Resumo em Inglês:

In this research, the effect of stand-off distance on the interfacial mechanical and metallurgical properties of explosively bonded 321 austenitic stainless steel to 1230 aluminum alloy tubes was investigated. Interfacial microstructure was evaluated by optical microscopy and scanning electron microscope. Also, Microhardness tests were also carried out. The results show that with increasing of stand-off distance from 1 mm to 2.5 mm, thickness of intermetallic compounds at the interface increased from 3.5 µm to 102.3 µm, and also shape of interface was transited from smooth to wavy. The microhardness of the sample with 1 mam stand-off distance was 650 HV that increased to 927 HV in the sample with 2.5 mm stand-off distance which is related to intermetallic amount. The proportional amount of strength were 103.2 MPa and 214.5 MPa in the above samples respectively.

Resumo em Inglês:

The microstructure of the root pass in a superduplex stainless steel multipass welding was investigated.Results showed that the welding metal has an austenite matrix with particles of sigma phase formed in the ferrite/austenite interface and intragranularly.Eventhough the filler metal is intended to keep the phase balance after welding,the welding metal presented a considerable decrease in the ferrite content and a high proportion of sigma phase. Despite the exposition to thermal cycles on every pass, the heat affected zone presented a microstructure consisting of ferrite and austenite with a small proportion of sigma phase.Therefore,the thermal cycles of every welding pass allowed the decomposition of ferrite into austenite and sigma phase in points close to the heat source, changing the final microstructure.

Resumo em Inglês:

In this work, it was prepared hybrid membranes of polyamide6 (PA6) with montmorillonite (MMT) and porogenic agent (CaCl2). The hybrid membranes with CaCl2 were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), porosimetry by mercury intrusion (PMI), flux measurements and rejection. By means of X-ray diffraction, it was revealed that the hybrid membranes with CaCl2 have an exfoliated and/or partially exfoliated structure. For FTIR and DSC of hybrid membranes with CaCl2, it was found that the spectra and the crystalline melting temperature remained virtually unchanged compared to PA6 membrane. From the SEM images, it was observed that the addition of the MMT and the CaCl2 in the membrane of PA6 caused an increase in the amount of pores the surface and cross section of these membranes. By PMI, it was observed that the presence of MMT and CaCl2 in the membrane caused an increase in the average diameters of pores. The water-oil separation tests, indicated a significant reduction of oil in the permeate, allowing treatment of wastewater contaminated with oil.

Resumo em Inglês:

Biodegradable compounds of poly(ε-caprolactone) (PCL)/ cotton linter were melting mixed with filling content ranging from 1% to 5% w/w. Cotton linter is an important byproduct of textile industry; in this work it was used in raw state and after acid hydrolysis. According to the results of torque rheometry no decaying of viscosity took place during compounding, evidencing absence of breaking down in molecular weight. The thermal stability increased by 20% as observed in HDT for PCL/cotton nanolinter compounds. Adding cotton linter to PCL didn't change its crystalline character as showed by XRD; however an increase in degree of crystallinity was observed by means of DSC. From mechanical tests in tension was observed an increase in ductility of PCL, and from mechanical tests in flexion an increase in elastic modulus upon addition of cotton linter, whereas impact strength presented lower values for PCL/cotton linter and PCL/cotton nanolinter compounds. SEM images showed that PCL presents plastic fracture and cotton linter has an interlacing fibril structure with high L/D ratio, which are in agreement with matrix/fibril morphology observed for PCL/cotton linter compounds. PCL/cotton linter compounds made in this work cost less than neat PCL matrix and presented improved properties making feasible its commercial use.

Resumo em Inglês:

Metallic glasses (amorphous alloys) have grown from a singular observation to an expansive class of alloys with a broad range of scientific interests. Their unique properties require a robust understanding on the structures at the atomic level while alloys in this class have a similar outlook on the microstructure. In this review, we went through the history of the majority studies on the structure models of metallic glasses, and summarized their historical contributions to the understanding of the structure metallic glasses and the relationship between their structures and properties.

Resumo em Inglês:

Polymer solutions of polysulfone (PSf) and methylcellulose (MC) in 1-methyl-2-pyrrolidone (NMP) were used to prepare ultrafiltration membranes by the phase inversion technique via immersion precipitation. The effect of MC additive on the structure and performances of the membranes was studied. The obtained membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), infrared spectroscopy (FTIR-ATR), equilibrium water content (EWC), water contact angle, porosity and ultrafiltration experiments of polyethylene glycol solutions. It was found that all the PSf/MC membranes had higher porosity, more hydrophilic surface and more vertically finger like pores than PSf membrane. With an increase in MC content in the casting solution from 0.5% to 1.5%, the hydraulic permeability increases from 17.17 to 118.46 L.m-2.h-1.bar-1, while the rejection decreases from 91.82% to 64.45% with PEG 35000. DSC scan and FTIR analysis confirmed that methylcellulose was trapped in the membranes matrix.

Resumo em Inglês:

A multi-layer scaffold that incorporates bioglass, phosphatidylserine and steroidal saponins loaded collagen microparticles was prepared in this study. Combinatorial processing techniques involving porogen leaching protocol and freeze-drying were used. Drug distribution and microstructure could be controlled mainly by the concentrations of drug-loaded collagen microparticles and porogen as well as freezing temperature for different layers of the scaffolds. Morphological observation, measurement of swelling properties, examination of drug release kinetics, and analysis of cell bioactivity showed that the resultant scaffolds had highly interconnected pores, gradient drug distribution and graded porous micro-architecture, similar swelling ratio for different layers, better drug release kinetics in view of lower initial release and slower average release rate compared to the scaffolds with homogeneous structure, as well as approving support of cell ingrowth. This study suggests that the optimized scaffolds have promising potential for applications in bone tissue engineering.

Resumo em Inglês:

Ultra high molecular weight polyethylene (UHMWPE) is one of the most important engineering materials owing to outstanding properties like impact strength and abrasion resistance. However, the relatively low Young´s modulus restricts some application and the use of fillers may be a suitable way to overcome this. The fillers can influence the photo stabilization of the compound, as it occurs to other polymers. Neat UHMWPE and its composites with 1 and 10% of iron ore fine were exposed to ultraviolet radiation for up to 33 days and then tested for mechanical properties. The stress-strain behaviour changed with degradation, with an evident necking and strain hardening region that was not observed before exposure, due to a reduction in entanglements density. From the tensile results, the filler may have a protection action against UV, particularly when a loading of 10% was present. Complementary analyses were performed, including X-ray diffraction, DSC and SEM.

Resumo em Inglês:

The concern for the environmental pollution and the prevention of resources has attracted researchers to develop new eco-friendly green materials based on sustainability principles. In this experimental study, there are six different composite samples were fabricated by using banana and carbon fibers with epoxy resin matrix. The mechanical properties such as tensile strength, flexural strength, impact strength, and water uptake properties of these composites have been evaluated. The composites reinforced with pure carbon fibers can hold the maximum tensile strength of 288.03 MPa, flexural strength of 3.12 kN, impact strength of 4.58 J and water intake percentage of 62.3%. Whereas the composites reinforced with carbon and banana fibers can withstand the maximum tensile strength of 277.06 MPa, flexural strength of 3.07 kN, impact strength of 4.36 J and water intake percentage of 70%. The finite element analysis has been carried out to predict the mechanical properties of the composites by using ANSYS 15.0. The experimental results are compared with the predicted values and have found that, there is a high correlation occurs between the results. Scanning electron microscopy (SEM) analysis is carried out to study the fiber matrix interfaces and analyse the structure of the fractured and water absorbed surfaces.

Resumo em Inglês:

The main aim of this study was to develop scaffolds based on alginate, chitosan and hybrid fibers with and without glycerol. The scaffolds developed underwent assessments for tensile property, swelling ratio and weight loss, cellular viability, degradation and biomineralization, as well as DSC/TGA thermal analysis. Tenacity values showed that use of glycerol and the interaction between alginate and chitosan as a hybrid fiber were associated with increasing tenacity values. In the swelling and weight loss study, the scaffolds containing glycerol presented lower weight loss and higher water absorption values in all scaffolds, compared to scaffolds without glycerol, indicating that glycerol acted as a stabilizer. None of the alginate, chitosan and hybrid scaffolds, with or without glycerol, decreased cell viability. On the third day of the biomineralization assay, chitosan without glycerol indicated the presence of apatite crystals. The degradation study showed that glycerol may have acted as a stabilizer.

Resumo em Inglês:

This study aimed to analyze the residual stresses and roughness in finishing milling of AISI 4140 steel, quenched and tempered up to hardness of 58 HRC. Machining operations were performed with the use of CBN inserts and by varying three basic cutting parameters (cutting speed, feed per tooth and cutting depth). Hardened materials are typically machined by abrasive processes, which in turn are more expensive and complex to be studied due to the undefined cutting geometry of the grinding wheel. A series of machining tests with milling process and CBN tools was implemented in order to study the resultant condition of the specimen´s surface. An experimental design was used and the results were statistically treated, enabling the generation of a model that aims to obtain roughness values due to the optimization of three adopted cutting parameters. The roughness values found in the range of Ra 0,16 to 0,4 µm indicate that it is possible to use the milling process with CBN tools for finishing, reducing machining time and the cost of the machined part. The generated residual stresses were compressive and the feed per tooth parameter showed greater influence in this result. The research was limited to test only one type of CBN insert, which was constantly replaced, preventing the influence of tool wear on responses. The geometry of the tool as well as the use of cutting fluid were not considered. Milling process with CBN inserts is confirmed as a possibility for replacing grinding process for finishing machining leading to significant gains in machining time. An optimized model was derived to predict the value of the roughness and three optimizations were made to specify the best cutting parameters to desirable answers such as better roughness, higher compressive residual stresses and low cutting forces, for example.

Resumo em Inglês:

This study investigated the softening mechanisms of the AISI 410 martensitic stainless steel during torsion simulation under isothermal continuous in the temperature range of 900 to 1150 °C and strain rates of 0.1 to 5.0s-1. In the first part of the curves, before the peak, the results show that the critical (εc) and peak (εp) strains are elevated for higher strain rate and lower temperatures contributing for higher strain hardening rate (h). Moreover, this indicated that dynamic recrystallization (DRX) and dynamic recovery (DRV) are not effective in this region. After the peak, the reductions in stresses are associated to the different DRX/DRV competitions. For lower temperatures and higher strain rates there is a delay in the DRX while the DRV is acting predominantly (with low Avrami exponent (n) and high t0.5). The steady state was reached after large strains showing DRX grains, formation of retained austenite and the presence of chromium carbide (Cr23C6) and ferrite δ at the martensitic grain boundaries. These contribute for impairing the toughness and ductility on the material. The constitutive equations at the peak strain indicated changes in the deformation mechanism, with variable strain rate sensitivity (m), which affected the final microstructure.

Resumo em Inglês:

Cu2(OH)PO4 microstructures were synthesized by the hydrothermal method using three different types cupric salts (Cu (NO3)2, CuSO4, Cu(CH3COO)2) as raw materials. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-visible-NIR absorption spectra were used to characterize the as-obtained products. The different anions (SO42-, CH3COO-, NO3-) have different shapes and polarities, which can generate different interactions in reaction bath, induced the difference of structure and morphology of the prepared Cu2(OH)PO4. The Cu2(OH)PO4 microstructures prepared form Cu(NO3)2•3H2O showed the best photocatalytic activity induced by near-infrared light to degrade 2,4-dichlorophenol (2,4-DCP) solution. Our work suggests that the active morphological surfaces as well as different coordination environments for the metal ions has an important influence on the photocatalytic performance of Cu2(OH)PO4 microstructure.

Resumo em Inglês:

Ostrich eggshells are a potentially abundant and a high purity and low cost source of calcium to produce β-Tricalcium Phosphate (β-TCP) and Hydroxyapatite (HA), important calcium phosphates used as biomaterials. Here, we use a wet precipitation procedure to synthesize these phosphates using ostrich eggshells as a source of calcium ions. The biphasic precipitated powder, calcined at 800ºC, is a mixture of both Hydroxyapatite and β-Tricalcium Phosphate, also known as the biomaterial Biphasic Calcium Phosphate (BCP). Physico-chemical properties of the final powder product show water and CO32- groups absorbed in the particles surface, 0.1 to 100 µm particles size distribution and 11.70 m2/g of specific surface area.

Resumo em Inglês:

2.25Cr-1Mo steels are widely used in thermoelectric power plants. Under operational temperatures, their properties degrade due to microstructural changes related to carbide coalescence and stoichiometric transformations. The extent of such microstructural changes is controlled by stress, temperature and time. Therefore, these factors can be used to evaluate damage and as life assessment tools for the individual component. In the past, ferrite-pearlite was the predominate microstructure in commercial Cr-Mo steel products, owing to the well-known methodologies for remaining life assessment based degradation. Currently, the ferrite-bainite microstructure obtained through a more economical route is most commonly used for this steel grade. However, there is no consensus in the literature about microstructural changes that can be used as a degradation pattern for ferrite-bainite steels. This paper compares the aged microstructures and creep properties of ferrite-pearlite and ferrite-bainite 2.25Cr-1Mo steels. Aging was conducted at 500, 575 and 600ºC until 2,000 h, and creep tests were performed at 575ºC under a stress of 100 MPa. Microstructural changes were characterized by optical microscopy scanning electron microscopy. Metallographic observations of the ferrite-bainite steel show a more stable behavior at the ageing temperatures and time considered. However, creep tests revealed that the ferrite-pearlite microstructure possesses a better rupture time performance. Carbide size distribution and stoichiometric evolution of the carbides provided by transmission electron microscopy support the creep behavior. These results show that the current techniques for evaluating microstructural degradation of 2.25Cr-1Mo steels must be reconsidered.

Resumo em Inglês:

Prediction of microstructure evolution and microsegregation is one of the most important problems in materials science. The dendritic growth and microsegregation provide a challenging simulation goal for computational models of solidification, in addition to being an important technological feature of many casting processes. The phase-field model offers the prospect of being able to perform realistic simulation experiments on dendrite growth in metallic systems. In this paper, the microsegregation and dendritic growth of hypoeutectic Al-Cu alloys under constant cooling rate was simulated using a phase-field model. The main new feature of the present model is based on the fact that the effect of the growth rate is incorporated via an effective partition coefficient that has been experimentally determined for a range of growth rates. It is shown that both models (Phase-field model and Scheil) have significant deviations from the experimental data when the equilibrium partition coefficient is considered in the calculations. Since the predicted results using the models yielded discrepancies from the experimental data, an experimental equation is adopted for calculating the effective partition coefficient from experimental data. The experimental equation is then adopted in the calculations of phase-field model and Scheil's equation, showing a good agreement with the experimental data.

Resumo em Inglês:

Zinc sulphide (ZnS) thin film were prepared using chemical bath deposition (CBD) process and tin (Sn) doping was successfully carried out in ZnS. Structural, morphological and microstructural characterization was carried out using XRD, TEM, FESEM and EDX. XRD and SAED pattern confirms presence of hexagonal phase. Reitveld analysis using MAUD software was used for particle size estimation. A constantly decreasing trend in particle size was observed with increasing tin incorporation in ZnS film which was due to enhanced microstrain resulting for tin incorporation. The particle size of prepared hexagonal wurtzite ZnS was around 14-18 nm with average size of ~16.5 nm. The bandgap of the film increases from ~ 3.69 eV for ZnS to ~ 3.90 eV for 5% Sn doped ZnS film which might be due to more ordered hexagonal structure as a result of tin incorporation. Band gap tenability property makes Sn doped ZnS suitable for application in different optoelectronics devices. PL study shows variation of intensity with excitation wavelength and a red shift is noticed for increasing excitation wavelength.

Resumo em Inglês:

The work aims the study of the corrosion behavior of nitride plasma-assisted PVD coated Ti-6Al-4V alloy in 2 M NaOH at 25 and 60°C, using open-circuit potential (OCP) versus time measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The uncoated Ti-6Al-4V alloy showed a passive behavior. The TiN and TiAlN/TiAlCrN coated Ti-6Al-4V alloy also presented a passive behavior and the corrosion potential remained at the same range when compared with the potential of the uncoated alloy. The TiN hard coating showed a superior corrosion resistance, which was evidenced by lower corrosion current densities and higher impedance values. The increase in temperature decreased the corrosion resistance of both uncoated and coated alloy in NaOH.

Resumo em Inglês:

In this study, cerium-based conversion coating was deposited on steel X52 by dip immersion method. Cerium oxide/hydroxide is an environmentally friendly conversion coating. The effects of immersion times and immersion temperatures on corrosion properties of cerium conversion coating on steel X52 were studied. Its corrosion resistance in 3.5 wt.% NaCl solution was investigated by means of electrochemical impedance spectroscopy, potentiodynamic polarization, and surface techniques. The coated samples showed a significant decrease in corrosion rate and corrosion current decreased with increasing immersion time up to 60 s. In addition, electrochemical impedance data showed that in the presence of cerium oxide conversion coatings, the charge transfer resistance of aluminum increased. The experimental results indicated that the corrosion resistance decreased with increasing the operating temperature. Surface morphology and its chemical composition were analyzed by means of scanning electron microscopy and energy dispersive spectroscopy.

Resumo em Inglês:

UV curing is simple, fast and effective procedure for enzyme immobilization with minimized enzymatic activity. UV-curable methacrylated chitosan is here proposed as a support material for immobilization of lipase. The morphology of the polymeric support was characterized by scanning electron microscopy (SEM). Both covalently (CIL) and physically (PIL) immobilized enzyme is analyzed in terms of enzymatic activity as a function of reusability, pH, storage, as well as stability under various experimental conditions. The recovery of activity of lipases immobilized onto a photo-crosslinked polymer network was 82.0% and 70.0% for CIL and PIL, respectively. The optimum pH value for the free lipase was at pH 6.0. The optimum pH of the both CIL and PIL was shifted to pH 7.0. Immobilization increased the thermostability of the lipase from 50 ºC to 62 ºC. The free enzyme lost all its activity within 15 days. Repeated batch experiments show that about 61% of the enzyme activity of CIL and 41% of PIL was retained after 8 cycles.

Resumo em Inglês:

DIN 1.4110 martensitic stainless steel is largely used in the cutlery industry due to its high corrosion resistance associated with high mechanical resistance. However, when this material works under corrosion and wear conditions at the same time, their synergistic effect can accelerate the degradation process of the alloy. Cryogenic heat treatments have been proposed to improve the dimensional stability and mechanical properties, since they minimize the amount of retained austenite. The aim of this work is to study the effect of deep cryogenic heat treatment at -80 ºC and at -196 ºC on the corrosion resistance and tribocorrosion behavior of DIN 1.4110 martensitic stainless steel. The microstructure, hardness, corrosion resistance and tribocorrosion behavior were evaluated. Although the heat-treated samples presented higher hardness and lower corrosion current density (icorr) compared to samples in spheroidized condition, their material removal under tribocorrosion conditions increased, which demonstrated the synergy between corrosion and wear.

Resumo em Inglês:

The supermartensitic stainless steels (SMSS) are a relatively new class of corrosion resistant alloys developed to obtain a better combination of weldability, strength, toughness and corrosion resistance than conventional martensitic stainless steels. The final properties of SMSS are strongly influenced by quenching and tempering heat treatments. In this work, different routes of heat treatments were tested in a Ti-stabilized 12%Cr supermartensitic stainless steel with the objective to improve mechanical properties, specially the low temperature (-46ºC) toughness. Double and triple quenching were tested and compared to single quenching heat treatments. Two tempering temperatures (500ºC and 650ºC) were tested. The results obtained with instrumented Charpy impact tests showed that a triple quenching treatment was able to increase the density of fine TiC particles and improve the mechanical properties of specimens heat treated by quenching and tempering at 650ºC.

Resumo em Inglês:

Slag foaming is part of steelmaking process and could bring several benefits: it helps to save energy, improves productivity, enhances the refractory service life, decreases noise pollution and protects the bath from nitrogen incorporation. Unfortunately, slag foaming is a highly dynamic process that is difficult to control. There are factors that limit the quality of the foam generated on the slag, such as: basicity, FeO content, surface tension, viscosity, carbon and oxygen injection. This paper aims to discuss the main factor that induces foaming, mathematical models proposed by different authors and the use of isothermal solubility diagram (ISD) to predict the foam quality.

Resumo em Inglês:

Al films and TiO2 films were separately coated on AZ31 magnesium alloy substrates by means of magnetron sputtering method. The surface properties of the samples were explored and compared. Scanning electron microscope (SEM) observed the compact structure characteristics of as-deposited Al films and TiO2 films. After heat treatment under 200ºC for half an hour the films kept the compact structure characteristics and there didn’t exist structural defects on the surface of the films. Nano-indentation measurement results display that the micro-hardness of as-deposited Al film and TiO2 film reaches about 1.90 Gpa and 1.51 Gpa, separately. Al film is a bit harder than TiO2 film. Finally, the corrosion experiments in simulated body fluid initially indicate the different corrosion properties for Al film and TiO2 film. Al film presents more effective anti-corrosion properties than TiO2 film.

Resumo em Inglês:

N-F codoped TiO2 films were immobilized on stainless steel sheets through a combined approach involving a dip-coating technique and a hydrothermal treatment, followed by calcination at 400°C in the presence of air. Photocatalyst characterization was conducted using XRD, Raman and UV-VIS spectroscopy as well as SEM. The films were tested in a three-electrode cell for the photoelectrocatalytic degradation of CN-containing compounds. The results showed that the increase in the degradation rate of CN-containing compounds is both influenced by a synergistic effect of the doping agents and strongly dependent on the concentration of CN-containing compounds in the solution. Nitrogen contributed to the enhanced photoactivity under visible light due to the generation of localized states within the band gap of TiO2, whereas the presence of fluoride improved the superficial properties of the film, which resulted in higher amounts of CN-containing compounds that were degraded by direct charge transfer through the photogenerated holes.

Resumo em Inglês:

Surface integrity has significant effect on service performance of a component. The surface integrity of workpieces submitted to grinding process depends on the conditions of cooling produced by cutting fluids, which are used to avoid microstructural damage in the process. However, cutting fluids are harmful to the environment and human health, and appear as a crucial element to the optimization of the manufacturing process. In this scenario, biodegradable cutting fluids, such as formulations based on vegetable oils, appear as promising possibility to a cleaner production in grinding process. This study analyzed the surface integrity of AISI 4340 steel, quenched and tempered, in the external cylindrical plunge grinding process with the use of six different formulations of biodegradable cutting fluids (with oils of soybeans, corn, and mineral oil, pure and with additives). The performance of the application of cutting fluids was evaluated by characterizing the microstructure by Scanning Electron Microscopy - SEM and microhardness and roughness measurements. The results showed that the surface integrity of the components was not significantly damaged, which proves the efficiency of biodegradable cutting fluids and feasibility of its use in grinding process.

Resumo em Inglês:

In this work, the glass forming ability was studied in potassium phosphate glasses with increasing amounts of TiO2 in order to obtain a glass-ceramic with photocatalytic properties. The first studied series has been the binary system (100-x) KPO3-xTiO2. Homogeneous and transparent glasses could be obtained with x varying from 10 to 30 mole%. Since the photocatalytic anatase phase could not be precipitated in this system, the ternary system KPO3-TiO2-Nb2O5 was investigated in order to incorporate higher TiO2 contents without spontaneous crystallization under cooling. Thermal properties of all glass samples were investigated by DSC and allowed identifying an increase of glass transition temperatures with increasing TiO2. For all compositions, exothermic events related with crystallization were also observed and suitable heat-treatments resulted in specific crystalline phases identified by X-ray diffraction. Selective precipitation of the anatase titanium oxide was successfully obtained from the glass compostion 35KPO3-25Nb2O5-40TiO2 (KN25T40) after heat treatment at 720°C for 2 h, suggesting the possibility of obtaining a glass-ceramic for photocatalytic applications. Structural investigations by Raman were also performed on glasses and glass-ceramics and allowed to point out the glass intermediary behavior of TiO2 in the phosphate vitreous network where TiO4 and TiO6 octahedra are inserted inside the phosphate network with TiO6 clusters identified at higher TiO2 contents. Raman analysis also identified anatase TiO2 in the KN25T40 glass-ceramic.

Resumo em Inglês:

A mathematical model has been developed to simulate the nitriding process of plain carbon steel, considering the simultaneous diffusion of nitrogen in different iron-nitrogen (Fe-N) phases and the precipitation dynamics of γ' and ε iron-nitride. The model can predict the distribution of nitrogen concentration, volume fraction of Fe-N phases and hardness. Furthermore, a finite element method (FEM) post-process technology is presented to avoid the limit of FEM mesh improvement and time-saving. The uniform-sum-division algorithm is adopted as local refinement algorithm (LRA) of meshes. The modified inverse distance weighting (IDW) method is used to interpolate the FEM simulated results. Then, the nitriding model and post-process technology are incorporated within the framework of the developed FEM code COSMAP (COmputer Simulation of MAnufacturing Process) based on metallo-thermo-mechanical theory. In order to validate the nitriding model and FEM post-process technology, the nitriding process of S30C steel is modeled by COSMAP software. The simulated distributions of nitrogen content and hardness are consistent with the measured ones. In addition, the simulated results at different mesh size are compared for two-dimensional model. It is indicated that the interpolated results agree well with the simulated results of fine mesh model and the experimental ones.

Resumo em Inglês:

This research presents the influence of manufacturing processes and heat treatments on the resulting microstructures and mechanical properties of an API 5L PSL2 seamless steel pipe. Three different conditions are considered - as rolled, normalized and quenched and tempered - to obtain the grades X42R, X42N and X70Q, respectively. Scanning electron microscopy techniques was used to characterize the resultant microstructures. Tensile, hardness, impact, fracture toughness (J integral) and fatigue crack growth tests (da/dN x ΔK) were used to study the materials mechanical behavior. The results show the possibility of achieving API grades for a seamless pipeline steel, through suitable heat treatments. The microstructural modifications and mechanical properties changes observed showed a remarkable structure-properties relationship of the steel, and attempt to a proper selection as required by the structural design. The quenching and tempering process increased tensile mechanical properties and fracture toughness, but combined to a significant decrease in fatigue crack growth resistance.

Resumo em Inglês:

The Linearized Augmented Plane Wave method, as implemented in the Wien2k computational code, was used to investigate the effects of the 3d transition metals (TM) Sc, Ti, and V impurities on the hyperfine interaction of iron atoms in α-Fe. The calculation results of this study suggest that the introduction of a TM (TM = Sc, Ti, and V) impurity into α-Fe increases the size of the lattice as well as alters the electronic charge distribution between the atoms in the lattice and at the atomic sphere of the host Fe atoms. The increase of the lattice disturbs the position of the iron atoms and the change on the electronic distribution disturbs the hyperfine interactions at all iron nuclei. The disturbances on the hyperfine magnetic field, isomer shift and electric field gradient at the iron nuclei depend on its relative location to the impurity atom.

Resumo em Inglês:

Impedance Spectroscopy was performed to examine the electrical conductivity on KH2PO4 KDP, (NH4)H2PO4 ADP and K1-x(NH4)xH2PO4 (x = 0.076, 0.118, 0.357, 0.857, 0.942) crystals with increasing temperature. They were grown by solvent evaporation method. Zview simulation software was used to theoretically fit electrical conductivity results as a function of frequency (1-106 Hz) and temperature (20-160 ºC) with equivalent circuits. These dielectric-type materials become ionic conductors upon heating. Proton jumps in hydrogen bonds, heavier ions migration (K+ and NH4+), and rotation and reorientation of ammonium groups contributed to electrical conduction. This conduction behavior follows the Arrhenius equation with which the activation energies were determined at different temperature ranges. For ADP-rich (x > 0.8) and pure ADP crystals the conductivities are higher than those for KDP-rich (x < 0.2) and pure KDP. Lattice defects may reduce electrical conductivities in the crystals with intermediate x composition. Complex permittivity ac and complex conductivity ac were also obtained for these crystals.

Resumo em Inglês:

BaTiO3 doped with Gd3+ (Ba1-xGdxTi1-x/4O3) was synthesized using the solid-state reaction method with x = 0.001, 0.003, 0.005, 0.01, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, and 0.35 Gd3+ (wt. %). The powders were decarbonated at 900 ºC and sintered at 1400 ºC for 8 hours. The tetragonality of the synthesized Gd3+-doped BaTiO3 particles was analyzed. XRD patterns and Raman spectra revealed that the crystal phase of the obtained particles was predominately tetragonal BaTiO3; the intensity of the Raman bands at 205 cm−1, 265 cm−1, and 304 cm−1 decreased when Gd3+ was increased. A secondary phase (Gd2Ti2O7) was found when the Gd3+ content was higher than 0.15 wt. %. The capacitance of the sintering pellets was measured at 1 kHz; these values were used to calculate the relative permittivity, the maximum permittivity values were recorded for the samples with x = 0.001, 0.005, and 0.1.

Resumo em Inglês:

The objective of this work is the Hot Filament Chemical Vapor Deposition (HFCVD) of diamond films on stainless steel substrates using a new technique for intermediate barrier forming, made by laser cladding process. In this technique, a powder layer is irradiated by a laser beam to melt the powder layer and the substrate surface layer to create the interlayer. The control of the laser beam parameters allows creating homogeneous coating layers, in rather large area in few seconds. In this work, the silicon carbide powder (SiC) was used to create an intermediate layer. Before the diamond growth, the samples were subjected to the seeding process with diamond powder. The diamond deposition was performed using Hot-Filament CVD reactor and the characterizations were Scanning Electron Microscopy, X-ray diffraction, Raman Scattering Spectroscopy and Scratch Test.

Resumo em Inglês:

N-doped TiO2 can be deposited by reactive magnetron sputtering by two methods: incorporation of nitrogen particles in the TiO2 lattice or incorporation of oxygen particles in the TiN lattice (oxidation). This paper investigates both procedures by experimental and numerical methods in order to establish the best way for incorporation of substitutional nitrogen in the TiO2 lattice. Films were deposited with different oxygen and nitrogen flow rates for fixed values of argon flow rate, working pressure, DC power, film thickness and target-to-substrate distance. After deposition, samples were characterized by optical spectrophotometry to calculate the energy gaps. The mechanism for incorporation of substitutional nitrogen was investigated by a numerical model based on Berg model, where data were faced to experimental data in order to validate the growing mechanism. Results indicate that the deposition with oxygen flow rates lower than that set for nitrogen decreases the energy gap due to the incorporation of substitutional nitrogen in the film lattice and depositions with high oxygen flow rates decrease the amount of nitrogen in the film lattice due to the fast oxidation of the nitride layers caused by the high sticking coefficient of the oxygen particles.

Resumo em Inglês:

In an effort to show the influence of the hybridization method in hybrid fabric reinforced composites within the characteristic of the fracture and the mechanical properties, two laminate reinforced with bi-directional woven were developed, where one of them was reinforced with a hybrid strand (hybrid strand composite laminate) and the other with a different strands (hybrid fabric composite laminate). Both laminates used polyester resin, Kevlar-49 and glass-E fibers, had four layers and were prepared industrially by hand lay-up manufacturing. The percentages by weight of fiberglass and Kevlar in each type of woven are equal. The hybrid strand composite laminate showed a higher tensile strength, however the hybrid fabric composite laminate showed superior properties in three-point bending test, for example, 41.7 % superiority in flexural strength. The results showed that the hybridization method in hybrid reinforced composites influences the mechanical behavior of laminates and the formation and spread of damage.