4F under 20 V for 3 h at room temperature. After the surface treatment, the samples were annealing. The surface of the alloy was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), contact angle, surface energy measurements. In vitro studies, such as cell and bacterial adhesion, were performed to evaluate the response of this treatment. The Ti10Mo8Nb alloy exhibited beta phase after the processing. After the surface treatment, a nanoporous layer of TiO was obtained. The anatase phase was found in the annealed samples (450 ºC for 3 hours). In vitro analyzes showed cell growth viability and decreased bacterial proliferation due to the larger specific surface area.

Resumo em Inglês:

Dye-sensitized solar cells (DSSCs) are a feasible option for photovoltaic energy. Zinc oxide is an n-type semiconductor employed as photoanode on DSSCs. ZnO thin films were electrodeposited to study the effects of different potentials applied during deposition. SEM images, XRD and UV-Vis analysis were conducted to reveal the morphologic, structural and optical properties of the films at three potentials. DSSCs were assembled and the photovoltaic parameters were obtained through J-V plots. DSSC with 0.031% of efficiency was demonstrated at -1.4 V of deposition potential.

Resumo em Inglês:

The purpose of the present work is to understand the evolution of residual stresses in weldments. The study made to weld the multipass dissimilar of Nickel-based superalloy Inconel 625 and stainless steel 316L using Continuous Current Gas Tungsten Arc Welding (CCGTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) process employing ERNiCrMo-3 and ERNiCr-3 fillers. The L4 orthogonal array was used in the present experimentation process. Analysis of Variance (ANOVA) is applied for the optimization and to identify the critical parameters. In welding process, the size of the lattice size will be stressed due to welding parameters; the lattice dimension is measured by non-destructive technique X-Ray diffraction to investigate residual stress in the weldment in the lateral surface of the plate. X-Ray Radiography test has evaluated the quality of welds. The results show that root gap is a critical parameter and filler wire and weld processes are not critical.

Resumo em Inglês:

The Young's modulus (E), Poisson's ratio (ν) and anisotropy parameter (AG) of α' phase, which obtained from different solution treatment and water quenching temperature, were investigated using first-principles calculations based on density functional theory (DFT). The calculation results showed that the Z-axis value of the elastic modulus of α' phase was higher than that of the X-axis and the Y-axis, indicating the elastic modulus of α' phase was anisotropic. It was decreased with increasing the solution treatment and water quenching temperature for the elastic modulus anisotropy of α' phase. In order to verify the calculation results, the elastic modulus anisotropy of macroscopic Ti-6Al-4V alloys, which were treated at 850ºC, 900ºC and 950ºC, were tested by the tensile and the compressive experiments. The experimental results showed the same change tendency with the calculation results. It concluded that the elastic modulus anisotropy of macroscopic alloy could be controlled by the elastic modulus anisotropy of α' phase.

Resumo em Inglês:

Inconel 625 is a nickel-based highly-resistant superalloy widely used in aerospace components, in the nuclear industry, and especially in the maritime industry. Materials such as Inconel 625 have been widely used in oil exploration of Brazilian pre-salt layers due to their excellent resistance to corrosion under tension, pitting and crevice corrosion by chloride and sulphide ions, and also because they are resistant to microbiological corrosion. All components used in the exploration of crude oil in these environments suffer mechanical fatigue from oceanic oscillations that naturally occur. Samples were precisely machined and tested under uniaxial tension and cyclic tension-compression fatigue following determinations of the ASTM E8M and ASTM E466 standards respectively, at a loading ratio of R = -1. Tensile strengths of 586, 472, 382 and 306 MPa were selected according to the yield strength of the material for raising the S-N curve. A macro and microstructural characterization regarding failure modes was performed revealing that fatigue striations predominated in the stable region of crack growth, whereas microvoids coalescence prevailed in the fast fracture zone. Inconel 625 presented a refined microstructure composed of equiaxial grains with a mean size of 14 µm, typical of refining obtained by hardening followed by recrystallization. The precipitation of MC type carbides (M=Mo or M=Nb) and Cr23C6 dispersed in the austenitic matrix of Inconel 625 controls a secondary alloy hardening mechanism.

Resumo em Inglês:

The aim of this work was to perform an analysis of the influence of Sodium Fluoride (NaF) on chitosan particles size and morphology produced via ionotropic gelation with higher rotational stirring speed. Samples were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Dynamic Light Scattering (DLS), Zeta Potential (ζ), Scanning Electron Microscopy and Energy Dispersive Spectroscopy (SEM/EDS). Chitosan/TPP particles diameter obtained was in the order of 3.8 µm. When NaF was added in different concentration (0.05%, 0.2% and 2%), the particle size diameter values, Zeta Potential and Poly Dispersive Index measures consequently decreased. Even so, no further modification in morphology was found. An exception was made for the samples with higher NaF concentration. After 21 days, occurred an increase in the particle size diameter. In the future, the proposed methodology could provide a dentistry application, especially on delivering particles of NaF.

Resumo em Inglês:

Important properties in cementitious materials, such as concrete, are related to the presence of additives that influence the rigidity and the physical and chemical resistances. For the evaluation of the additive effectiveness, known as pozzolanic activity, a simple procedure, the Chapelle test, is commonly used, and it essentially consists in a reaction between the additive with calcium oxide in aqueous medium. However, such procedure presents limitations in terms of processing time and lack of information regarding the reactions kinetics. In this sense, a simple method based on the kinetic and thermodynamic principles of chemical reactions is proposed, which can be performed using conventional electronic pH sensors. The study provides an alternative methodology with many advantages over the traditional procedure, such as energy and time-savings, more robustness and more confidence. In this paper, three types of silica nanoparticles that can be used as low-cost additives were characterized in relation to their morphology and crystallinity by XRD and SEM, the particles average diameters were obtained and the particles were used for studying the chemical process that takes place during the Chapelle test. Results and the semi-empirical analysis provided strong evidence that the process is an acid-base 1:1 reaction and it was verified that the mean reaction times varied from 64 to 195 min. It is a remarkable result, since the proposed analysis can be performed with simple, fast and low-cost instrumentation and needs only a worksheet software, whereas the Chapelle test takes 16 hours and provides no dynamic information. Besides the limitation that the methodology is not able to quantify and to elucidate the effects of the specific surface area of the particles, which needs a complete BET study, the research provides a significant contribution for the understanding of the pozzolanic process, of great importance in both concrete and ceramic research.

Resumo em Inglês:

Residual stresses on welded joints have been studied by several methods. In this present work, residual stresses was measured by a novel methodology under development named Displacement of Coordinated Points (DCP). To evaluate anisotropy effects in steel plates, two directions of the weld bead were considered: Welding was performed in both parallel and transversal direction of rolled steel plate ASTM A131 grade AH36.The experiments showed higher values of the residual stress in the transversal direction of the lamination when compared with the longitudinal direction, evidencing the anisotropy effect of the material. It was also observed that the increasing in heat input induces higher residual stress.

Resumo em Inglês:

Samples of duplex stainless steel 32205 (standard duplex) and 32304 (lean duplex) were investigated in the as-received state, cold rolling (with thickness reduction of 64 % and 62 % respectively) and after annealing at 1055ºC for 20 s soaking. Crystallographic microtexture was obtained via Electron BackScatter Diffraction (EBSD) technique. The results showed that the crystallographic microtexture of ferrite phase in the as-received, cold rolled and annealed condition were more intense in alpha fiber=<011> // RD and tetha fiber. The austenite microtexture was shown to be, for all conditions, mainly composed by Brass component.