Resumo em Inglês:

Abstract In this paper a new modified processing route has been proposed for producing long cylindrical cups from 12 mm thick circular blanks of AISI 1020 steel (Aluminium (Al) -killed). In this route, flat blanks were made to preformed shape by stamping operation, followed by multistage deep drawing processes(without blank-holder and with inter-stage stress relief annealing) to increase cup depth. Wall ironing was also purposefully included in each draw step to reduce wall thickness and earing tendency on cup edges. Thus, evolution of wall thickness distribution, Drawability and Ironability, punch force history, and strain distribution profiles on outer cup surfaces were obtained as the effects of interaction between processes, tools and material. The overall draw stages showed: LDR 2.06; overall draw reduction >50% with a drawing efficiency ~72%; LIR 3.55; overall ironing reduction >70% with an ironing efficiency ~68%, which were achieved in the experimental works.

Resumo em Inglês:

Abstract In this paper, a new way for γ-alumina synthesis was proposed, the raw material being aluminum powders obtained by high-energy milling of aluminum cans. This seems a good option for this metal recycling and energy saving, as well as hydrogen production. The materials were prepared by precipitation techniques, in which aluminum powders reacted with hydrochloric acid, giving aluminum chloride, which was subsequently transformed into aluminum hydroxide by reaction with ammonium hydroxide or sodium hydroxide as precipitant agents, and finally into γ-alumina by calcination. Results showed that the used preparation methods gave a γ-alumina structure, confirmed by XRD, with surface areas values (174 and 204 m2 g-1) close to those of a commercial γ-alumina Cyanamid Ketjen (180 m2 g-1) or an alumina prepared by a typical precipitation route (203 m2 g-1). Using sodium hydroxide as precipitant agent turned out to be more ecologically compatible since it did not release harmful environmental compounds.

Resumo em Inglês:

Abstract The present work reports the synthesis of nanocomposite of polypyrrole with [Fe(CN)3(dien)].H2O photoadduct via in-situ oxidative chemical polymerisation. Photoadduct was synthesised by irradiating an equimolar mixture of K3[Fe(CN)6] and diethylenetriamine (dien) using Osram photo lamp. The successful synthesis of photoadduct was proved by Elemental analysis, UV-Vis and FTIR spectra. Nanocomposite of photoadduct with PPY was then prepared by oxidative chemical polymerization using FeCl3 as oxidant. The successful synthesis of the nanocomposite was confirmed from FTIR, XRD and SEM. The nanocomposite showed significant increase in thermal stability, dielectric constant and ac-conductivity as compared to pure polypyrrole. The photocatalytic activity of the materials was also studied against the methyl orange (MO) dye under UV-Vis light and nanocomposite showed efficient photocatalytic activity (91 % degradation after 2 hrs) than pure PPY which showed only 24% degradation of dye after 2 hrs. Thus as synthesised nanocomposite can be effectively utilised for the removal of organic dyes.

Resumo em Inglês:

Abstract CuI crystalline thin films were produced on substrates (commercial glass) using chemical extraction method in different chemical bath media. In this study, their structural, optical and electrical properties were analyzed. Transmittance, absorption, optical band gap and refractive index of the films were examined by UV/VIS spectrum. XRD data showed that the film has a hexagonal structure for CuI. Surface and elemental (in terms of ratio) analysis of the films were performed via SEM and EDX analysis. The highest average grain size of CuI was observed for the film produced in aqueous media whereas the lowest average grain size was seen in chloroform bath. The curve formed by the number of crystallites per unit area (N) is different than the curves of dislocation density and average grain size. Number of crystallites per unit area has reached its maximum value in CCl4 bath, but it has been decreased in chloroform bath. In addition, film thickness has varied between 1232 nm and 3624 nm according to the solvent of bath.

Resumo em Inglês:

Abstract The present research work explores the room temperature gas sensing ability of hybrid nanocomposites of metal sulphide nanoparticles with polypyrrole (PPy) matrix. Sonochemically synthesized both silver sulphide (Ag2S) and cadmium sulphide (CdS) nanoparticles were mixed in varying ratios with PPy matrix by in-situ oxidative polymerization route. The resulting PPy/(Ag2S:CdS) hybrid nanocomposites were analyzed by characterizing them using FTIR and UV-Visible spectroscopy, XRD, SEM, four-probe conductivity method and gas sensing ability by two-probe gas sensing setup. The current-voltage (I-V) characteristics of the PPy hybrid nanocomposites revealed their semiconducting nature with an electrical conductivity in the range of 10−4 to 10−3 S/cm. As compared to pure PPy, their hybrid PPy/(Ag2S:CdS) nanocomposites showed an enhancement in sensitivity towards ammonia gas detection. The results clearly indicated a synergistic effect between the Ag2S:CdS nanoparticles and the PPy matrix.

Resumo em Inglês:

Abstract Duplex stainless steels have a structure normally composed of austenite and ferrite in approximately equal proportions. In order to attain control of its fabrication processes and performance, it is important to understand its microstructural evolution, due to the formation of intermetallic phases such as sigma (σ) and chi (χ), which may cause a severe deterioration of mechanical properties. In the present study, the evolution of sigma phase during heat treatments at temperatures in which intermetallic phases can be formed (800ºC-900°C) was studied using magnetic analyses on a SAF2205 (DIN 1.4462/UNS S31803) steel. A significant reduction of the intensity of Magnetic Barkhausen Noise (MBN) was observed with the increase of heat treatment time, indicating a decrease in the quantity of ferromagnetic phases. For 24-hour-long treatments, the Barkhausen Noise signal is almost completely enclosed by the background noise, indicating the existence of a very small volume fraction of ferrite. If proper calibration samples are to be produced, this technique may be a viable method for non-destructive evaluation of field components working under thermal conditions that may cause the formation of intermetallic phases.

Resumo em Inglês:

Abstract The nano/microstructures with highly porous surface area have attracted tremendous attention, particularly the synthesis and tailoring of porous and hollow materials of high performance. In this paper, an easy method of cost-effective synthesis of hollow ceramic fiber membranes based on Hydroxyapatite, TiO2 and ZrO2 stabilized with Yttrium, is proposed by a single chemical route (polymeric precursor method) and a bio-template route (easy to degrade in thermal conditions). This article reports also the ZrTiO4 nanowires synthesis on a silicon (100) wafer in a single step deposition/thermal treatment. Template-directed membrane synthesis strategy was associated to the polymeric precursor route and spin-coating deposition technique. In this method, ZrTiO4 nanowire ceramic were synthesized by spin-coating thermal treatment technique using polycarbonate membrane as a template. According to the results, after heat-treatment by the template removal, the ZrTiO4 nanowire consists of uniformly deposited crystalline and porous nanoparticles that exhibited a higher surface area and a higher porosity. The polycrystalline nanowires were obtained at by thermal treatment with diameter in the range of 60-100 nm. Photoluminescence spectra were collected for fiber at room temperature. These characterizations demonstrate the morphology of structures formed, showing its hollow and porous conformation, suitable applications to advanced reinforced or device component material.

Resumo em Inglês:

In this paper are presented the results of the calculation of thermodynamic properties in liquid state for ternary Cu-Ga-Ni alloys using the newest version of general solution model. Calculation was carried out in temperature interval 1473-2073 K, along 3 cross sections from corner of each metal, with ratios between two other metals 1:3, 1:1 and 3:1. Partial and integral molar thermodynamic properties in liquid phase for the Cu-Ga-Ni ternary system are determined, presented and discussed. Calculated data is compared with data available from literature and good agreement between these two sets of data was observed. Additionally, isothermal section of phase diagram at 298 K is calculated using Thermo-Calc software and presence of eleven different phases is detected. Presented thermodynamic data for the Cu-Ga-Ni alloys could be useful for the further assessment of this system and its phase diagram as well as for completing thermodynamic description of these alloys.

Resumo em Inglês:

Abstract Machining procedures of welding deposits are usual and result on cold work hardened surfaces. The cold work effect on cavitation erosion of an austenitic stainless steel surface is assessed. FeCrMnSiB coatings were processed by PTA on AISI 304 plates. Specimens were grouped as the cold work deformed surface (CWHS) and the undeformed polished surface (UPS) specimens. Top surface and transverse section of coatings were analysed for slip lines and hardness changes by light microscopy and Vickers microhardness measurements. Ultrasonic cavitation tests were conducted in accordance to ASTM G32-10. CWHS specimens exhibited slip lines and hardened surfaces while UPS specimens did not show traces of slip lines and had insignificant changes on microhardness. Cold work prior to cavitation indirectly increased the nominal incubation time and reduced the maximum erosion rate. Cold work increases the duration of the acceleration period postponing the onset of the maximum erosion rate and enhancing cavitation resistance.

Resumo em Inglês:

Abstract The crystallographic texture developed during cold rolling and subsequent annealing of interstitial free sheet steels aims to increase conformability. For this, it is necessary to obtain partial α-fiber and continuous and homogeneous γ-fiber texture components. In this work, the influence of symmetric (SR) and asymmetric (AR) cold rolling on crystallographic texture and mechanical properties of an interstitial free steel (IF) was investigated. Symmetric cold rolling yields α- and γ-fibers, which are enhanced as deformation increases. Moreover, α-fiber weakening occurs due to recrystallizations, improving formability. The same fibers are produced by asymmetric cold rolling, but in this case, the γ-fiber is slightly shifted in psi, which is one of Euler angles second ROE's notation1,2, and more homogeneous than in symmetric rolling. The best mechanical properties were achieved by asymmetric cold rolling/annealed with about 80% deformation.

Resumo em Inglês:

Abstract To modify the surface structure of AISI 1005 steel and its properties without any dimensional loss, different plasma surface treatments were performed at low temperatures (500 ºC) in this study. The samples were subjected to single plasma treatments including: nitriding (N5% and N3%), carburizing (CE) and ferritic nitrocarburizing (NC) and to duplex treatments of nitriding followed by carburizing (N5%+CE and N3%+CE) and ferritic nitrocarburizing followed by carburizing (NC+CE). The gas mixture used for these treatments was varied as follows: nitriding (5%N2+95%H2 and 3%N2+97%H2), carburizing (5%CH4+95%H2) and ferritic nitrocarburizing (5%N2+1.5%CH4+93.5%H2). A microstructural characterization of the samples was carried out using optical and scanning electron microscopy in addition to XRD analysis. Microhardness testing was also performed. The XRD analysis showed a stabilization of the outermost cementite layer for all of the carburizing treatments. The results show that a greater hardness increase was achieved for the nitriding treatment as well as a more regular compound layer. However, a greater depth of hardening was obtained in samples with NC+CE and N5%+CE, which extended to the hardened depth to 800 µm.

Resumo em Inglês:

Abstract In this work, cobalt and zinc-doped Ce0.8Gd0.2O1.9 samples were prepared starting from a commercial nanopowder and compared to the undoped material. The powder samples were pressed and afterwards sintered by a two-step procedure, before characterization by X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Impedance Spectroscopy (IS) in air. Cobalt or zinc additions are effective as sintering aid, allowing peak sintering temperatures around 1000°C to reach densifications above of 93% of theoretical density, showing no evidence for the presence of secondary phases. The total conductivity at 800 °C of pressed Zn-doped samples (6.7x10-2 S/cm) and Co-doped samples (7.5x10-2 S/cm) is similar for undoped samples (7.2x10-2 S/cm) showing that Zn and Co has a positive effect on densification without compromising the electrical conductivity.

Resumo em Inglês:

Abstract In this work, compositions containing transparent glass bottles and banana leaves (desiccated and crushed), with different mass fractions (30-50%), were prepared for obtaining cellular materials for thermal insulation purposes. The formulated and prepared compositions were uniaxially pressed (10 MPa) and the compact powders fired between 700 and 850°C for 30 min in order to investigate the effect of the banana leaves on the formation of pores and on the thermal and mechanical properties of the processed glass foams. The results indicated that the obtained glass foams with porosities between 58.5 and 87.5%, compressive strength ranging between 1.17 and 3.50 MPa and thermal conductivity ranging between 0.06 and 0.15 W/mK, are potential candidates to work as thermal insulators with appropriate properties for a specific application.

Resumo em Inglês:

In this study we prepared hydrogels based on 2-hydroxyethyl methacrylate (HEMA): PHEMA homopolymer and two terpolymers of HEMA, itaconic acid (IA) and two poly(alkylene glycol) (meth) acrylates (PAGM): poly(ethylene glycol)6 acrylate (P(HEMA/IA/PAGM1)) and poly(propylene glycol)5 methacrylate (P(HEMA/IA/PAGM2)). Hydrogels were synthesized by gamma-irradiated radical polymerization and subjected to swelling measurements and genotoxicity evaluation. Swelling studies confirmed that these hydrogels deserve consideration as biomaterials due to their ability to swell in phosphate buffer but maintaining physical integrity for a prolonged contact time after equilibrium state has been reached. Comet assay showed certain genotoxic effect following cell exposure to extracts of hydrogels, which was dependent on the concentration of extracts, chemical composition of hydrogels and the degree of crosslinking. The influence of concentration on genotoxicity was the most pronounced. The synthesis of these novel HEMA-based hydrogels should be optimized so as to reduce their toxicity and enable the use in clinical practice.

Resumo em Inglês:

Abstract Core/shell structures of carbon-based materials/ metal oxide have been considered as potential candidates for electrochemical devices due to their improved pseudocapacitance/electrical double layer capacitance and high conductivity/ superior surface area. The development of multiple core-shell structures of MWCNT@MnO2@PPy was analyzed as a standard procedure for mass production of supercapacitor electrodes. The relative concentration of carbon nanotubes in the composite was varied to optimize the double layer capacitance contribution in overall response of device. Resulting structures presented capacitance in order of 272.7 Fg-1 and reasonable cycling performance.

Resumo em Inglês:

Hydrogen embrittlement is a phenomenon that affects the performance of steel used for oil and gas pipelines. This paper presents a study of the effect of hydrogenation on the residual stresses of an API 5L X65 steel pipe. Residual stresses were analyzed by X-ray diffraction technique using the sin2Ψ method. The hydrogenation of base metal and welded joint specimens was performed by electrochemical tests in a simulated soil solution NS4. Results show that the hydrogenation led to significant changes in residual stress configuration and in the mechanical properties of steel. The hydrogenation increased the magnitude of the longitudinal residual stress of base metal and fusion zone, without changing the tensile/compressive nature. On the other hand, the hydrogenation increased the intensity of the tangential stress of base metal, and changed from compressive to tensile the residual stress of the fusion zone. The microstructural characterization by optical and scanning electron microscopy was used to complement this study.

Resumo em Inglês:

Titanium nitride films were deposited on silicon by plasma discharge in cathodic cage with holes and without holes on the sides. Each film was deposited with a pressure of 253 Pa, treatment time of 2 h, and at diverse conditions of temperature and gas flow of N2 and H2. The electrochemical polarization and electrochemical impedance techniques were used to understand the effect on the electrochemical properties of these films in relation to the presence or absence of holes on the sides of the cathodic cage and to investigate the electrochemical behavior of the films formed, which presented as both capacitive and resistive for the conditionsanalyzed.

Resumo em Inglês:

The ADN420 ferritic steel (A615 steel Grade 60 [420]), used as reinforcing bars (rebar) in concrete, shows the so called ductile to brittle transition. Room temperature is located on the lower third region of the transition zone. In this work, the fracture toughness of this steel working at room temperature was studied statistically. For such a purpose, 125 compact test specimens were machined from commercial bars and tested at room temperature to determine the Jc and KJc critical fracture toughness values. Several continuous probability functions with threshold parameter were adjusted to the J and K datasets.

Resumo em Inglês:

The aim of this work was to study the structural characteristics of commercially available bone graft substitute (BGS) ceramic cements. In particular, the microstructure of two calcium sulfate cements was investigated. For this purpose, nitrogen and mercury porosimetry, x-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements have been carried out. Mercury intrusion porosimetry results revealed that the structural characteristics of the two samples varied significantly. These structural differences can be justified when compared with their compression and bending strength properties. As a result, a proper understanding of microstructure of BGS materials is crucial in the search of what is optimal for bone regeneration.

Resumo em Inglês:

Chitosan/montmorillonite (CTS-MMT) composite beads were used as adsorbents for the removal of silver ion (Ag+) from aqueous solution. Equilibrium adsorption was achieved within 150 min at 3% MMT of chitosan solution. The optimum pH value for Ag+ removal was found to be 6-7. The maximum adsorbent dosage for Ag+ removal was 5 g/L. Under above maximum conditions the Ag+ removal was 95.7%. The maximum adsorption capacities of CTS and CTS-MMT composite beads as obtained from Langmuir isotherm were found to be 38.46 and 43.48 mg/g, respectively. The adsorption kinetic agrees well with the pseudo second order model. The Ag+ desorption of CTS-MMT composite bead was 17.39% at pH=4. SEM/EDX images confirm that after adsorption the Ag+ were dispersed onto the composite bead surface. The adsorption and desorption experiment demonstrated that the CTS-MMT composite beads can be used as an effective adsorbents for removal of Ag+ from aqueous solution.

Resumo em Inglês:

Alloys containing Me-Si-B (Me - Refractory Metal) are of great interest for high temperature structural applications and accurate knowledge of its low order systems (binaries and ternaries) is important to predict the phase relations in the multicomponent alloys. Recent reevaluations of binaries containing Me-Si found out that the accuracy of the description of this type of systems could be improved. Knowing this, a reevaluation of the invariant reactions in the V-Si system via microstructural characterization of as-cast alloys is presented. Alloys of key compositions were prepared by arc melting pure V (min. 99.75%) and Si (min. 99.998%) and characterized via scanning electron microscopy (SEM) using back-scattered electron (BSE) mode, energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results of this study confirmed the solid phases, the nature of the invariant reactions and determined new compositions for the liquid participating in certain invariant reactions.

Resumo em Inglês:

In steel mills that operate with electric arc furnaces (EAF), it is interesting to ensure greater stability to the electric arc to aim at less distortion in the electrical system, with consequent reduction in electric power consumption. The slag foaming increases electric arc stability by reducing the total harmonic distortion (THD) between EAF phases. In this study, information about the chemical composition of the slag and electrical parameters of an EAF were collected. With the composition data, it was possible to determine the FeO and MgO content and basicity of the foamy slag which caused a reduction in THD and in electric power consumption. The effective viscosity of foaming slag was calculated and an increase in the effective viscosity provided a decrease in THD. A reduction of THD showed a decrease in the consumption of electric power in the EAF refining stage.

Resumo em Inglês:

Ti‒50.13Ni and Ti‒49.62Ni (at.%) shape memory alloy ribbons were fabricated by melt-spinning method at different circumferential wheel velocities. The effects of wheel velocity, chemical composition and heat treatments on microstructure and Transformation temperature were investigated. Differences in wheel velocity led to differences in cooling rate and sample dimension, as well as in phase transformation temperatures. Two heat treatment conditions were studied, 350°C for 1h and 350°C for 5h. In the samples produced at high wheel velocity and heat-treated at 350°C for 5h, nanosized Ti-rich precipitates were observed in both chemical compositions. Cross-sectional microstructure was studied by optical microscopy; SEM was used to study the nanometric grains and nano precipitation. The transformation temperatures were analyzed by DSC.

Resumo em Inglês:

In this study, a tailored die quenching experimental method using low closing pressures and an aluminum flat die was developed in order to evaluate the effects of the gap size on the cooling rate in the hot stamping process of a 22MnB5 steel grade. Initially, the necking behavior in hot stamping was investigated by deforming the specimens to different strain levels and subjecting them to quenching in order to assess this effect on the gap profile formed between the die surface and the sample. Next, a controlled gap was promoted in the central region of the aluminum cooler using aluminum spacers (simulating the gap) with different thickness (0.06/0.15/0.40/0.70mm). Then, its effects on the cooling rate and on the hardness after quenching were evaluated. The results showed that the cooling rate is very susceptible to gap size, that the ideal situation occurred when there was no gap, good heat transfer and higher average cooling rates of 120ºC/s were achieved, and that when the gap was wider than 0.20mm the average cooling rates were lower than 20ºC/s, consequently below the critical 22MnB5 steel cooling for quenching, which is 28ºC/s.

Resumo em Inglês:

High-pressure torsion was used to process grade 2 titanium to 10 turns using different pressures up to a maximum of 8 GPa. X ray diffraction showed that the as-received material and the material processed at pressures of 2 GPa and 4 GPa were single phase but the material processed at 8 GPa contained both the h.c.p. and the simple hexagonal ω-phase. Nanoindentation was used to determine the mechanical behavior and the results show a pronounced increase in hardness due both to the severe plastic deformation processing and to the phase transformation at the highest pressure. A maximum hardness of ~4.7 GPa was attained.

Resumo em Inglês:

NiFe2O4 nanosheets have been synthesized via a simple surfactant-assisted solution route, which are confirmed by X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. The NiFe2O4 sample exhibits the sheet-like structure, with width varying from 200 to 800 nm and thickness ranging from 20 to 60 nm. The electromagnetic properties of NiFe2O4 nanosheets-paraffin composites have been deeply investigated. The multiple dielectric relaxation loss in NiFe2O4 nanosheets is attributed to the size distribution and morphology of the NiFe2O4 nanosheets. The magnetic loss in the present system is caused mainly by the natural resonance. An absorber with a thickness of 4.3 mm exhibits an optimal reflection loss (RL) value of -47.1 dB at 7.67 GHz. RL values exceeding -20 dB in the 2.68-17.96 GHz range are obtained by choosing an appropriate absorption-layer thickness between 1.9 and 10 mm. Not only the RL peak frequency but also the number of the peaks can be well explained by the quarter-wavelength cancellation model.

Resumo em Inglês:

We present a study of the controlled synthesis and optical properties of single-crystals Gd(OH)3, GdOOH and Gd2O3 nanorods. In this work, Gd(OH)3 nanorods were synthesized by a simple and fast microwave-assisted hydrothermal method. This process combined with the thermal decomposition oxidation of Gd(OH)3 nanorods as precursors enabled the preparation of single-crystalline GdOOH and Gd2O3 structures with well-defined morphology at low temperatures. The crystal structure dependence on the optical properties was investigated. We observed a green shift effect on the photoluminescence (PL) emission spectra from Gd(OH)3 to Gd2O3 nanorods, which can be attributed to different types of surface defects, as well as intrinsic properties that contribute significantly to the modified PL behavior.

Resumo em Inglês:

Aluminum is often added to electrical steels since this element causes improvement of the magnetic properties. However the addition of aluminum is usually limited to 0.30 wt%1. Therefore, this work aimed at evaluating the influence of higher levels of aluminum in the magnetic properties of semi-processed steels. To accomplish this, four types of steel were produced in laboratory with different aluminum contents (0.10, 0.30, 0.60 and 1.0 wt%). Carbon, manganese and silicon concentrations were kept constant. It was observed that an increased aluminum content caused reduction of the magnetic core loss, especially of the eddy current component. However, the magnetic permeability virtually wasn't influenced by aluminum concentration.

Resumo em Inglês:

Pure and Mn2+ doped poly(vinyl chloride) (PVC) polymer films were prepared using the solution cast technique. The prepared samples have been characterized by X-ray diffraction (XRD), UV-Vis Spectroscopy (UV-Vis), Fourier transform infrared (FTIR) Spectroscopy, Thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), Electron Paramagnetic Resonance (EPR) and Scanning Electron Microscopy (SEM) studies. TGA/DSC analysis reveals that the sample is thermally stable upto 350 0C. The morphology of the polymer films was studied by SEM. The optical absorbance of the polymer films was measured in the 200-900 nm wavelength range. The absorption edge, direct band gap and indirect band gap have been evaluated. The FTIR spectrum exhibits several bands characteristics of stretching and bending vibrations of C - Cl, C - H, C = C and O - H groups. The EPR Spectra at room temperature were used to calculate the number of spins and paramagnetic susceptibility as a function of dopant concentration. All the Mn2+ doped PVC samples exhibit a signal centred at geff = 1.9. The observed variation in the EPR signal intensity is due to the variation in the dopant concentration. The complexation of Mn2+ ion with the polymer was confirmed by XRD studies.

Resumo em Inglês:

The API 5L X70 steel is used in high-pressure gas transmission pipelines. Because of this, knowledge of presence of residual stress and their magnitude is important to assess the material integrity in service. For the pipeline manufacturing, tubes need to be curved which is often made using the hot induction bending process. This process can introduce different residual stress depending of tube position. For this research, in order to evaluate the residual stress, was used an API 5L X70 tube that was previously curved by hot induction process. Samples were taken from the extrados, intrados, neutral line and straight section of the curved tube. Residual stresses were studied by two conventional methods: X-Ray Diffraction (XRD) and Hole-Drilling, which are destructive and non-destructive methods, respectively, in order to assess their qualitative responses. Each of these methods presents particular methodologies in sample preparation and material analysis, but also they differ in factors such time consumption and cost of the analysis. The qualitative responses obtained by the two different methods were comparable and satisfactory and pointed out the existence of a compressive residual stress state in steel pipe.

Resumo em Inglês:

When multifunctional surface engineering processes that combine purpose-oriented phases are applied to soft substrates, a combination of high wear resistance, high load support and low coefficients of friction can be achieved. In this study, the effects of different nitrided layers on the tribological behaviour of a diamond-like carbon (DLC) film deposited on a SAE 1040 steel were investigated. The nitriding was carried out under different temperatures and gas mixtures to create three distinct nitrided layers: two compound layers with predominant ε and γ' phases and a diffusion layer. All of the surfaces were then coated with DLC deposited via plasma-enhanced chemical vapour deposition (PECVD). The tribological tests indicated that the best performance was achieved for a specific combination of hardness, surface roughness and nitride type. The best load-bearing capacity between the DLC coating and the soft substrate was achieved when the nitrided layer was primarily a diffusion layer.

Resumo em Inglês:

Aluminum-15 wt. % zircon metal matrix composite was fabricated using spark plasma sintering method at the temperature of 450°C and holding time of 4 min. The bending strength of 284±21 MPa and microhardness of 171±14 Vickers were determined for produced composite. XRD investigations proved that almost no decomposition of zircon particles as reinforcement occurred. SEM studies revealed the homogenous dispersion of reinforcement particles in the aluminum matrix.

Resumo em Inglês:

The aim of this work is evaluate the influence of welding conditions on abrasive wear resistance in coating of Fe-Cr-C. The metal base used in this investigation was the steel SAE 1020 and as welded metal the selfshilded tubular wires of Fe-Cr-C with 1.6 mm of diameter. The welding parameter such as amperage, voltage, welding speed, wire feed speed and the distance between the point and samples were kept constant by varying the electrode inclination and the number of layers deposited. These resulted in four different weld conditions: pulling and pushing the weld pool and hardfacing formed with 1 end 2 layers. Their influences on dilution, microhardness and microstructure were evaluated and correlated with the abrasive wear according to the standard tests methods for abrasion measurements through the usage of dry sand/rubber wheel apparatus, ASTM G-65-04. The results showed that the wear resistance of the four different conditions was affected by dilution, microstructure morphology and carbide volume fraction. The best conditions for hardfacing deposition were for pushing the torch and two layers added.

Resumo em Inglês:

We report on the preparation and performance enhancement of n-type low-voltage organic field effect transistors (FETs) based on cross-linked poly(vinyl alcohol) (cr-PVA) as gate dielectric and C60 fullerene as channel semiconductor. Transistors were prepared using bottom-gate top-contact geometry and exhibited field-effect mobility (µFET) of 0.18 cm2V-1s-1. Treatment of the gate dielectric surface with an anionic surfactant, sodium dodecyl sulfate (SDS), passivates the positively charged defects present on the surface of cr-PVA, hence resulting in overall transistor performance improvement with an increase in µFET to 1.05 cm2V-1s-1 and additional significant improvements in dielectric capacitance, transistor on/off current ratio and transconductance.

Resumo em Inglês:

This research used the "cathodic cage (CC)" technique for TiO2 film deposition on duplex stainless steel substrate. This technique uses a multiple hollow cathode effect. Duplex stainless steel substrates were treated at temperatures of 300°C, 350°C and 400°C, giving a temperature value ratio (Ts/Tm) of 0.27 to 0.31 (Ts being the substrate temperature and Tm the melting temperature of the deposited material). Treatment times of 1, 2 and 4 hours were administered and polycrystalline TiO2 films were obtained. The films were analyzed by optical microscopy (OM), X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). During analysis, the formation of uniform films and the possibility of controlling the TiO2 phase were observed. It was also shown that with longer treatment times and higher temperatures the rutile phase predominates. For treatment times of 4 hours at all temperatures, the rutile structure was present. With treatment times of less than 4 hours, anatase was present. In addition, results showed that this simple, low cost technique can be an alternative method for depositions of TiO2 films, with the advantage of high levels of control over porosity, thickness and phase composition (anatase and rutile).