Resumo em Inglês:

The microstructures of high-Si Al alloy cylindrical simples produced by rheological squeeze-casting with bottom-up filling were investigated. The effect of process parameters on the distribution of hard phases (primary Si and Fe-rich phase) was evaluated, and flow characteristics of semi-solid slurry of high-Si Al alloy were investigated. Differences in volume fractions (VFs) of hard phases between the middle and upper layers of cylindrical samples decreased as the squeezing speed increased. Moreover, the flow state of the semi-solid alloy slurry transitioned from laminar to turbulent flow as the squeezing speed was increased. Movement of gases throughout the semi-solid alloy slurry filling process was analysed under different process parameters. The results provide insights for improving rheological casting of high-Si Al alloy and other Al matrix composites.

Resumo em Inglês:

The present work aims to evaluate the metallurgical and mechanical behavior of dissimilar weld formed by 309L-Si and ERNiCrMo-3 (Inconel 625) electrodes combination on the ASTM A182 F22 steel with GMAW process. The welded joints were characterized by SEM, OM, tensile test and Vickers microhardness technique. The dissimilar interface formed in buttery of 309L and INC625 showed partially mixed zone (PMZ) formation and solidification microcracks that affected the mechanical properties in welded joint, presenting a fragile behavior. The F22 and INC625 interface presented high hardness regions with peaks greater than 400 HV. These regions were enriched by carbon due to the diffusion from F22 steel into the weld metal caused by tension relief heat treatment (TRHT).

Resumo em Inglês:

Abstract The article presents the process of modeling delamination of a woven composite material by the finite element method. The models contain a detailed mesostructure in the form of weave geometry. The delamination occurs in the DCB (Double Cantilever Beam) test with the critical energy release rate as a propagation criterion. The methods used, especially Virtual Crack Closure Techniques (VCCT), have allowed us to present the delamination front changes during the propagation. To further investigate the influence of the mesostructure, additional fully homogenous models were analyzed. Load-displacement graphs, typical for DCB tests, are presented. The obtained results show how the presence of detailed geometry of the composite influences the development of damage.

Resumo em Inglês:

Abstract Up to now, plasma electrolytic oxidation (PEO) has been either produced direct current or ultra-low frequency (< 1 kHz) pulsed discharge using high concentration alkaline-silicate electrolytic (Na2SiO3 > 8 g.L-1 with presence of KOH). In order to contribute to these studies, the effect of current pulse width and time duration was investigated using diluted silicate electrolytic (Na2SiO3 2 g.L-1) and high pulse frequencies (> 1 kHz). The PEO process was performed on pure aluminum to try to explain how the phases composing the coatings are formed and distributed over the treatment time. For this, was made in situ monitoring using optical emission spectroscopy (OES) coupled with CCD camera. The crystalline phases evolution in the sample surface was investigated using grazing incidence X-ray diffraction (GIXRD). Regarding the evolution of ceramic phases, it is possible to verify that, internally, the predominant phase is rhombohedral α-Al2O3 but, superficially, the predominant phase is cubic γ-Al2O3. It was verified the presence of Si on the borders of the pores or in proximity to cracks, especially in the treatments with higher pulse width. SEM analysis shows a reduction of the superficial porosity and an increase in coating thickness with pulse width and treatment time.

Resumo em Inglês:

Abstract This work is focused on the failure analysis of a HP40 steel tube used in steam reformer units, which was operated at about 850 °C for 100000 h. The failure analysis was conducted experimentally and numerically using the Thermo-Calc software. The main results indicated that the failed tube presented slightly different contents of Ni and Cr from the nominal ones, which originated the absence of the interdendritic eutectic microconstituent, composed of austenite and M7C3 carbides. This fact was also corroborated by Thermo-Calc results. This absence of eutectic facilitates the crack propagation on the dendritic zones and then the trangranular brittle fracture propagation through the austenite dendritic zones.

Resumo em Inglês:

Abstract The Zn coatings obtained through electrodeposition are used to protect steel substrates from corrosion. In general, organic additives are added to the deposition bath in order to improve deposition characteristics such as corrosion resistance, hardness and deposition efficiency. Despite of the literature present information about the various organic additives effects on Zn coating properties there is no analysis of organic compounds with free electron-containing radicals, such as formic acid and cyclohexylamine. The formic acid has oxygen atoms with free electrons, whereas cyclohexylamine contains nitrogen with free electrons. Aiming at overcoming this gap, this manuscript presents an analysis of the effect in addition of formic acid mixture and cyclohexylamine on the deposition flow efficiency, corrosion resistance, hardness, roughness and micro-structure of Zn coating on carbon steel AISI 1020. The corrosion resistance evaluation was performed by potentiodynamic polarization determined by polarization resistance and weight loss tests as well. The analisys of morphology and electrodeposited microstructures were made by the Scanning Electron Microscopy (SEM) and Spectrometry X-Ray Diffraction (XRD). The Zn coatings were obtained from chloride deposition baths at constant pH 5. Results showed that corrosion resistance in the 0.5 mol/L NaCl solution of Zn coatings increases with the addition of the mixture of the formic acid and / or cyclohexylamine. Also, the corrosion resistance is higher with mixture than with additives alone. The addition of the mixture formic acid and cyclohexylamine increases the basal plane presence (0 0 2). However, the basal plane presence (0 0 2) does not increase when formic acid and cyclohexylamine are added alone which indicates a synergic effect of formic acid and cyclohexylamine in in the plan promotion (0 0 2). Also, was observed that an addition of formic acid mixture and cyclohexylamine increases the current deposition efficiency, decreases the roughness and raises the Zn coating hardness.

Resumo em Inglês:

Abstract Over the last decades, alloy 718 usage has expanded and requirements imposed by its industrial applications became more critical. The knowledge about grain boundary character distribution (GBCD) in alloy 718 and its effect on properties improvement is mostly built based on iterative processing through cold rolling steps interspersed with solution annealing. Alloy 718 is found in the industry in many different forms and geometries, and fabricated by multiple thermomechanical processes such as wire drawing, rolling, forging or extrusion. The present study focused on understanding how wires respond to deformation mode related to drawing in regard to GBCD evolution, crystallographic orientation, precipitation of δ-phase and grain size. Lastly, assessing the resulting mechanical properties. The findings show that microstructural evolution is a consequence of competing mechanisms such as strain induced boundary migration, recrystallization, grain growth and phase precipitation. The deformation gradient along wire cross section plays an important role in affecting microstructural features, such as δ precipitation, GBCD and microtexture.

Resumo em Inglês:

Abstract The discussion of the importance of the perpendicular tension strength to better understand the wood’s mechanical behavior in several situations, such as shrinkage analysis, glued laminated beam failure analysis, has become clear that more basic input information on tension perpendicular to grain is needed. This work investigated tension perpendicular to grain properties in three different orientations, for radial, tangential and 45-degree directions, using Sugar Maple specimens, and testing methodology according to ASTM D143. In addition, the influence of the density on tension strength values for each direction was analyzed. Furthermore, the failure modes of radial, tangential and inclined specimens are shown and a numerical simulation is presented in order to verify the tendency of the ruptures. From the statistical analysis, it can be concluded that the experimental results of tension perpendicular to grain strength loaded in the radial and tangential directions show a significant statistical difference. Strengths obtained at 45-degrees differ significantly from the other directions.

Resumo em Inglês:

Abstract In the present work, electromagnetic wave properties of the Fibonacci one-dimention photonic crystal (1DPC) structure consisting of double negative materials incorporated high Tc superconductor are theoretically investigated. It is found that the quasi-periodic structure created a photonic band gap as a periodic structure. We have calculated the transmittance spectra and noticed a wide band gap which can be controlled in it by the thickness of metamaterial, superconductor layer and incidence angle.Photonic band gap became more noticeable by increasing the thickness of the metamaterial and superconductor layers. The structure was affected by changing the incident angle and the band gap width increase with a noticeable shift to short wavelength region. Additionally, the photonic band gap shifted to longer wavelength value with increasing the operating tempeature. Furthermore, we have studied the pressure effects and we found the change in the location and width of photonic band gap.

Resumo em Inglês:

In this work, the optical dynamics and the structural properties of the zinc phthalocyanine which are coated onto 150 nm thick Au substrates are studied by the X-ray diffraction and optical spectrophotometry techniques. The Au/ZnPc interfaces appears to be strongly affected by the large lattice mismatches at the interface. It is observed that the coating ZnPc onto Au substrates increases the light absorbability by 4.7 and 128.2 times in the visible and infrared regions of light, respectively. Au substrates activated the free carrier absorption mechanism in the ZnPc thin films in the infrared range of light. In addition, the transparent Au substrates forced narrowing the energy band gap in both of the Q and B bands. It also increased the dielectric constant value by ~3.5 times in the IR range. The enhancements in the optical properties of ZnPc that resulted from the thin Au substrates make the ZnPc more suitable for optoelectronic, nonlinear optical applications and for electromagnetic energy storage in the infrared range of light.

Resumo em Inglês:

Bioactive glasses (BG) are versatile materials for various biomedical applications due to their capacity to bond to hard and soft tissues. These materials can be produced with different nominal compositions, such that include fluoride ions. Fluorine-containing-BG (BGF) can be produced by the sol-gel method, and its properties can be changed by altering the synthesis parameters. Here, BGF particle size between 235 nm-390 nm were obtained through sol-gel method assisted by ultrasound energy (BGU) or through mechanical stirring (BGM). The BGM and BGU particles showed highly dispersed spherical shape, moreover BGM are mesoporous and BGU are dense structures, indicating mixing mode can alter mainly the material textural characteristics. All compositions have apatite forming ability, verified by DRX from 14 days in SBF. The results showed CaF2 on the surface of BGF particles, indicating that part of F ions was not incorporated in the material network. The samples did not show any cytotoxicity towards human cells in Cellular Metabolic Activity and Calcein assays. This study showed that mechanical agitation was more efficient to produce mesoporous particles to be applied as carrier of drugs and molecules to the biological environment, so BGM can be used as a more efficient biomaterial for such applications.

Resumo em Inglês:

Heat treatments and geometries have a significant influence on the mechanical behavior of endodontic files. Finite element analyses were performed to verify the effects due to each of these parameters in NiTi files. Two designs and three NiTi atomic structures (resultant from different heat treatments) were selected for this study. The geometries of the ProTaper Next X1 and ProTaper Universal S2 files, and the structures of fully austenitic (conventional superelastic), austenite treated, and fully R-phased were used. The mechanical responses were evaluated under flexion and torsion loading conditions described by ISO 3630-1 specification. According to the results, the design of the X1 file exhibit higher flexibility in comparison to the S2 model. Under torsional loads, S2 showed higher stiffness. The structures of fully austenitic showed the least flexibility under flexion and the highest torsional stiffness. The stress levels reached for the austenitic condition were uppermost. The treated condition that resulted in a fully R-phase file usually presented a higher level of flexibility with lower stress levels, indicating a longer life in fatigue when compared to the other treatments.

Resumo em Inglês:

The mechanical behavior of metastable β Ti alloys can be controlled through heat treatments. Thus, the relationship between the precipitation of α phase and the mechanical properties of these alloys is of special interest. In this work, the microstructure evolution of Ti-30Nb-3Fe alloy during aging heat treatments was evaluated using optical microscopy, scanning electron microscopy and X-ray diffraction. Moreover, Vickers hardness and elastic modulus were measured as a function of aging time. Finally, the ultimate strength and ductility of the alloy aged at 500 °C was assessed by tensile tests. In comparison to a Ti-30Nb alloy, the addition of Fe lowered the β-transus temperature, decreased the martensite start temperature to a value below room temperature, increased the precipitation temperature and reduced the dissolution temperature of ω phase, and lastly, decreased the α phase precipitation temperature. Low heating rates enabled isothermal ω phase precipitation and growth, providing favorable conditions for α phase precipitation and increasing the amount of α phase precipitates. Compared to the solution heat-treated and water-quenched condition, aging heat-treated Ti-30Nb-3Fe alloy presented higher Vickers hardness and mechanical strength, without significant loss of ductility.

Resumo em Inglês:

This work presents the investigation, at room temperature, of Zn2TiO4samples containing Ni2+ ions as substitutional impurities. Samples with molecular formula Zn2(1-x)Ni2xTiO4, where x = 0.00, 0.0007, 0.001, 0.0013, 0.002 and 0.003, in which Zn2+ ions were replaced by Ni2+ ions, were prepared through solid-state method, crystalline data were obtained by X-ray diffraction, the elemental composition was determined by X-ray fluorescence and the optical properties were investigated through photoluminescence and photoacoustic techniques. The photoluminescence spectra showed broadbands from 640 nm to 800 nm. The emission of the Zn2(1-x)Ni2xTiO4 samples was assigned to the overlapping of the Ni2+and the Zn2TiO4 emission. The most intense photoluminescence signal was obtained with excitation radiation at a wavelength of 360 nm for the sample with x = 0.001. The photoacoustic spectra showed absorption bands characteristic of semiconductor materials due to the host Zn2TiO4. The energy bandgap of the Zn2(1-x)Ni2xTiO4was obtained from photoacoustic absorption spectra.

Resumo em Inglês:

Abstract Copolymers based on glycidyl methacrylate (GMA) are considered attractive as sorbents because the epoxy groups can be easily converted into other groups. Studies involving the influence of the synthesis parameters on the morphological characteristics of these copolymers are scarce. This work investigates the synthesis of copolymers of poly(GMA-co-EGDMA) with different porosity degrees obtained by varying the synthesis parameters. GMA-EGDMA copolymers were synthesized by suspension polymerization employing varied conditions and characterized by measuring apparent density, surface area and pore volume distribution, optical and scanning electron microcopies, FT-IR, thermogravimetry and titration of epoxide rings. The copolymer with highest surface area and pore volume (260.4 m2/g and 0.5 cm3/g) was prepared employing cyclohexane as diluent, 80% EGDMA in monomeric composition and 100% of dilution degree. There was a relation between the epoxide content of the copolymers determined by titration and the residue content formed in the first decomposition stage.

Resumo em Inglês:

Abstract In the current work, the microstructure, mechanical properties and machinability of Ti15SnxCu alloys (x = 0 to 2 wt. %) were investigated. The alloy was prepared by the vacuum arc remelting and casting route and then thermally processed by solutionizing at 1000 °C for 2 hours, followed by water quenching. By controlling the heat-treated condition and Cu content, the highest bending strength and modulus were obtained from three-point bending testing. The increases were mainly caused by the strengthening effects of the formation of crystallites with fine grain size and nano-Ti2Cu precipitate phase. In addition, nano-Ti2Cu precipitation was caused by crack initiation and propagation, which reduced the ductility and improved the machinability of Ti15Sn2Cu alloy.

Resumo em Inglês:

Abstract Materials such as magnesium phosphate cement (MPC) have attracted significant attention of researchers, therefore, understanding the effects of dosage parameters, such as water content and MgO/NH4H2PO4 ratio on phase formation is essential for obtaining cementitious matrices with improved performance. In the present work MgO was sintered at 900 °C and 1110 °C in a conventional oven, and the effect of water concentration and MgO/NH4H2PO4 (or ADP) ratio on the properties of MPC was evaluated in terms of phase formation by X-ray diffraction, pore size distribution, mechanical properties, and microstructure. For less-reactive MgO (calcined at 1100 °C) with a high MgO/ADP ratio, increased water content did not cause additional solubilization of ADP or formation of more hydrated phases, although the cement porosity increased. Compositions with more reactive MgO (calcined up to 900 °C) formed dittmarite (NH4MgPO4.H2O) independent of water content. Higher water content and MgO calcination temperature were associated with increased MPC setting time and decreased mechanical strength due to higher porosity.

Resumo em Inglês:

Abstract Previous studies showed the formation of new phases affecting the electrical properties of LSC thin films deposited on stainless steel substrates, which are commonly tested for ITSOFC and SOEC interconnects. A 4.3 μm thick La0.6Sr0.4CoO3 coating was deposited on AISI430 steel by spray pyrolysis, followed by heat treatment (800°C/2h) and an oxidation in air (800°C/96h). The La0.6Sr0.4CoO3 phase interacted with the metallic substrate and formed SrCrO4, causing degradation of the perovskite into La0.9Sr0.1CoO3. An EDS mapping showed Sr and Cr enrichment in the coating/substrate interface. TG analysis indicated a lower mass gain for the coated substrate. The total ASR at 800°C of the interconnect before and after oxidation was 3.23 Ω.cm2 and 3.98 Ω.cm2, respectively. The Ea underwent very small variation, remaining around 0.24 eV (T≤300°C) and 0.65 eV (T≥400°C). The reaction of Cr from the substrate and Sr from LSC seems to have impaired the performance of the interconnect.

Resumo em Inglês:

AZO thin films (around 200 nm thick) were grown on polyethylene terephthalate (PET) at room temperature. The plasma was activated using a 13.56 MHz (RF) or a 15 kHz pulsed (PMS) source at a power of 60 W. Optical reflection and transmittance were measured using a UV-Vis-NIR spectrometer over the wavelengths from 190 nm to 2500 nm. All samples show average transmittances greater than 83% in the visible region. The electrical resistivity was measured by the linear four-point probe method to be around 0.001 Ωcm for 200 nm-thick AZO films grown by PMS. XRD results indicated that the films had a hexagonal wurtzite structure and were preferentially oriented in the (002) plane. The surface morphology of the AZO thin films was characterized using Scanning Electron Microscopy (SEM); film chemical composition was studied using Energy Dispersive X-ray Spectroscopy (EDS). For this, an EDS coupled to the Scanning Electron Microscope was used. Only for films grown by PMS were no cracks observed.

Resumo em Inglês:

Abstract Duplex and super duplex stainless steels have high corrosion resistance, excellent mechanical properties, and high impact strength. Such characteristics make these steels able to operate in various segments of the industry, especially in aggressive environments. These alloys have higher strength than austenitic and ferritic stainless steels and their operation is generally restricted to temperatures lower than 300 °C. Most steels and alloys only exhibit elasto-viscoplastic behavior at temperatures higher than 1/3 of the absolute melting temperature. The objective of this work was to make an experimental study showing that the duplex and superduplex steels present a rate-dependent behavior even at room temperature (around 25 °C). Two different alloys: duplex stainless steel UNS 31803F51 and super duplex UNS S32760GRF55 were used in the study. Simple models were proposed to describe how the rate-dependent portion of the stress (called at this paper “the viscous term”) depends on the strain rate. A simple procedure to identify experimentally all material constants that appear in the theory is presented. The experimental results are in very good agreement with the model predictions.

Resumo em Inglês:

This study reports the structural properties of zinc oxide thin films co-doped with aluminum and nitrogen (ZnO:Al-N) grown by RF magnetron sputtering from an AZO (ZnO with 2 wt% Al2O3) target under nitrogen (N2) atmosphere at room temperature (RT). Nitrogen partial pressures of 0.00, 0.10, 0.25 and 1.00 mTorr were used. The film thickness was around 270 nm. Ultraviolet-Vis-NIR transmittance (T) spectra of the films revealed T values of 80 to 85% in the 400 to 700 nm wavelength range. XRD results indicated that the films had a hexagonal wurtzite structure and were preferentially oriented in the (002) plane. Analyses by EDS indicated that the N atoms tend to be incorporated into the ZnO matrix at the expense of oxygen atoms. The ideal [N]/[Al] was obtained at a N2 partial pressure of 0.25 mTorr, producing a p-type film. For a [N]/[Al] of 1.53, the film also exhibited p-type conduction with an electrical resistivity of 31.92 Ω cm, mobility of 18.65 cm2/V s and carrier density of 1.22 x 1016 cm-3. The low carrier density is attributed to the energetically favorable formation of inactive nitrogen phases instead of acceptor-receiver-acceptor complexes, even at the ideal [N]/[Al].

Resumo em Inglês:

In this work, influence of machining parameters of the electro discharge machining (EDM) and Abrasive-water jet machining (AWJM) processes on the material removal rate, tool wear rate and surface roughness of the composites were investigated. Titanium nitride and tantalum carbide particles reinforced vitallium composite material was synthesized by stir casting method. The machining characteristics were analyzed through Taguchi and ANOVA methods. The Taguchi optimization technique was used to find the optimal level of parameters while the percentage of contribution for each input parameter on the responses was computed by ANOVA. Scanning electron microscope (SEM) was employed to examine the surface morphology.

Resumo em Inglês:

UNS S31603 stainless steel (SS) substrates were covered by reactive magnetron-sputtering with protective SS coatings of the same steel specification. A mechanical characterization study (through nano-, micro- and macro-hardness tests) of samples obtained under two different sputtering conditions and varying the N2 gas flow rate was carried out. This contribution aimed at appraising the effects of varying the nitrogen flow rate on hardness, elastic modulus, and susceptibility to indentation-induced crack formation of the coated SSs. Nitrogen-free samples displayed body-centered cubic (BCC) films with 9.0-9.4 GPa hardness and 203-206 GPa elastic modulus, while their susceptibility to indentation-induced cracking varied between superior and moderated among the two sets of sputtering conditions studied. Samples alloyed with 4-6 N at-% displayed a predominantly face-centered cubic (FCC) structure, 9.4 GPa hardness, 196-218 GPa elastic modulus, and superior resistance to crack formation. Samples with 11.5-22.0 N at-% were fully composed of the FCC structure, displayed 12.4-15.2 GPa hardness, 188-193 GPa elastic modulus, and moderated resistance to indentation-induced crack formation. Samples with 47.0 N at-% displayed FCC compound nitride structure, for which hardness and elastic modulus were 8.1 GPa and 139 GPa, respectively. These samples displayed low resistance to crack formation.