Resumo em Inglês:

In this study, the numerical analysis of instrumented indentation testing was combined with the experimental procedure to evaluate the mechanical properties and thickness of a titanium nitride (TiN) film deposited on titanium substrate (Ti) by plasma processing. TiN film thickness is an important parameter for the surface treatment industry. In numerical analysis, the finite elements method (FEM) was applied using Marc™ commercial software. Initially, the mechanical properties of the film and substrate were determined using a numerical-experimental methodology, combining the results of indentation testing with a Berkovich indenter and the same numerical simulation for both the film and substrate. Next, the behavior of instrumented Vickers hardness as a function of maximum indenter penetration depth (hmax) was compared with the numerical results of this hardness as a function of the ratio between penetration depth and film thickness (hmax/t). Both curves were fitted using power law equations, which calculated film thickness applying a new convergence algorithm. Finally, it also was shown that the film thickness obtained agrees with the experimental range reported in the literature.

Resumo em Inglês:

Aluminum alloys of the 7xxx series (AA7075) are preferred in the aerospace and automotive industries due to their low densities, high strength, good corrosion resistance properties. Additionally, these alloys show the most effective aging properties among aluminum alloys. For this reason, it is very important to determine the most appropriate aging parameters for microstructural development. Literature review reveals that the effect of pre-strain on springback has not been studied yet. In this study, the effects of aging temperature, time, and pre-strain on mechanical properties are investigated for AA7075. Precipitates present in solid solutions of AA7075 and their effects are examined. Results reveal that MgZn2 precipitation is not observed at aging temperatures of 120 and 160 ºC. After the formation of MgZn2 precipitates, microstructure becomes softer when aging continues at a higher temperature or longer period of time. It is clearly seen that pre-strain causes Portevin-Le Chatelier (PLC) effect after aging at 120 and 160 ºC for aging times of 30 and 90 minutes.

Resumo em Inglês:

This study investigated a conversion coating based on hexafluorozirconic acid solution on cold-rolled (AISI 1006) steel sheets, in situ, at different pH values and immersion times. Electrochemical characterization was carried out by electrochemical impedance spectroscopy (EIS) with hexafluorozirconic acid bath as the electrolyte. Laser scanning confocal microscopy (LSCM) was used to evaluate the morphology of the coating in situ, i.e., during the coating formation. According to the results, the polarization resistance (Rp) of the conversion coating is affected by the immersion time and by the pH of the conversion bath. The electrochemical analyzes point out conversion baths at pH between 3.5 and 4.5 and immersion times from 600 to 900 s as optimal operating conditions, achieving an average polarization resistance of 713 ± 107 Ω cm2.

Resumo em Inglês:

In this work, the semiconductor of ZnO-CoFe2O4 composites were prepared by green synthesis approach using rambutan peel extract (Nephelium lappaceum L.) as a capping agent. X-ray diffraction patterns of composites showed the main peaks of ZnO at 2θ = 31.8°, 34.5°, and 36.2° corresponding to hexagonal wurtzite structure and weak peak at 2θ = 35.4° for cubic structure of CoFe2O4. The formation of rice-like and small granular morphology were confirmed by scanning electron microscope (SEM) and transmission electron microscope (TEM), whereas the superparamagnetic behavior of the samples were determined by vibrating sample magnetometer (VSM). The spectrum of Fourier transform infrared (FTIR) and x-ray photoelectron spectroscopy (XPS) showed absorption bands related to a number of interactions and binding energy in the samples respectively. The photocatalytic performance of composites under solar light was evaluated for the degradation of Direct Red 81 and the dye from washing water of batik garments. The composites showed good photocatalytic activity with the degradation percentage reaching 99.6% for Direct Red 81 dye after 2 hours.

Resumo em Inglês:

The synthesis of mesoporous materials in macroscopic scale, as for example, the monoliths, has been of great interest in view of the wide range of applications that this material holds. Thus, this work consists of the production of silica monoliths for the purpose of they being used in the carbon dioxide (CO2) adsorption process. The adsorbents were prepared in pure form and also with addition of heteroatoms: Al, Ti and Zr. The samples were then functionalized with pentaethylenehexamine (PEHA) by the wet impregnation method. The materials were characterized by the following techniques: X-ray diffraction (XRD), textural analysis, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and Thermogravimetry (TG/DTG). The analyses indicated that the materials synthesized with heteroatom incorporation presented a disordered pore structure and high surface area (1387 m2/g for sample Ti/M1). In addition, they showed a significant increase in adsorption of CO2 relative to their parent sample, a fact that is not much explored in the literature. The CO2 adsorption performance tests were carried out at 30 ºC and atmospheric pressure. All functionalized materials demonstrated improved CO2 adsorption capacity relative to their starting samples. Adsorption capacities up to 111.3 mg/g were found in this work, which makes the materials developed promising candidates for the capture of CO2.

Resumo em Inglês:

This paper proposes an alternative to the Avrami equation capable of describing whole transformation curves with significant fitting-correlations. The model bears physically meaningful parameters which permit considering the initial transformation kinetics independently from the subsequent microstructural evolution. Data of martensite, bainite, recrystallization, and pearlite transformations validate the model. Further to the expeditious description of transformation curves, the model guides the modeling of specific mechanisms.

Resumo em Inglês:

There is increasing interest in the ceramic industry in the development of pigments with intense tonalities that can be produced from low-cost alternative raw materials and also can fulfill technological and environmental requirements. This work reports on the preparation and characterization of CdS yellow ceramic pigment derived from Ni-Cd batteries through an acid leaching process. Cadmium was chemically extracted with HCl and tributylphosphate (TBP) and reacted with H2S to form CdS. The obtained yellow powder is composed of agglomerated particles with nanometer sizes and hexagonal and rod-shaped crystals. Rietveld refinement indicated that these particles consist of cubic and hexagonal CdS. CIELab colorimetric parameters revealed a bright yellow color (L*=77.8, a*=13.7 and b*=76.2), similar to that of commercial Cd Yellow pigment. The extraction of Cd from Ni-Cd batteries could be a low-cost and environmentally friendly solution for the production of CdS-based ceramic pigments.

Resumo em Inglês:

Mechanical alloying (MA) can be highlighted among the various methods and powder processing forms, which consists of producing homogeneous materials from elementary powders. This process is of paramount importance as it has the ability to reduce the particle size of the powders and can often promote bonding between elements which have low interaction and wettability. This method is usually used in the route of powder metallurgy, and generally improves the sinterability and mechanical properties of the materials. In this context, the objective of this work was to analyze the evolution of mixtures of Al2O3-5wt%-Ni and Al2O3-5wt%-Nb powders submitted to the mechanical alloying process in a planetary ball mill for up to 40h. The morphological evolution was observed through Scanning Electron Microscopy (Field Emission Gun, SEM-FEG), energy dispersive spectrometry (EDAX) phases and particle sizes by Particulometry. It was observed that a significant micro structural change occurred in both compositions, indicating the formation of composite powders. This behavior was more intensely observed with the increase in the grinding time, obtaining composite powders with a more homogeneous and uniform structure with the time of 40 hours of MA.

Resumo em Inglês:

Abstract: The influence of important factors related to fluid preparation on shear-thickening fluids (STF) is not well explored in literature. Thus, this paper aimed at analyzing the statistical significance of experimental conditions, such as fumed silica concentration (Cs), stirring time (tst), stirring speed (Sst) and sonication time (tso ), on the rheological behavior of fumed silica particles and PEG 400 dispersions. For that, a 2k factorial Experimental Design (DOE), with three center points, was accomplished. The investigated response variables were: maximum viscosity (ηm); critical shear rate (γ˙m) where the viscosity is maximum; and agglomerate size of particles during preparation (R). All factors were statistically significant for all three response variables. Higher viscosity values for shear rate range analyzed was obtained with longer tst, lower Sst and longer tso. An important contribution of this paper was to show discontinuous shear thickening (DST) for lower concentrations than previously found in literature only changing the preparation protocol.

Resumo em Inglês:

This work presents the characterization of austenite decomposition kinetics in two steels during continuous cooling considering non-deformed austenite grains. Two different chemical concepts of steels were evaluated: low carbon - high manganese and a relatively new concept based on low carbon - low manganese - high niobium contents. Dilatometric experiments, microstructural characterization procedures and microhardness tests were carried out. Experimental and calculated CCT diagrams were plotted and the adapted JMAK model was applied aiming to predict the austenite decomposition kinetics. The low carbon - high manganese steel was the most sensitive to the applied cooling rates and, due to that, presented the higher grain refinement and hardness increasing after continuous cooling. These results highlight that the Mn content decreasing may promote a potential loss of grain refinement in procedures of continuous cooling where the structure recrystallization does not occur, as in some welding procedures or conventional heat treatments applied in the seamed pipe manufacturing process.

Resumo em Inglês:

Bi2WO6 powders were synthesized by the molten salt method at 250-350 ºC using the mixture of Bi(NO3)3·5H2O and Na2WO4·2H2O as a precursor, and the mixture of LiNO3 and NaNO3 with a molar ratio of 27:33 as a molten salt, respectively. The effects of temperature and salt amount on the phase composition, morphology and photocatalytic activity under the visible light irradiation were investigated. The results revealed that pure phase Bi2WO6 powders could be synthesized at 350 ºC as the weight of molten salts were 2‒5 times as many as the precursor. Bi2WO6 powder synthesized with lower salt amount exhibited larger surface area, more abundant pores, narrower bandgap and lower PL intensity, all of which contributed a higher photocatalytic activity. The synthesized Bi2WO6 powder could degrade 0.01 mol/L Rhodamine-B solution by 97% after irradiation under visible light for 60 min. The obtained Bi2WO6 powder had a good photochemical stability and reusability, revealing potential application in environmental treatment.

Resumo em Inglês:

Influence of solid solution temperature on microstructures and corrosion properties of CoNiCrMo alloy were investigated by means of optical microscopy (OM), scanning electron microscope (SEM) and electronic differential system. The corrosion resistance of CoNiCrMo alloy in 0.9%NaCl aqueous solution was also investigated. The results indicated that with the increase of solution treatment temperature, the dendrites of CoNiCrMo alloy gradually disappeared. Thus, the corrosion resistance of the alloy decreased. When the solution temperature is 1200ºC, the dendrites almost disappeared and most carbide dissolved, and begins to spheroidization. The corrosion resistance of CoNiCrMo alloy treated at 1000ºC for 1h is the highest than the one at 1100 ºC and 1200ºC. Its self-corrosion potential is -424mV and self-corrosion current density is 1.02×10-8A/cm2.

Resumo em Inglês:

Waste printed circuit boards (WPCB) residues were mechanically processed to concentrate their metal content aiming to reduce costs of the subsequent recovery of copper, tin, and lead. A fully dry route was proposed to avoid the generation of liquid effluents that would require additional treatment. Firstly, 10.7% of the residue was segregated by magnetic separation; the remaining nonmagnetic fraction was comminuted and sieved. Ceramic and polymer materials (1/3 of the total weight) concentrated in the finer and the coarser size fractions, while metallic materials (2/3 of the total weight) concentrated in the intermediate size fraction (90.7, 94.5, and 95.6% of the total copper, tin, and lead contained in the milled WPCB, respectively). The fractions between 0.3-1.20 mm were submitted to gravity separation using a zig-zag air classifier; enrichment of copper (from 43±11% to 68±5%), tin (from 10±3% to 17±1%), and lead (from 4±1% to 6.4±0.5%) were obtained.

Resumo em Inglês:

In this work, scanning electrochemical microscopy (SECM) was employed to study the corrosion behavior of anodized AZ31B magnesium alloy exposed to simulated body fluid. SECM measurements were carried out in surface generation/tip collection mode. The hydrogen evolution flux caused during corrosion of the magnesium alloy was oxidized at the ultra-microelectrode (UME). Thus, this experimental procedure allowed evaluating the effect of the anodic protection in this alloy from the SECM analysis of Z- approximation curves, cyclic voltammograms and topographic maps. The results evidence differences in the local electrochemical response of magnesium alloy in the anodized and pristine conditions. The main sites of H2 evolution were verified in the magnesium alloy without anodizing at short exposure times.

Resumo em Inglês:

The SiO2-Al2O3-BaF2-TiO2-CaF2 transparent silicate glass-ceramics containing BaF2 nanocrystals were successfully prepared by heat treatment process through conventional melting method. Effects of heat treatment processes and Yb3+ concentration on the downconversion (DC) emission of the co-doped Er3+/Yb3+ transparent silicate glass-ceramics were investigated. With the increase of temperatures and times of heat treatment process, the DC emission intensity of the co-doped Er3+/Yb3+ glass-ceramics was significantly enhanced. At the same time, with the increase of Yb3+ concentration, the value of DC intensity of Er3+/Yb3+ co-doped bands centered at 849, 883 and 1533 nm is maximized when the concentration of Yb3+ reaches 2.5 mol.%. When the concentration exceed 2.5 mol. %, the DC emission intensity of Er3+/Yb3+ co-doped bands centered at 849, 883 and 1533 nm was decreased, owing to the self-quenching effect. It’s interesting that the DC emission intensity of Er3+/Yb3+ co-doped band centered at 978 nm didn’t quench when the Yb3+ concentration exceed 2.5 mol. %. At the same time, the DC mechanism and ET processes between Yb3+ and Er3+ ions were discussed.

Resumo em Inglês:

Thixoforming is the process of shaping near net shape metal components in a semisolid state. The process consists of preparing feedstock, reheating and shaping. Reheating the billet is the most critical step in thixoforming. Induction heating requires precise temperature control to obtain globular microstructure and prevent process defects, such as insufficient heating, overheating, and electromagnetic end effect and elephant foot phenomena. Moreover, inductive heating parameters are investigated to improve the quality of thixoforming. This study investigates applied coil current and optimal coil geometry and design (i.e. height, diameter and coil turn) in high-frequency induction heating numerically and experimentally. Simulation results combined with an approximation approach method are verified via a reheating experiment. The proposed method validated via an experiment can be a practical tool for predicting temperature distribution and reheating time required for thixoforming.

Resumo em Inglês:

In this work the influence of pre-treatment cleaning processes in the adhesion of TiN films deposited by the plasma based ion implantation and deposition (PBII&D) process over plasma nitrided AISI 316L stainless steel was investigated, varying the gas composition, the duration of the sputtering process and the temperature in the same deposition chamber. The TiN film morphology was scrutinized with scanning electron microscopy on the surface complemented with focus ion beam for the cross section. The film microstructure was characterized with X ray diffraction. The adhesion of the coatings was studied using the Scratch Test with constant load at different values and the Rockwell C indentation method as well. It was found that only with the sputtering carried out in a H2 - Ar gas mixing at 300 ºC temperature used as pre-treatment was successful to prepare the nitrided surface for the subsequent TiN deposition by the PBII&D process.

Resumo em Inglês:

Nanocrystalline bismuth telluride, Bi2Te3 has been synthesized by mechanical alloying (MA) the powder mixture composed of Bi and Te in the inert gas atmosphere within a short duration of 15 min. Microstructure characterization of the prepared powder has been investigated adopting the Rietveld’s method using X-Ray diffraction (XRD) data and analyzing high-resolution transmission electron microscopy (HRTEM) images. The XRD pattern of 15 min milled powder is composed of reflections of major Bi2Te3 phase with other two minor phases. Detailed structural information of these minor phases has been reported here which was not explored in any previous works. XRD analysis reveals that the stoichiometric Bi2Te3 phase has been formed after 1h of milling and there is no phase transition up to 10h of milling. HRTEM study also reveals the formation of single phase nanostructured Bi2Te3 phase. The DC (direct current) conductivities of 15min, 30min and 10h ball milled powders are measured within the temperature range of 359 to 633K. The electrical conductivity (σ) of Bi2Te3 indicates the semiconducting nature of the sample. There is no significant change of electrical conductivity of Bi2Te3 phase since its formation after 15min to 10h of milling, as there is no noticeable change in crystallite size.

Resumo em Inglês:

The aim of this study is to obtain and characterize surface layers on low carbon steel with the pack boron-nitro-carburizing process. Different mixtures of commercial powders (Turbonit® and Ekabor®) were used to investigate the case properties, microstructure and phases formation on AISI 1020 steel. A series of experiments were conducted in solid medium with powders blend, with weight proportions of 0/100;25/75;50/50;75/25;100/0 at temperatures of 1000 and 1100º C for 2 and 10 hours. Roughness measurement of all treated specimens was assessed to compare with pre-treatment condition. Hardness profile and comparative analysis of phase structure, morphology and composition was carried out to treatment conditions. Optical microscopy shows differences on layers surface, depth and microstructure case - diffusion zone. Results found indicated that for the same treatment time and temperature, hardness was changed, but the diffusion case depth was kept similar. DRX and XPS indicated the formation of boron nitride after certain treatments.

Resumo em Inglês:

Hot rolling experiments were designed to investigate the effect of rolling temperature and rolling deformation on microstructure, thickness and surface red scale of hot rolled mild steel oxide scale by spectrometer, SEM and pickling experiment. The research results show that in the same other experiment conditions, the greater the rolling deformation, the thinner the oxide scale extend; with the increase of rolling temperature, the plasticity of oxide scale is enhanced, the oxide scale can be compacted under a larger rolling reduction, which increase the adhesion of oxide scale to substrate and reduce the oxide scale falling off. The higher rolling temperature is, the greater the allowable critical deformation to inhibit red scale is, and the thicker tolerable thickness of the initial oxide scale is. In the process of hot strip rolling, improving rolling load distribution of the front frame and reducing the rolling deformation of the tail frame is helpful to control strip red scale and make oxide scale deform uniformly.

Resumo em Inglês:

The effect of the increase in crystalline defects in the structure generated by high-pressure torsion (HPT) on the corrosion behavior of metallic materials is not well understood. This report evaluates the influence of HPT on the corrosion behavior of a solution treated Al-3wt% Mg-0.2wt% Sc alloy in a 3.5 wt./v.% NaCl solution. The electrochemical behavior of the alloy was evaluated using cyclic polarization, electrochemical impedance spectroscopy (EIS), Mott Schottky, X-ray photoelectron spectroscopy, and chronoamperometry testing. The passive current density decreased after HPT processing, indicating a more protective oxide layer was formed on the surface of the HPT-processed alloy. Mott Schottky analysis confirmed the higher protection efficiency of the passive layer on the HPT-processed alloy. The film formed in the solution-treated alloy was a p-type and an n-type semiconductor while the alloy processed by HPT exhibited only an n-type semiconductor behavior. EIS showed that corrosion resistance in a saline medium increased with HPT processing.

Resumo em Inglês:

NbxAlyNz thin films were deposited by magnetron sputtering reactive technique with (y/x+y) ratio varying from 0 to 0.4, in order to maintain aluminum atoms inside NbN matrix in solid solution. GAXRD analyses revealed that the crystalline phase obtained for NbxAlyNz thin films was B1-NbN with a lattice constant shrinkage as Al concentration at these coatings was increased. Due to similarity in electro negativity values between Nb and Al, XPS analyses could not verify pronounced changes among as deposited NbxAlyNz coatings. The average hardness values evidenced that solid solution strengthening mechanism did not increase hardness significantly. The oxidation resistance increased with Al content and no oxide phases were registered by GAXRD analyses for coating with more aluminum added. However, SEM images revealed bubbles after oxidation at high temperatures for all samples.

Resumo em Inglês:

Antireflection coatings (ARC), not only reduce the reflection of the incident radiation but also protect the surface from environmental degradations. In present study, three- layer design was theoretically calculated and experimentally realized on the surface of lead chalcogenide, which had high refractive characteristics. First the theoretical designs of three- layers of different dielectric materials (i.e., ZnSe, SnO2, SiO and MgF2) were simulated using optical matrix approach. Subsequently, the developed designs were experimentally produced on lead sulfide thin films using thermal evaporation technique. The efficiency of the designs was evaluated for 1500-2400 nm spectral range and found that the design comprising ZnSe-SiO-MgF2 had 23% better performance than ZnSe-SnO2-MgF2, besides consistent coating adhesion and morphology. The difference between theoretical and experimental results was less than 10 and 16 % for ZnSe-SiO-MgF2 and ZnSe-SnO2-MgF2, respectively.

Resumo em Inglês:

In our research group, controlled release systems for the sulfentrazone herbicide has been accomplished by encapsulating this bioactive compound into calcium alginate (Ca-ALG) biodegradable polymer fashion and the release mechanisms were verified by using Korsmeyer-Peppas model (KP). However, the KP model does not allow to evaluate all the phenomena involved in the (Mt/M∞ versus t) curves. Thus, the aim of this work is the development of a new mathematical model to interpret the distinct regions of the controlled release assays of the Sulfentrazone herbicide encapsulated in Ca-ALG microparticles and that can be used for other systems with a similar release profile. The proposed model is based on the herbicide diffusion, dissolution and polymer surface erosion. The results show that the proposed model is closest to the experimental curve when compared to the KP. The new mathematical model allows not just to describe the behavior of the system in terms of Fick’s law, but to know what type of mechanism act in the herbicide release process.

Resumo em Inglês:

The effects of friction coefficient on formability behavior of advanced high-strength steel sheets have been examined in this study. For this purpose, forming analysis has been conducted by stretching the three different steel sheets such as DP600, DP800 and DP1000. Forming processes have been done by using punch that has different friction coefficients (0.05, 0.15, 0.3, 0.6 µ) in nakajima forming die. As a result of the analysis, it has been observed that thinning amount and forming force have increased by the increasing in the friction coefficient. When major and minor deformations on the sheet have been examined, it has been determined that the increasing friction coefficient makes plastic deformation amount increase.

Resumo em Inglês:

This work is a study of the microstructural properties of the polycrystalline ternary compounds AgIn5S8, AgIn5Se8, and AgIn5Te8 by X-ray diffraction technique (XRD). The full-width-half-maximum (FWHM) of the XRD profile is measured as function of the diffraction angle and used to estimate the microstructural parameters. In general, a microstructural characterization by XRD is principally performed by Strain/Size analysis based on the modified Scherrer formula, which in turn, allows for mean grain size and average microstrain to be computed. However, when applied to polycrystalline bulk semiconductors, the modified Scherrer formula gives grain sizes of the order of a few hundreds of nanometers, which is not usually observed in bulk materials. Instead, a new theoretical scheme with misfit dislocations and plastic deformations would be used to calculate the grain size into a bulk. Assuming that these dislocations are of elastic origin, we were able to calculate the misfit dislocations density as function of the elastic constants of the materials. With this, the modified Scherrer formula is corrected to explain the additional XRD line broadening. All microstructure parameters of our samples increase as the atomic radius of the VI-element increases, with elastic constants similar to related semiconducting compounds.

Resumo em Inglês:

The Carbon Fiber Reinforced Polymer (CFRP) laminate structural components used in the aerospace and military domains require high precision and strong stability. Usually the deformation of these structural components is difficult to be measured directly during operation, but the deformation of the CFRP laminate structure can be reconstructed with strain information. The CFRP laminate structure can be designed to adapt to the requirements of different applications through layering of variable thickness. In this paper, aiming at the discontinuous stiffness and strength of the variable laminations within the CFRP laminate structure, the BP neural network is proposed to be applied to the deformation reconstruction of CFRP laminates. With strain as input and deformation as output, based on a large amount of experimental data, the BP neural network model between strain and deformation is obtained through training. In this paper, CFRP test piecs with equal thickness and variable thickness were designed, and the corresponding strain-deformation reconstruction experimental system was constructed. The strain on the surface of CFRP test piece was measured by the fiber grating sensor, and the deformation of the test piece was measured by the laser displacement sensor. The comparative analysis between the predicted deflection obtained by neural network reconstruction and the actual measured deflection shows that BP neural network can reconstruct the structural deformation of CFRP laminates within certain error range.

Resumo em Inglês:

The scientific community has shown a growing interest in relating to the ferroelectric materials and it has made an effort to develop them. Among these several ferroelectric materials, we proposed to investigated Pb(ZrTi)O3 doped with distinct Er+3 concentrations. Our aim was to investigate how the erbium affects the PZT electrical properties. To determine the ideal sintering temperature of our ceramic samples, the dilatometry tests were performed. These results have showed that the erbium caused a change in sample densities (91.9% < ρ < 99.0%) as compared to undoped PZT sample. Furthermore, the X-ray diffraction results indicated that all samples are monophasic and peaks are indexed to tetragonal crystalline structure. According to these also results, there was an increment of the parameter a and a reduction of parameter c as compared to undoped PZT sample. On the other hand, the average grain size have decreased with the increment of erbium content. The electrical characterization of ours ceramics showed a peculiar ferrelectric-paraeletric phase transition around 390 ºC. Finally, the ferroelectric hysteresis measurements for doped samples in site A have revealed that remnant polarization and coercive field values depend on content. Whereas, doped samples in site B, the corresponding values are similar.

Resumo em Inglês:

In this work a re-investigation of the solubility limits of the (Nb), Nb3Al, Nb2Al and the Nb-rich side of the NbAl3 phases on the Nb-Al system is presented. Alloys in the binary fields ((Nb)+Nb3Al, Nb3Al+Nb2Al and Nb2Al+NbAl3) were arc-melted, and then equilibrated at 1000, 1200 and 1400 ºC. The phases were confirmed via X-ray powder diffractometry, and their compositions were determined via EPMA measurements. The results showed agreement with the literature concerning the solubility limits of (Nb), Nb3Al and NbAl3 phases, while important differences in the values were found for the Nb2Al phase. In addition, the lattice parameters of the Nb2Al phase were determined via Rietveld refinement. This new set of more accurate experimental information indicates that a thermodynamic reassessment is necessary to precisely describe this system.

Resumo em Inglês:

The SAXS and SANS techniques are widely applied to the structural characterization of materials at the nanometer scale. We here report quantitative analyses of the published literature related to these techniques and to relevant features of the International SAS Conferences. A total number of 42,048 articles related to SAXS and SANS were retrieved. The annual total number of published articles related to SAXS exhibits a fast and persistent growth from 1990 until 2018 while those referring to SANS remained essentially constant along the past two decades. Furthermore, the number of citations of articles published by authors from the USA and from some European countries (Germany, France, UK) are significantly higher than those published by authors from other countries. The persistent increase in the number of published articles related to SAXS around the world and particularly in Brazil is well correlated with the also increasing number of open synchrotron sources.

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Utilizing high chromium and nickel content in AISI 304 steel confers its good corrosion resistance. However, the high content of chromium and nickel increases the steel susceptibility to corrosion caused by the high concentration of chlorine. Consequently, the electrochemical and mechanical performance of the steel degrades. In this study, the effect of adding a layer containing a gelatin-dispersed mix of TiO2-ZrO2 nanoparticles on the corrosion rate and critical pitting potential of AISI 304 steel is studied. Two mix ratios of TiO2-ZrO2 nanoparticles to gelatin (0.5:0.5, 0.3:0.7) were used. Three different fractions of nanoparticles (1 wt. %, 2 wt. %, 3 wt. %) were used for each ratio. Potentiodynamic polarization examinations were used to measure the corrosion rate and the critical-pitting potential of the spin-coated AISI 304 steel in a simulated environment containing 3.5 wt. % NaCl. Scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) were used to study the morphology of the coated surfaces and the elemental composition of the nanocomposite coatings. The results show that the hybrid TiO2-ZrO2 nanoparticles coatings significantly improved the uniform and localized corrosion of the AISI 304 steel. Moreover, the results confirm the formation of homogeneous, stable, and crack-free coatings.

Resumo em Inglês:

Yield strength and toughness in steels are directly associated with hot forging processes, especially by controlling austenitic grain size and cooling conditions. The phenomenological JMAK model in macroscale has been applied in different material classes to predict grain size after hot forming. However, on an industrial application, there is still a lack of understanding concerning the synergic effects of strain rate and temperature on recrystallization. This preliminary study aimed at investigating the applicability of coupled semi-empirical JMAK and visco-elastoplastic models in numerical simulation to predict austenitic grain size (PAGS). Hot forging of cylindrical samples of a ferritic-perlitic DIN 20MnCr5 steel was performed followed by water quenching. The main influences, such as temperature, strain and strain rate fields following the recrystallization model were investigated using the subroutine of FORGE NxT 2.1 software. The results were evaluated by comparing experimentally measured and simulated PAGS at process end. The forging process generates different strain and strain rate fields in the workpiece, which in turn lead to a variation in the PAGS and recrystallization fractions. The simulation was able to detect the PAGS variation showing a good agreement between the experimental forging results and the applied model.

Resumo em Inglês:

The Norton-Bailey equation was used to simulate by finite elements the hardening and dynamic recovery of copper during the hot compression tests. The constants of Norton-Bailey equation were determined from the Voce-Kocks model. The simulation assumes a Mortar Contact with Coulomb friction and axial symmetry. Numerical results were compared with experiments. Six compression tests were carried out at 804 K, three with a strain rate of 0.1 s-1 and three with a strain rate of 1 s-1. The results show: The differences between the experiments and the simulations are less than 7.69% for strain rates of 0.1 s-1, and less than 0.67% for strain rates of 1 s-1. This shows that the simulation of hardening and dynamic recovery of hot copper is possible with the Norton-Bailey equation. Better numerical results were obtained when the behavior of copper is typical of hardening and dynamic recovery, and this happen for high values of strain rates.

Resumo em Inglês:

The microstructural evolution and phase transformation of a Ti-5Nb-5Al alloy during isothermal annealing treatment were studied in this paper. The microstructural evolution was analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) equipped with X-ray energy dispersive spectroscopy (EDS) and electron backscattering diffraction (EBSD). The first-principle calculation by density functional theory method was performed to analyze the effect of niobium diffusion on the α to β transformation. The results showed that the α phase initially grew by merging neighboring grains and then by boundary splitting with increasing the solution time below the β-transus temperature. However, the α phase disappeared absolutely above the β-transus temperature. According to the thermodynamic analysis by DFT calculations, the diffusion of niobium from β to α phase can promote the α to β transformation. After quenching in water, the acicular α’ phase precipitated from β matrix with an orientation relationship of {110}bcc||{0001}hcp and <111>bcc||<1120>hcp, and thus increased the hardness of the alloy.

Resumo em Inglês:

This paper reports on the effect of scanning speed on the laser deposited Cu on titanium alloy substrate. The experiments were conducted by varying the scanning speed from 0.3 m/min to 1.2 m/min while the laser power, the powder feed rate and the gas flow rate were kept constant. The laser deposited Cu were characterized through the evolving microstructure and surface roughness. Dendrites and acicular were much pronounced in the clad area; found to decrease as the scanning speed increases due to the laser interaction time and the cooling rate. These however, influenced the irregularities in the peaks and valleys of the surface texture. The arithmetic mean deviation, Ra were measured and abridged from 6.70 µm to 1.41 µm as the scanning speed was increased from samples DC1 to DC4. The motivation for this work is to improve the surface performance of Ti6Al4V alloy when exposed and attacked by marine microfouling organisms.

Resumo em Inglês:

Nickel ferrite (NiFe2O4) was synthesized by mixing stoichiometric amounts of α-Fe2O3 and NiO using mechanical milling and heat treatments at high temperatures. The physical characterization of the samples was carried out using X-ray diffraction, infrared and Raman spectroscopies, Mössbauer spectrometry, magnetization measurements, scanning electron microscopy and energy dispersive X-ray spectroscopy. We found that NiFe2O4 production increases from 81 to 100 wt. % with increasing temperature. Additionally, the lattice parameter and the saturation magnetization increase with increasing temperature. On the other hand, Mössbauer spectrometry showed that there is a decrease in the subspectral areas ratio for Fe3+ cations at tetrahedral (A) and octahedral [B] sites, AA/AB, with the increase of the temperature. In the SEM micrographs it was observed that the samples consisted of particles with irregular shapes and micrometric sizes. From IR spectra, the intensity of the 411 cm-1 band (vibrations at octahedral sites) increases relative to the intensity of the 599 cm-1 band (vibrations at tetrahedral sites) with increasing temperature. From the results obtained in the magnetization curves, it was possible to confirm the synthesis of NiFe2O4. As the heat treatment temperature increases, hysteresis loops with S-type geometric forms were obtained. All the results suggest that a defective spinel NiFe2O4 is formed at 1000 °C, and that as the temperature increases, the defects gradually disappear. Neither cation reordering phenomena nor possible evaporation of chemical elements were the dominant effects to account for the results. The results can be explained if it is assumed that [B]-sites cation vacancies are gradually filled with cations as the temperature of the heat treatment increases.

Resumo em Inglês:

The use of corrosion inhibitors is one of the most common methods to combat acid corrosion. The current studies aim to apply natural products as corrosion inhibitors, once the most used compounds are mostly toxic to the environment and to humans. The present paper purposes the application of an aqueous extract of agro-industrial waste (AEAW) to inhibit the corrosion of stainless steel AISI 304 in sulfuric acid. Gravimetric and electrochemical experiments were performed. The gravimetric experiments revealed that the extract acts as an inhibitor for stainless steel, showing inhibitory efficiency up to 81.6%. The electrochemical tests show that the AEAW makes the steel surface more noble. The extract acts by adsorption in the metallic surface, following a Temkin isotherm. The results indicate that the AEAW is a promising substitute of conventional organic compounds as a corrosion inhibitor to AISI 304 stainless steel in sulfuric acid.

Resumo em Inglês:

Friction Stir Welding (FSW) is an excellent alternative for joining dissimilar and similar materials in comparison to conventional welding processes. In this sense, this work aims at qualifying FSW to similar AA5083-O and AA5052-O aluminum alloys, with 6.35 mm thickness, in a CNC machining center. Therefore, four welding experiments were undertaken. At first, two types of plate surface finish were considered before joining. Afterward, two tool probe geometries, and changes in the base material position were evaluated. Hence, the welds were mainly analyzed by metallography, tensile testing, and bending tests. Results showed that the machining step to oxides removal and plates alignment is beneficial for the weld processing and the factor that has significant influence to achieve suitable joints is the tool probe geometry. Finally, by obtaining an average ultimate tensile strength (UTS) of around 191 MPa, enhanced microhardness, and bent angle of approximately 150°, the best joint was chosen.

Resumo em Inglês:

An approach following the null-matrix, Ti/Zr ratio of 2.08, for neutron diffraction was used to calculate the glass formation in Cu-Ti-(Hf,Zr) alloys. The Cu55Zr14.6Ti30.4, Cu61.48Hf18.52Zr6.48Ti13.52, Cu58.1Hf16.9Zr8.1Ti16.9 and Cu52.46Hf14.2Zr10.8Ti22.54 compositions (at. %), were calculated and prepared by argon arc melting. Copper die suction casting was employed to produce conical shaped samples with diameters decreasing from 8 mm to 1 mm. X-ray diffraction and Neutron Diffraction were used to characterize the alloys with the aim of obtaining the critical glassy diameter, dc, of the alloys. The results showed the composition with the biggest dc was the Cu61.48Hf18.52Zr6.48Ti13.52 alloy, with dc = 6 mm. Thermal parameters were obtained by differential scanning calorimetry and the maximum values for glass transition temperature, Tg, (747 K), crystallization temperature, Tx, (772 K), solidus temperature, Tm, (1152 K) and liquidus temperature, Tl, (1230 K) corresponded to the Cu61.48Hf18.52Zr6.48Ti13.52 composition. The results also showed that the parameters obtained from thermal analysis did not correlate with the GFA obtained. However, a good correlation of GFA and dc was found by means of the topological model, where the highest % packing efficiency (53.57 %) was found for the Cu61.48Hf18.52Zr6.48Ti13.52 alloy, which also showed the highest dc value with 6 mm.

Resumo em Inglês:

The waste from the processing of kaolin in the Amazonian region of Brazil was subjected to a calcination process at 700°C for 2 h to obtain metakaolin, which, together with sodium hydroxide and sodium silicate, formed the reaction mixture. This mixture was subjected to an aging step (24 h at 60 rpm), and a subsequent hydrothermal process at 110°C for 10 h. By means of X-ray diffraction (XRD), differential thermal and thermogravimetric analysis (DTA/TG) and scanning electron microscopy (SEM) techniques, the crystallization of a single phase, faujasite (FAU) zeolite, was observed. In the postsynthesis process, it was verified by means of XRD that the thermal stability of this structure persists up to a temperature of 600°C. At 800°C, the structure of FAU collapses. Beginning at 850°C, new nepheline phases are formed, and at 1000°C, nepheline and mullite phases are formed.