Resumo em Inglês:

High chromium cast irons (HCCIs) are widely applied in the mining industry as components of equipment for iron ore transportation, in which their surfaces are subjected to abrasive and erosive wear. The present work evaluated the erosion-abrasion behavior of a HCCI possessing different amounts of austenite and martensite, using a laboratory impeller-tumbler wear test apparatus and iron ore pellets as abrasive material. The results showed that the wear dominant mechanism on the worn surface of the as-cast material depends upon the material microstructure. For HCCI destabilized at 930 and 990 °C, the matrix has high martensite/austenite ratio and finely dispersed secondary carbides, offering high abrasion-erosion wear resistance. The absence of fractured eutectic carbides indicates that such matrix has hardness and load bearing capacity, enough for mitigating a significant plastic deformation during the impact pellets. For HCCI destabilized at 1050 °C, the matrix has a low martensite/austenite ratio and coalesced secondary carbides, leading to high wear rates during erosion-abrasion tests.

Resumo em Inglês:

In the present work, synthetic slags (FeO-SiO2-CaO-P2O5-Al2O3-TiO2-V2O5 system) mimicking the composition of the slag inclusions of Ipanema were solidified at different cooling rates. FactSage software was used to calculate the slag’s phase equilibria from 500ºC to 1600°C to guide the microstructural characterisation. The samples solidified with slower cooling rates featured wüstite dendrites and a eutectic-like matrix, with intradendritic (Al,V,Ti)-containing iron spinel precipitates in the wüstite. The rapidly solidified slag showed refined wüstite dendrites surrounded by a Fe-O-Si-Ca-containing amorphous single-phase matrix without intradendritic (Al,V,Ti)-containing iron spinel precipitation. The comparison of the calculated phase diagram with the as-cast microstructures showed a few discrepancies. For instance, the FactSage’s database must be updated to consider the simultaneous solubility of Al, V and Ti in the thermodynamic description of the spinel phases, such as FToxid-SP-V, FToxid-SPINA, FToxid-TiSp and (FeO)2(TiO2)(s). Finally, the intradendritic precipitation of (Al,V,Ti)-containing iron spinel phases in the wüstite of the slag inclusions indicated that an Ipanema’s iron artefact was exposed to high service temperatures between 750 and 1050ºC.

Resumo em Inglês:

Double-layer Ni-P coatings with low phosphorus content in the inner layer and high phosphorus content in the outer layer and Ni-Mo-P composite coatings are successfully prepared on the surface of AZ91D magnesium alloy by chemical plating process. The microstructures, friction and corrosion resistance of double-layer Ni-P and Ni-Mo-P coatings are studied in comparison. Meanwhile, the deposition and corrosion resistance mechanism for the coatings are investigated. Results convey that both Ni-P and Ni-Mo-P coatings showcase an amorphous structure. The coating possesses denser and more homogeneous structure with the co-doping of Mo. The micro-indentation hardness (859.7 HV) and friction coefficient (0.58) of Ni-Mo-P coatings show that the ternary alloy coating is firmly bonded to the magnesium alloy substrate. Besides, the Ni-Mo-P coatings demonstrate exceptional wear resistance attributed to Mo co-deposition, fostering grain refinement and facilitating the growth of passivation films.

Resumo em Inglês:

Ferroelectric thin films of 0.2BaTiO3 – 0.8BaZr0.5Ti0.5O3 (BT-BZT) are dielectric materials applied in various sensors, particularly in capacitor manufacturing, due to their excellent electrical properties. This ferroelectric material also has a high dielectric constant value, such that it is suitable for use in Ferroelectric Random Access Memory (FeRAM) and microwaves. Therefore, this study aimed to synthesize thin BT-BZT films with annealing temperature variations of 700 °C, 750 °C, and 800 °C. To achieve this, the sol-gel method was applied to Fluorine Doped Tin Oxide (FTO) substrate, a selected technique for its simplicity and cost-effectiveness. The electrochemical properties were characterized using electrochemical impedance spectroscopy (EIS). The research results show that at a frequency of 100 Hz, the highest dielectric constant obtained was 58975.43 at a temperature of 800 °C. This temperature has the highest resistance compared to other samples. The highest capacitance value is 2.9 µF at a temperature of 700 oC. Therefore, it was concluded that the annealing temperature influenced the dielectric constant and the capacitance values of the capacitor.

Resumo em Inglês:

Membrane technology offers solutions for separation of complex gas mixtures. Therefore, new efficient and durable membranes are required to produce gas permeation modules with high area/volume for CO2 removal from natural gas. This study aims to develop cost-effective zeolite DD3R alumina composite hollow fibers to achieve these process requirements. A porous hollow fiber support from low-cost alumina was prepared via phase inversion followed by thermal treatment. DD3R zeolite seeds were then implanted over the surface of the microporous hollow fibers to form a selective layer by hydrothermal synthesis. The thickness of the selective layer was controlled by the seed concentration, which also affected the crystal intergrowth and competing zeolite phase formation, Sigma-2, which influenced the membrane performance. A reduced-diameter composite DD3R-alumina hollow fiber was obtained with a selectivity of 203 and a CO2 permeance of 5.4 x 10-8 mol m−2 s−1 Pa−1 at a pressure of 2 bar.

Resumo em Inglês:

The integration of Inconel 718 (IN718) and Cold Metal Transfer (CMT) based wire + arc additive manufacturing (WAAM) for wall fabrication with a near-net shape and low buy-to-fly ratio presents a novel and promising approach with potential applications in various industrial sectors, including aerospace and automotive industries. This research aims to investigate the microstructure and mechanical anisotropy of thin-walled IN718 components that were produced using CMT based WAAM, and to compare the properties of as-deposited and heat-treated samples that underwent aerospace (AMS5663) procedures. To characterize the microstructure of the specimens, we employed optical microscopy and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and an element probe microanalyzer (EPMA). Tensile and hardness tests were conducted to evaluate the mechanical properties of the specimens. Our results revealed that the as-deposited samples exhibited a dendritic microstructure with a high degree of segregation, leading to lower mechanical strength than that of the heat-treated specimens. Precipitated heat treatment promoted the precipitation of strengthening phases, such as gamma prime and carbides, improving the mechanical properties. In contrast, the precipitated heat-treated specimens exhibited a more refined microstructure with equiaxed grains and a significantly enhanced mechanical strength. This study provides critical insights into optimizing the material for different applications, leading to the development of more efficient and effective parts.

Resumo em Inglês:

In this work, electrochemical tests were performed to measure hydrogen permeation during free dissolution of carbon steel in the presence of the ionic liquids (ILs) 1-ethyl-3-methylimidazolium acetate [(EMIM)+(Ac)-], 1-ethyl-3-methylimidazolium bromide [(EMIM)+(Br)-], and 1-butyl-3-methylimidazolium tetrafluoroborate [(BMIM)+(BF4)-] in 5.4 mol L-1 HCl aqueous solution. The permeation inhibition efficiencies (IEp (%)) of 5-hydroxy-2-nitromethylene-hexahydropyrimidine (HPY) and a commercial corrosion inhibitor (CCI) were also evaluated. Among the ILs, the (BMIM)+(BF4)- compound presented the highest corrosion and hydrogen permeation inhibition efficiencies, with values of 23% and 30%, respectively. The (EMIM)+(Br)- and (EMIM)+(Ac)- compounds were not effective against corrosion, but they presented IEp of 15.8% and 23%, respectively. The HPY compound demonstrated 61% effectiveness in preventing corrosion, while in silico evaluation indicated no toxicity. However, neither the HPY compound nor the CCI compound inhibited the entry of hydrogen into the carbon steel during the pickling process.

Resumo em Inglês:

The novelty of the present study lies in synthesized ZnO film in a single step by chemical bath deposition. The typical conversion of zinc hydroxide (Zn(OH)2) into ZnO material through thermal annealing is not required. A direct synthesis has achieved using four different zinc salt sources, yielding equivalent results. All the synthesized ZnO films were non-specular and adhered well to the glass slide substrates. We present the results of the structural, optical, and morphological characterization techniques. These revealed a hexagonal structure, a band-gap energy of around 3.2 eV, and a hexagonal nanorod shape for all the synthesized ZnO films.

Resumo em Inglês:

A highly efficient NiFe2O4/TiO2 nanofibrous photocatalyst was prepared by a simultaneous solution blow spinning method. The hybrid fibers were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and magnetometry. The photocatalytic properties were evaluated using Crystal violet (CV) and Congo red (CR) dyes under visible light irradiation. Fibers calcined at 600 ºC and 700 ºC showed the highest CV decolorization (77%). On the other hand, for CR, the best performance was encountered with the photocatalysts heat-treated at 500 ºC, which exhibited photocatalytic degradation of 87% after only 30 min of visible light irradiation. The high reaction rates (0.018 to 0.067 min-1) explain the fast decolorization yielded by the combined effect of adsorption and photocatalytic processes. Moreover, recyclability assays showed stable CR dye efficiency after five recycling cycles. Therefore, the NiFe2O4/TiO2 nanofibers present a high potential for application in the decolorization treatment of wastewater from the textile industry.

Resumo em Inglês:

In most situations, predicting wear requires a variety of microstructural characterizations and experiments with contact surfaces. Based on physical principles, mathematical models might be of great assistance in understanding and thereby predicting this event. Considering the significance of heat generation in war, it appears that the parameters of thermodynamics are appropriate measurements for wear modelling. Entropy is among these parameters of thermodynamics. The Miedema model is a good method to predict the Gibbs free energy and entropy of solid solutions of binary and ternary systems. In this study, the wear behaviour of iron-based alloys according to their estimating values of Gibbs free energies and entropy was studied under lubricated conditions. The wear test was performed in accordance with ASTM-G99, utilizing the vertical universal friction testing machine MMW-1A and the pin-on-disk test methodology. Results show that the lowest negative value of Gibbs free energy was noted in the Fe-Al-Sn ternary system (-14.37 KJ/mol), while the highest negative value was found in the Fe-Al-V (-25.16 KJ/mol) binary system. It was also concluded that the wear rate decreased when the entropy estimate increased. The higher value of the wear rate was (6.935 mm3\N.m x107) for Fe-Al binary alloy with an entropy value (1.717 J\k Mole). The lowest value of wear rate was (3.581 mm3\N.m *107) for Fe-Al-Sn ternary alloy with an entropy of (2.71 J\k Mole). This is due to the micro-distortion that was mechanically indicated with the ternary alloys Fe-Al with V, Mn, Ga.B, and Sn additives that affected the wear mechanism and caused high values of wear.

Resumo em Inglês:

This study assessed the morphology and thermal, mechanical, and chemical properties of electrospun membranes made of acrylonitrile-methacrylic acid copolymers (PANCMAA). Copolymers were synthesized using the aqueous suspension method with varying comonomer contents (homopolymer,PAN, lower acid, PANCMAA1, and higher acid, PANCMAA2) and characterized by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). Electrospun fibers were produced by adjusting the polymer concentration in the DMF solution, and the optimal conditions yielded nanofibrous membranes. PAN and PANCMAA membrane properties were evaluated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMTA), stress-strain tests, and swelling behavior in a phosphate buffer solution. The comonomer content influenced the crystallinity of the electrospun nanofibers, reducing the 16.8° XRD peak intensity from PAN to PANCMAA2. DSC indicated an increased Tg (from 113°C in PAN to 127°C in PANCMAA2) and a decreased exothermic cyclization enthalpy (311 J.mg-1 in PAN to 271 J.mg-1 in PANCMAA2). PANCMAA1 exhibited higher stiffness than PANCMAA2 and PAN, with a storage modulus of 0.16 GPa, a Young’s modulus of 135.7 MPa, and a lower elongation at break (3.98%). The presence of the acid comonomer significantly enhanced the swelling behavior of the electrospun membranes in phosphate buffer solution.

Resumo em Inglês:

It is particularly important to investigate the mechanical performance of carbon fiber (CF) reinforced polyamide 6 (PA6) composites used for automotive and aerospace applications, where diffused moisture of the environment may potentially weaken the material over time. In this work, CF/PA6 composites were subjected to two different types of conditioning: distilled water at a temperature of 80 ºC and saline solution for 12 weeks. The volumetric fraction of CF, PA6 matrix, and the voids of the CF/PA6 composites were determined by acid digestion analysis. At the end of the environmental conditionings, the moisture absorption content and the diffusion coefficient (D) were determined. The mechanical performance of CF/PA6 composites unconditioned and conditioned was evaluated through tensile and interlaminar shear strength (ILSS) tests, and morphological characteristics of the fracture surface after the mechanical tensile test. CF/PA6 composites conditioned in saline solution showed a decrease of 53% (tensile sample) and 72% (ILSS sample) in the diffusion coefficient (D) and insignificant losses of mechanical properties when compared to CF/PA6 composites conditioned in distilled water at 80 ºC. This behavior is attributed to the salt molecules blocking the pores and consequently reducing the migration of water into the samples, maintaining the internal integrity of the specimens.

Resumo em Inglês:

Ni0.5Co0.5Fe2O4 nanoparticulate powders were synthesized using coprecipitation and sol-gel methods. The crystalline structure of the nanocompounds was determined through X-ray diffraction analysis. The chemical composition of the synthesized nanopowders was analyzed using infrared spectroscopy measurements. The size, morphology, and aggregation of the nanoparticles were determined from electron microscopy images. The magnetic properties of the nanocompounds were studied through magnetization measurements as a function of temperature and applied magnetic field. The synthesized powders consist of aggregates of nanoparticles with mean particle sizes of 24 nm and 43 nm, with those synthesized using the coprecipitation method being smaller. The compounds exhibited a single crystalline phase corresponding to the cubic spinel structure, with a unit cell parameter of approximately 8.35 Å and an inversion parameter with values of 0.94 and 0.95. The synthesized Ni-Co mixed ferrites presented an ordered magnetic behavior below 320 K, with the nanoparticles being in the blocked magnetic regime.

Resumo em Inglês:

Reports on freeze-cast ceramic materials frequently focus on the study of the organized macroporosity and the properties of the materials. This study aims to describe the microstructure evolution of freeze-cast alumina during the sintering process, analyzing grain growth, densification, pore elimination and crystal structure at different sintering temperatures (1300-1500 °C). Aqueous suspensions with 20 vol% alumina were freeze-cast in liquid N2 and sintered. The microstructure was analyzed by stereological analysis, N2 adsorption and X-ray diffraction. Grain sizes varied within 237-500 nm, and the intergranular porosity decreased from 8.8% at 1300 °C to 1.4% at 1500 °C. N2 isotherm analysis revealed pore shrinking from the region of macro and mesopores (20-80 nm), to smaller residual mesopores (3.7-15 nm) at temperatures above 1400 °C. Rietveld refinement of the XRD diffractograms confirmed increased crystallite size and decreased lattice strain at higher sintering temperatures. This comprehensive description of microstructural evolution of the freeze-cast alumina contributes to understanding the sintering of highly porous ceramics produced via freeze-casting.

Resumo em Inglês:

The developed novel Nanoclay (NC) filled bamboo fibre (BF) /glass fibre (GF) reinforced unsaturated polyester (USP) hybrid composites were subjected to static and dynamic mechanical studies. Effect of NC on mechanical properties of the neat and NC filled BF/GF hybrid composites were tested in accordance with the ASTM standards. Dynamic mechanical analysis was performed on the composites to evaluate their viscoelastic properties like, storage modulus (E’), loss modulus (E”) and damping factor (Tanδ). Outcomes of the mechanical results revealed that, NC filled BF/GF-USP hybrid composites showed superior mechanical performance over the neat hybrid composites particularly 5 wt.% NC filled BF/GF hybrid composite (HC4) outperformed other composites. From the dynamic mechanical it was found that the addition of NC filler in the hybrid composites enhanced the E’, E” and glass transition temperature (Tg). Fractured specimens of the hybrid composites were examined using Field emission electron microscope (FESEM). Matrix fracture, micro-cracks, fibre pullouts, stretching of fibres and delamination of the fibre layers were significantly noted in the fractography analysis. Therefore, from the obtained results, NC filled BF/GF USP hybrid nanocomposites can be employed for automotive applications.

Resumo em Inglês:

Nitrocarburized coating by plasma electrolytic saturation, PEN/C coatings, have been proposed to increase the corrosion and wear resistance of steel by using a process of low-temperature hydrostatic plasma. The objective of this work is to analyse the wear and corrosion resistance of PEN/C coatings on SAE 1045 steel, using the electrochemical slurry erosion wear test (ESEWT). This test allows the evaluation of the simultaneous effect of erosion wear and electrochemical behaviour on this coating. Thus, it was possible to evaluate the erosive and corrosive effect and the synergy of these phenomena on the PEN/C coated SAE 1045 mass loss rates. ESEWT tests were performed at different times and under different electrochemical conditions: under cathodic protection and open circuit potential (OCP). The PEN/C coating increased the corrosion resistance of SAE 1045. Synergy between the erosive wear and corrosion was the main factor in the mass loss rates of both analysed systems. The synergistic mechanism of the substrate occurred by removing the corrosion product and by activating the surface generated by the erosive process of the particles. The synergistic mechanism of the PEN/C coating occurred with the removal of inherent surface irregularities through the erosive process, combined with localized corrosion.

Resumo em Inglês:

Powder metallurgy is an attractive method for cost effective production of near net shape Ti-Nb alloys, and, when elemental powders and coarse HDH powders are used, a higher flexibility in alloy composition and low processing costs can be achieved. In this study, manufacturing of (α+β) Ti-Nb alloys by powder metallurgical techniques using coarse HDH Nb (D50= 110 μm and D50= 255 μm) and HDH Ti (D50= 22.6 μm) powders as starting materials was described. Tape casting was applied for the production of porous sheets while warm compaction of Metal Injection Molding (MIM) feedstock was applied for the production of dense parts. Microstructural and mechanical tests were employed to investigated the effect of coarse Nb powders on the sintering behavior and mechanical properties. Tape casting enabled to produce porous sheets of Ti16Nb alloy with an interconnected porosity varying from 14 - 31 vol.%. Warm compaction enabled to produce Ti-Nb parts with less than 2% porosity and Yield strength in compression of 975-1100 MPa, which is similar to the values reported for Ti-Nb based alloys produced by powder metallurgy of finer powders. A dynamic Young’s Modulus of 37-52 GPa, significantly lower than that of cp-Ti was achieved. These results might provide guidelines for the use of coarse Nb powders as starting materials for the powder metallurgical development of low-cost Ti-Nb based alloys.

Resumo em Inglês:

Ti alloys have been developing through the years, aiming the biomedical application since it has suitable properties. Among Ti alloys, the Ti-Nb systems are a pronounced group to biomedical applications due to its low elastic modulus, good corrosion resistance, and mechanical properties. Although this system is quite well-known regarding its phases, structure and properties, there is not plenty of information about wear available in the literature. To investigate the wear resistance, the samples were submitted to x-ray diffraction (XRD) and scanning electron microscopy (SEM) to analyze the phases formed. Hardness and elastic modulus were measured by microhardness Vickers and dynamic Young modulus by excitation impulse. Additionally, wear volume, wear resistance, and H/E ratio were calculated to understand the wear material’s performance. This study aims to investigate the wear resistance of Ti-xNb (x = 15, 25 and 40wt.%), one of each type of Ti alloys and phases formed: Ti-15Nb (α´), Ti-25Nb (α”) and Ti-40Nb (β) and the influence of cooling rate after solution heat treatment on wear properties through ball cratering. It was possible to find that the harder the alloy, the higher the wear resistance. Thus, in the case of Ti-xNb (x = 15, 25 and 40wt.%), alloys the hardness plays a significant role in wear resistance. Besides that, the samples that have presented the α´ or α”phase have the lowest wear resistance. Therefore, not only the hardness influences the wear resistance but also the combination of phases formed.

Resumo em Inglês:

In this study, we hypothesized that microtextured titanium (Ti) surfaces produced by laser metal fusion (LMF) 3D printing may play an important role in osteoblastic differentiation of mesenchymal stem cells (MSCs). For that, MSCs derived from mouse bone marrow were cultured on Ti discs produced in two different ways: microtextured produced by acid etched (Ti-Ac, control group) and microtextured produced by LMF 3D printing (Ti-3D-LMF, test group), in which it was evaluated: (1) cell proliferation, (2) alkaline phosphatase activity and (3) extracellular matrix mineralization. The results showed that both groups allowed cell proliferation over time (p<0.001). Additionally, there were no statistically significant differences between groups in the assessments of alkaline phosphatase activity (p=0.385) and extracellular matrix mineralization (p=0.234). Although both groups evaluated induce cell proliferation and osteoblastic differentiation similarly, the technology used in the Ti-3D-LMF group may prove advantageous as it produces specific dental implants for patients through customization.

Resumo em Inglês:

This research investigates optimizing the properties of 2024 aluminum alloy using the Extreme Vertices Design (EVD) method and linear regression. It examines the oxidation behavior of the alloy during solubilization heat treatment, specifically focusing on the effect of magnesium addition leading to a dark oxide layer. The study employs a comprehensive experimental design and regression models to estimate the specific oxidation rate constant (k). Analysis of results reveals variations in oxidation behavior among alloys and the influence of aluminum, copper, and magnesium concentrations on the oxidation rate. The regression analysis yields a comprehensive equation: k = -0.01Al - 4.06Cu - 15.71Mg + 4.52Al·Cu + 17.01Al·Mg + 418.5Cu:Mg - 447.7Al·Cu·Mg, with statistically significant results (p < 0.05) for all terms. An increase in magnesium concentration was found to enhance the oxidation rate, implying a higher alloy susceptibility to oxidation. These findings underline the value of the EVD method and regression analysis in alloy property optimization, thus aiding in the design of aluminum alloys with improved oxidation resistance.

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Additive manufacturing (AM) technology depends on the implemented selective laser melting (SLM) process. A good comprehension of its parameters is required to perform an efficient SLM process. Therefore, this study develops a computational fluid dynamic (CFD) model to simulate the SLM process based on a novel approach (particle by particle) and analyze its operating parameters. The model is based on the classical physics laws to formulate the governing equations and solve them in the ANSYS FLUENT software WORKBENCH R19.1. Melting of stainless steel 316L powder particles was considered a case study where laser power, scanning speed, and spot diameter were considered steady parameters. A User Define Function (UDF) is written in C-language to define the heat source and its parameters, and then it is run over the cell face center in every time step. A parametric study was conducted for three of the SLM main parameters; laser power, spot diameter, and scanning speed. The model was verified through the validation process, which confirmed the model's accuracy and reliability. The model outcomes revealed a proportional relationship between the laser power and each melting temperature and liquid mass fraction for a fixed spot diameter and scanning speed. Moreover, a higher energy density is achieved for a smaller laser spot diameter, which yields a higher liquid fraction and melt temperature.

Resumo em Inglês:

The corrosion behavior of Al0.8CrFeCoNiCu0.5Six (x=0, 0.2, 0.3) high-entropy alloy laser cladding coatings in a 3.5% NaCl solution was investigated using polarization tests, impedance spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy. As the Si content increased, the over-passivation potential and the width of the passivation zone for the Al0.8CrFeCoNiCu0.5Six coating expanded, while the corrosion current density tended to decrease, enhancing the stability of the passivation film and the corrosion resistance of the coating. The Al0.8CrFeCoNiCu0.5 coating underwent selective corrosion, with some pitting corrosion distribution showing no apparent regularity. The Al0.8CrFeCoNiCu0.5Si0.2 coating exhibited a distinct grain profile with a tendency towards intergranular corrosion. The aggregation of Cu-rich and Al-Ni intergranular phases in the eutectic structure led to preferential erosion at the grain boundaries by corrosion ions in the Al0.8CrFeCoNiCu0.5Si0.2 coating. The Al0.8CrFeCoNiCu0.5Si0.3 coating presented corrosion pits, although their distribution did not display apparent regularity. The Al0.8CrFeCoNiCu0.5Six high-entropy alloy coating demonstrates superior corrosion resistance in solution compared to 5083 aluminum alloy.

Resumo em Inglês:

This study synthesized mixed matrix membranes (MMMs) using PEBAX® MH-1657 and ZIF-67 with varying particle concentrations (1, 3, and 5 wt%) to assess permeability and selectivity. ZIF-67 nanoparticles were prepared using the solvothermal method with methanol and characterized. Permeation tests were conducted at 10 and 15 bar using N2 and CO2. The analysis revealed ZIF-67 particles with an approximate diameter of 280 nm and confirmed characteristic sodalite peaks. The ideal CO2/N2 selectivity reached 67 (CO2 permeability = 132 ± 3.5 Barrer) at 15 bar. The impact of ZIF-67 varied with pressure and composition; at 10 bar, CO2/N2 selectivity decreased compared to pure PEBAX®; however, at 15 bar, the 1 wt% ZIF-67 membrane exhibited superior selectivity, surpassing Robeson's upper bound. The results indicate that ZIF-67 enhances the permeability and selectivity of PEBAX®, with superior performance observed at lower concentrations.

Resumo em Inglês:

Biocomposites have gained attention in the packaging industry due to their potential as sustainable alternatives to conventional synthetic materials. In this study, novel cotton incorporated poly(lactic acid)/thermoplastic starch biocomposites were developed for packaging applications using in short shelf life products the extrusion method. Pelletized samples obtained by extrusion were stamped from plates obtained by compression and were characterized through measurement of density, hardness, contact angle and water absorption, as well as Fourier transform infrared spectroscopy (FTIR), thermal analysis and scanning electron microscopy (SEM). No significant changes in the density results were observed. A slight increase in the hardness of formulations in relation to the PLA was associated with the presence of cotton fiber in biocomposites. The FTIR results revealed physical interaction of PLA, TPS and cotton fiber. By DSC analysis, for all formulations the melting exhibited only one peak, suggesting good homogeneity and interaction among the components, as observed by TG/DTG results, and corroborating SEM analysis. The biocomposite PLA/TPS/Cotton 85/10/5 wt.% displayed greater increase in water absorption than both 95/5/0 and 90/5/5 wt.% formulations, which can be attributed to the increase in starch proportion, confirming the contact angle results. The hydrophilic tendency corroborated the biodegradation process in the packaging end-of-life.

Resumo em Inglês:

A novel, efficient, and cost-effective coating method was developed for fabricating highly conductive cotton yarn loaded with reduced graphene oxide (rGO). This method is straightforward, rapid, scalable, and amenable to solution processing. The key innovation involves pretreating the cotton yarn with chicken egg albumin (CEA) before applying the rGO coating through a simple dip-and-dry process. This method significantly reduces the electrical resistance of the cotton yarn, achieving an optimal specific resistance of 80 Ω.g/cm2 with just five coating cycles. Additionally, the coated samples exhibit exceptional reliability, enduring 104 bending tests and 5 washing tests without compromising conductivity. Notably, the study reveals consistent proportional variations in response to changes in relative humidity, regardless of the initial reference resistance value or yarn characteristics. These stable and conductive rGO-coated cotton yarns (rGOCY) might be seamlessly integrated into textiles and garments, enabling the development of flexible and wearable electronics, as well as sensors.

Resumo em Inglês:

Blending finer powders of Ti, Zr, Ta, Sc, and Nb compounds as inoculants have been a promising strategy to modify precipitation-hardened aluminum alloys for laser-based powder bed fusion, promoting a crack-free equiaxed microstructure. However, there is still a lack of comprehensive understanding of the influence of these fine Al-Nb-B inoculant particles on the AA 2017 powder's physical characteristics and flowability during the process. The results indicate that blended powder has a similar PSD to AA 2017 powder. Furthermore, the circularity, smoothness, and morphology of the particles indicate that both inoculant and AA2017 powders do not exhibit high sphericity, but the blended powder showed slightly more agglomerated particles. Regarding rheological properties, it was observed that a higher flow energy was required to move the blended powder in unconfined conditions compared to the AA 2017 powder. Additionally, the blended powder exhibited higher compressibility and tendency to retain air in packed conditions during the deposition and spreading process. In conclusion, the physical characterization techniques combined with rheological tests have proven to be a rapid and reliable approach for assessing the impact of the finer inoculant particles' characteristics on the laser-based powder bed fusion.

Resumo em Inglês:

The accumulation of tramp impurities, particularly Fe, during recycling of Al alloys frequently leads to the production of coarse intermetallics during solidification, which affect final product mechanical properties. Because lowering the Fe concentration and/or using thermomechanical processing to subdivide the particles is expensive, it is preferred to modify the morphology, size, and distribution of the IMCs during solidification. Benefiting the properties of Al-contaminated alloys entails increased recyclability and a reduction in the usage of virgin primary Al and downcycled alloys. The Al-8%Si-0.8%Fe-2.5%Cu-1.0%Zn (in wt.%) alloy was modified with 0.7%Ni and 0.7%Co. Both dendritic growth and tensile properties were evaluated for the three alloys. The secondary dendrite arm spacing values (λ2) were found very refined for all alloys. The λ2 in the modified alloys was even more reduced. The Co addition of 0.7% reached higher values of tensile strength (220 MPa) as compared to the others without major losses in ductility. The addition of Co can enhance strength by up to 15%, considering more refined microstructures.

Resumo em Inglês:

Austenitic and lean duplex stainless steels, such as AISI 317L and SAF 2304, present high mechanical and corrosion resistance, which make them alternative materials for biodiesel plant equipment. Because there is not sufficient research about these stainless steel-specific applications, this work aims to evaluate AISI 317L and SAF 2304 stainless-steel pitting corrosion resistance in a chloride-containing acidified glycerin solution, collected directly from a biodiesel plant. The SAF 2304 presented a higher pitting potential than the AISI 317L, at room temperature and at service temperature, 337 K. However, the SAF 2304 passive layer was more reactive than the AISI 317L, showing a higher passive current density in the polarization and chronoamperimetric tests. Furthermore, the Mott–Schottky technique showed that the passive layer of the AISI 317L steel contained a lower concentration of defects than the passive layer of the SAF 2304, and the oxides of the passive layers are n-type semiconductors.

Resumo em Inglês:

The surge in deep and ultra-deep water oil exploration in Brazil, particularly in the pre-salt layer, necessitates the advancement of materials and engineering components to meet sectoral challenges. To enhance the longevity and corrosion resistance of pipelines and structures, welded cladding of stainless alloys onto structural steels has been deployed. However, dissimilar welding often leads to the formation of Partially Diluted Zones (PDZ), marked by discontinuous, high-hardness regions at the interface. This study employs Electron Microscopy via Backscattered Electron Diffraction (EBSD) to characterize these zones, addressing limitations in conventional metallographic techniques. By cladding ASTM A36 steel test plates with AWS E 309L (309L stainless steel) through automated MIG welding, metallurgical-mechanical properties were assessed using Field Emission Scanning Electron Microscopy (FEG-SEM), EBSD, SEM-EDS, and Vickers Microhardness. The Heat-Affected Zone (HAZ) displayed low hardness, while the PDZ exhibited varied morphologies with significant concentrations of iron, chromium, and nickel, accompanied by elevated microhardness and a characteristic martensitic microstructure. In comparison between single and double-layer depositions, the latter substantially reduced hardness in the PDZ and HAZ. This study provides critical insights into the microstructural attributes of welded cladding, offering valuable guidance for optimizing materials in deepwater applications.

Resumo em Inglês:

A solution blow spinning (SBS) process was utilized to create nanofibers of TiO2/C and TiO2/C/N with potential applications in photocatalysis and dye adsorption. Polyvinylpyrrolidone was used as a carbon and nitrogen source. Their content in the TiO2 structure decreased as the temperature increased from 350 to 550 °C. Physical-chemical, morphological, and structural features were investigated. Adsorption and photodegradation experiments revealed that the material calcined at 400 °C had higher dye removal (98%) under dark settings, whereas the greater photodegradation efficiency under visible and UV light was 56% and 98%, respectively, for the sample calcined at 550 °C. The results suggest that the SBS has the potential to develop an efficient adsorbent and photocatalyst for use in treatments of contaminated water.

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This study used an aqueous dispersion of silanized colloidal silica (SCS), whose particles’ surfaces were modified with an epoxysilane-based coupling agent, as the liquid medium and binder for MgO-Al2O3-containing suspensions. Fine calcined alumina and magnesia sinter particles were dispersed in SCS to form a 65 vol% solids suspension. Equivalent silica-free compositions containing calcium aluminate cement or unsilanized colloidal silica were tested as references. After mixing, the SCS-suspension showed low viscosity and suitable workability and, after curing, a thin protective coating of magnesium silicate hydrate (MSH) was formed, thus preventing MgO hydroxylation and improving bonding strength, generating green-dried structures of significant flexural strength (8 MPa). During initial heating, the decomposition of MSH and the softening of amorphous silica particles reduced the overall expansion of spinel (MgAl2O4) formation. After sintering at 1600ºC, the structure showed intense densification (total porosity of 8%) high flexural strength (73 MPa) and large spinel crystals surrounded by a thin layer of amorphous silica and magnesium silicates.

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This study investigated the impact of adding graphene oxide (GO) and iron oxide (II) (Fe3O4) nanoparticles individually and in combination on the morphology, thermo-mechanical, and dielectric properties of a Polypropylene/High-Density Polyethylene (PP/HDPE) blend. By adding these nanoparticles separately or as a mixture, we can determine if both mechanisms have a synergistic effect and how they impact the dielectric constant values of their nanocomposites. The nanoparticle mixture was prepared in both an alkaline and a neutral medium. The mixture in the alkaline medium contained lower quantities of iron nanoparticles than in the neutral medium, and they were localized on the surface of GO. The nanocomposites showed significant differences in dynamic-mechanical and dielectric properties. The system with Fe3O4 exhibited a higher storage modulus, while the system with GO had a higher dielectric constant. However, no synergistic effect was observed in the nanoparticle mixtures.

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In this study, nanostructured coatings of VN2/Fe3N/Fe4N are synthesized by Plasma Deposition (CCPD) using a vanadium cathodic cage and subject to cathodic and floating potential treatments. Microstructural and mechanical properties of coated SAE 1080 steel samples are investigated using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Vickers microhardness (HV), and surface roughness analysis. The coating produced under cathodic potential treatment exhibited a nitride-based microstructure (VN2, Fe3N, Fe4N), with surface morphology consisting of clusters of granular structures with varied particle sizes. The coating produced under floating potential predominantly exhibited the iron nitride phase (Fe3N) with a morphology composed of uniformly sized grains. Microhardness testing showed that both layers exhibited more excellent plastic deformation resistance than the substrate. Roughness measurements confirmed a more organized microstructure profile for the sample treated under floating potential. This study demonstrates that the CCPD-produced cathodic potential coating can be utilized in tribological applications.

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Alzheimer's disease (AD) is the most common cause of dementia worldwide. Fifty million people today are affected by this disease globally. AD has had a tremendous impact on the affected individual, caregiver, and society, in both developed and developing nations. Donepezil—chitosan-gold nanocomposite (Donz-CS-AuNPs) was prepared by co-precipitation technique. Placket-Burman experimental design was used in this work to estimate the effect of the three independent variables (concentration of chitosan, gold, and donepezil) on the dependent variables (loading efficiency, and particle size) by using Minitab 18.1 software. The quantities for the independent variables used were: 10 and 40 mg of donepezil, 24.6 and 73.8 mg of gold, and 500 and 1500 mg of chitosan. The Donz-CS-AuNPs were characterized using energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and release study. The results of EDX showed strong signals of Au (1.5–2, 2–2.5 and 9.5–10 keV), which confirmed the specific gold peaks from the Donz-CS-AuNPs. The XRD pattern of Donz-CS-AuNPs nanocomposites showed the existence of AuNPs peak at 2θ= 38.2°, 43.8° and 64.5°. The SEM images demonstrated spherical shapes of the AuNPs. In the in vitro release study, the release increased steeply and reached 75% after 1440 min.

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A device with a controllable atmosphere has been designed and fabricated to sinter metal particles in the manufacturing processes of metallic components (porous or non-porous parts). The device avoids the employment of an expensive controlled atmosphere furnace (a furnace in which it is possible to produce a vacuum or through which a constant flow of highly pure inert gas is maintained to protect the specimen). Metallic powders of pure metals or alloys with sintering temperatures (Ts) up to 1300°C and different forms and particle sizes can be used. The device consists of two chambers (an upper chamber for the atmosphere control and a lower chamber for the sintering processes) which are coupled by a sealed system composed of an O–ring and a clamp. The device is designed to be utilized with any conventional vertical electrical furnace (a furnace without the possibility of producing a vacuum inside or maintaining a constant flow of inert gas inside) and can be operated in three different ways: i) with a vacuum inside, ii) with a static atmosphere of inert gas inside, and iii) with a dynamic atmosphere of inert gas inside.

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The aim of this paper was to analyze the passivation of the rear face of silicon solar cells by TiO2 thin films produced by atmospheric pressure chemical vapor deposition (APCVD). A compact high-throughput APCVD system was employed to deposit the TiO2 films. Silicon solar cells with a n+pp+ PERT (passivated emitter rear totally-diffused) structure were produced and characterized. The use of TiO2 on the rear face resulted in a 0.5 mA/cm2 increase in short-circuit current density and a 0.5% absolute improvement in efficiency compared to devices without a passivation layer. Analyzing the internal quantum efficiency of the devices, we concluded that this economically technique provides passivation on the p+ surface, doped with boron, similar to that obtained with thermally grown silicon oxide films.

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The demand for oil and its derivatives has driven the oil and gas sector to explore deep waters. Nickel-based alloys, like Inconel, are used due to their corrosion resistance properties. Cladding structural steels with these alloys is a cost-effective solution. However, dissimilar metal welding poses challenges, including the formation of Partially Diluted Zones (PDZ). This work highlights the use of Electron Backscatter Diffraction (EBSD) as a very adequate technique for the microstructural characterization of dissimilar anticorrosive materials. The MIG process was utilized to perform cladding of Inconel 625 onto the A36 steel substrate. The samples were prepared for analysis using techniques such as EDS, FEG-SEM, EBSD, and Vickers microhardness testing. The results demonstrate the effectiveness of the EBSD technique in characterizing dissimilar metal cladding. The combination of EBSD with EDS analysis and microhardness testing provided comprehensive insights into the microstructure and mechanical properties of the material. EDS mapping analysis confirmed the formation of PDZ with a distinct beach-like morphology, indicating localized compositional variations. The uniform thickness of the PDZ, approximately 20 µm, highlights the convective motion and solidification behavior of the partially diluted zone. Phase map EBSD analysis revealed different crystal structures in the cladding zone, including a FCC structure for the nickel cladding layer and a BCC structure for the ferritic steel base metal. The PDZ exhibited the same crystal structure as the base metal, indicating chemical element diffusion without altering the ferritic steel structure. Contrast band EBSD analysis provided detailed microstructural information, revealing solidification structures and potential hardness variations. The observed martensite formation in the PDZ highlights its susceptibility to cracking and detachment of the coated layer. The hardness results support the microstructural findings, demonstrating significant variations in hardness across the cladding structure, particularly in the PDZ and at the interface between the Inconel alloy and the base metal. These findings contribute valuable insights into the microstructural and compositional gradients within the joint region, reinforcing their implications for material performance.

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Electrospinning, an economical technique, is widely used for biomedical scaffold fabrication, crucial in tissue and organ regeneration, particularly with biomaterials. Polymers, either pure or reinforced with ceramics, aid in cell proliferation and tissue formation. Polyhydroxybutyrate (PHB) is a promising biopolymer for tissue engineering, offering biocompatibility comparable to petroleum-derived polymers. Combining PHB with hydroxyapatite (HAp) enhances mechanical strength and osteoconductivity. This study aims to produce electrospun PHB microfibrous webs reinforced with HAp for scaffold fabrication. Morphological variations are analyzed through manipulation of electrospinning parameters. The study observed microfibrous webs with diameters ranging from 2 to 9 µm. Mechanical and microstructural evaluations demonstrate superior strength of PHB/HAp microfibrous webs compared to pure PHB, 1.23 MPa and 0.58 MPa respectively, demonstrating the efficacy of HAp reinforcement. These findings highlight the potential of PHB/HAp microfibrous webs in bone tissue engineering.

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Magnesium stannate (Mg2SnO4) samples with 0.003, 0.004, 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.5, 1, 2, and 5 at. mol% of Co2+ were prepared by wet chemical method. The samples were investigated using X-Ray diffraction and photoluminescence techniques at room temperature. The results indicate that Co2+ occupies tetrahedral sites in the inverse spinel structure of Mg2SnO4, replacing Mg2+. The material exhibited a red-infrared luminescence associated with Co2+ spin-allowed transitions. Crystal field parameters were calculated using Tanabe-Sugano theory for d7 systems in tetrahedral environment. In the range studied, optimum divalent cobalt concentration for emission applications was found to be 0.08 at. mol%.

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This research investigates the effects of accelerated spheroidizing of cementite on the mechanical properties and microstructural characteristics of commercial steel grades (Fe-0.2C, Fe-0.5C, Fe-0.7C wt%), emphasizing the role of cold-rolling reduction followed by stress relief annealing. Utilizing SEM imaging, X-ray diffraction, and EBSD measurements, this study comprehensively examines how variations in carbon content influence hardness, dislocation density, and crystallographic texture orientation. Microhardness measurements reveal a direct relationship with carbon content, yielding values of 28.0±1.0 HRC for DT-1020, 36.0±1.0 HRC for DT-1050, and 39.0±1.0 HRC for DT-1070. Texture analysis through EBSD demonstrates distinct patterns among the grades: DT-1020 displays a dominant (111) texture, DT-1050 exhibits a (101) orientation, and DT-1070 features a more refined (101) texture. Dislocation density analysis further corroborates the impact of carbon content, with DT-1050 presenting the highest density at approximately 7.8×1016 m-2. This detailed exploration elucidates the intricate interplay between carbon content, cementite morphology, and their collective influence on mechanical performance of steel, providing valuable guidance for tailoring steel properties via microstructural control.

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AISI 316L is a metallic biomaterial used in Unified Health System (SUS) due to low cost. However, corrosion in AISI 316L is a major cause of premature failure and toxic reactions to implants. Nanotubular or nanoporous anodized layers have proven to be good and affordable alternatives to create greater interaction and less damage to human tissue. Thus, the main of this study was to obtain a nanoporous layer by anodizing on AISI 316L, aiming to improve its corrosion resistance for use as a biomaterial. AISI 316L were anodized in 10M NaOH, 0.6mA/cm2 for 5 and 10min. Transients of current density and potential and oxide color were evaluated. Anodized layers were characterized by scanning electron microscopy, X-ray diffraction analysis and electrochemical assays. Nanoporous anodized layers with nanoplate arrangement were obtained. The 5min anodized sample showed better corrosion resistance than the original steel, being considered promising for use as a biomaterial.

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A novel tungsten carbide (WC)-reinforced nickel (Ni)-based laser cladding layer was prepared through an in-situ synthesis process. The mechanism of the effect of scanning rates and laser power on the microstructures, wear and corrosion resistance of in-situ synthesized WC-reinforced Ni-based cladding layer were analyzed. The results revealed that the optimal in-situ synthesized WC laser cladding process entailed a scan rate of 3 mm/s and a laser power of 3000 W. The generation of WC phase has a significant strengthening effect on the cladding layer, which exhibits outstanding hardness (1261HV0.2). There is no clear linear relationship between scanning rate and abrasion resistance, and the coating abrasion resistance increased with increasing laser power. Furthermore, increasing the laser power improves the corrosion resistance of the cladding layer, while the scanning speed has a minimal effect on corrosion resistance.

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For decades, lead-acid batteries have been supplying power to electrical systems through redox reactions involving Pb and PbO2. However, the energy supply capacity is inherently constrained by low energy density and challenges associated with charge/discharge cycles. Studies have indicated that additions of C to the composition of the active mass improve the electrochemical properties of batteries. This work aims to produce, characterize the microstructure and evaluate the electrochemical properties of Pb-Carbon composites, comparing different types of C (graphite, graphene and xerogel). The samples were produced through powder metallurgy, pressed at 550 MPa and sintered at 320°C-48 h. The microstructure was characterized by XRD, SEM/EDS, and Vickers microhardness. Electrochemical analyses were evaluated through OCP, polarization, and cyclic voltammetry (CV) measurements in a solution of 4.91 mol•L-1 of H2SO4. Microstructural characterizations revealed dispersions of C particles in the Pb matrix and an increase in the microhardness of the composites. Electrochemical analyses showed an increase in polarization resistance and a reduction in the corrosion rate compared to Pb. CV curves, demonstrated that C particles enhanced electrical conductivity for the formation of PbSO4 and PbO2, allowing greater absorption of electrical overpotentials when compared to Pb, thereby improving charge/discharge cycles in positive grids.

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AISI 420 steel samples were subjected to three heat treatment conditions: annealed, hardened, and tempered at 400°C, followed by low-temperature nitriding using N2, H2, and varying Ar proportions in a pulsed DC glow discharge. The study aimed to investigate the impact of varying Ar content (10–50 vol.%) on glow discharge characteristics and surface properties of nitrided samples, using an 80% N2 + 20% H2 base gas mixture. The samples underwent characterization including optical microscopy, X-ray diffractometry, microhardness, and roughness measurements. Plasma characterization was conducted using optical emission spectroscopy. The results indicated that higher Ar concentrations led to increased thickness of the nitrided layer (up to 67%), as well as hardness (up to 14%) and surface roughness (up to 50%). These improvements stemmed from increased Ar-based species bombardment on the surface, enhancing the cleaning effect of surface oxides. This facilitated nitrogen adsorption onto the steel surface, increasing the atomic nitrogen concentration in the outermost layer of the steel. The increased nitrogen concentration facilitated diffusion, resulting in significant physical-chemical reactions at the surface-plasma interface. These reactions, including sputtering, molecule dissociation, and recombination, led to enhanced high-diffusivity pathways within the martensitic microstructures of both the as-hardened and 400°C-tempered samples.

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Reconstruction of random heterogeneous media has been an increasingly popular theme in materials science, as such media is primarily found in nature and manufactured materials. An ideal reconstruction includes every microstructural feature of the reference image and allows simulations of physical quantities that agree with experimental data. In this work, three 2D reconstructions and three 3D reconstructions are produced. All six are based on a single planar section. Its stereological and metallographic features are compared to those of the reference. 2D and 3D reconstructions from single planar sections were carried out with simulated annealing and a sampling method. The first reconstruction used the co-occurrence correlation function (CCF) and orthogonal sampling. The second employed the two-point correlation function (S2) and the lattice point algorithm (LPA) as the sampling method. Finally, the third reconstruction used the S2 together with the two-point cluster function (C2) and the LPA as the sampling method. One of two sampling techniques (orthogonal and LPA) were used. The reconstructions that were done using S2 and C2 and LPA sampling provided the best results both in 2D and 3D cases, combining realistic morphology and good compatibility with the reference stereological measures.

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This study explores the behavior of aluminum powder in laser powder bed fusion (LPBF) for additive manufacturing. Focusing on AlSi10Mg powders, the research investigates the effects of environmental conditions, such as temperature and humidity, on crucial properties like moisture content, fluidity, density, and agglomeration. Comprehensive tests, including particle size analysis and fluidity assessments, were conducted. Results showed increased flow time in the Carney funnel fluidity test after storage, but flow properties were maintained under high-temperature, low-humidity conditions. High humidity led to recurrent agglomerate formation. Moisture content analysis aligned with literature findings. Conclusively, these tests provide a reference for material acceptance and aid in supplier comparison for improved machine fluidity. While temperature and humidity impact aluminum oxide formation, humidity's greater relevance affects powder fluidity and quality. Other factors mentioned may cause permanent damage to the aluminum powder.

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In this work, the effects of thermal solidification and microstructural parameters, such as solidification rate (VL), cooling rate (TR), and secondary dendritic spacing (λ2), were studied on the electrochemical parameters of corrosion potential (ECORR), current corrosion resistance (ICORR), and polarization resistance (RP). The alloys were solidified in a horizontal solidification device and two as-cast samples from the heat transfer surface were subjected to electrochemical polarization and impedance techniques. It was verified that the experimental values found for ECORR were relatively close for all the investigated alloys and in both analyzed positions, allowing to deduce that the VL, TR and λ2, as well as the Nb content had little influence, but enough to lead to different behavior in the ICORR and RP. For the alloy with 0.5wt.%Nb, higher VL and TR values, and smaller λ2 resulted in lower ICORR values. On the other hand, for alloys with 3 and 5wt.%Nb, coarser microstructures (greater λ2) have lower corrosion rates. Microstructural analysis showed that Nb acts as a protective element against corrosive actions in the dendritic matrix.

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In this study, Al-Si-Cu-Mg composites reinforced with Silicon carbide (SiC) particles and/or Carbon nanotubes (CNTs) were fabricated using semi-solid stirring casting technology (SSC). The aim of the study was to investigate the influence of SiC and/or CNTs on the mechanical properties, microstructural evolution, and deformation mechanisms of the Al-Si-Cu-Mg alloy. The findings indicated that the presence of SiC/CNTs in the composite had a significant effect on refining the α-Al phase and altering its grain orientation. Additionally, the results obtained from EBSD and TEM revealed that the microstructure of the Al-Si-Cu-Mg-SiC/CNTs hybrid composite (HAMC) underwent dynamic recrystallization (DRX) and static recrystallization (SRX), resulting in a fine equiaxed recrystallized structure. This process also led to the formation of high-angle grain boundaries (HAGBs) through dislocation rearrangement. The SiC particles were evenly distributed within the matrix, ensuring good interface bonding between SiC and α-Al phases. Moreover, the CNTs reacted with the matrix, resulting in the in-situ formation of the Al4C3 phase at the interface. The addition of SiC/CNTs significantly increased the tensile strength of HAMC at 25°C and 250°C, from 319MPa and 178MPa to 438MPa and 331MPa. Examination of the fracture surface of the hybrid composite unveiled that void formation occurred primarily at the regions surrounding the matrix-particle interface.

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The modification of magnesium alloy through the addition of rare-earth elements improves specific properties of magnesium alloy. However, the evolution mechanisms of rare-earth precipitates during thermal cycles are still unclear, particularly during the welding thermal cycles. Therefore, deep research on the influence mechanisms of rare-earth precipitates on the welded joint is necessary. In this paper, Ce-containing Mg alloy was successfully welded by laser welding. The microstructure of the welded joint was deeply analyzed. As a result, the elemental composition and distribution rules of precipitates within the fusion zone were obtained. In addition, heat treatment was carried out for the welded joint, thus deducing the evolution mechanisms of precipitates within the joint. The corresponding results revealed that typical micron/sub-micron-sized particles, consisting of both conventional and rare-earth intermetallics, are formed and neatly distributed within the fusion zone, demonstrating that the rare-earth particles inside the fusion zone are much smaller in size than that of Mg17Al12. Tensile test results suggest that these tiny particles significantly improved the strength of the fusion zone, promoting the tensile-shear strength of the joint accounting for 76.6% of that of the base metal. The above approach provides a feasible solution for the welding of rare-earth Mg alloys.

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CaZrO3and SrZrO3powders were prepared by sol-gel synthesis and plasma sprayed over the Inconel 718 substrate,forming a wear-resistant ceramic coating. X-Ray Diffraction (XRD) analysis of synthesized ceramic powders revealed the presence of CaZrO3and SrZrO3 phases, having an orthorhombic structure. CaZrO3 and SrZrO3powders were sprayed onto the surface of Inconel 718using a plasma spraying process. Scanning Electron Microscope (SEM)analysis of CaZrO3and SrZrO3coated samplesshowedanaveragethickness of about 400μm.Wear depth and wear mechanism for the above sampleswerestudiedusing Pin-on-disc apparatus. Wear results of CaZrO3 and SrZrO3 coated substrates revealed that high wear depths were observed at high speeds and loads. SEM investigations of worn-out samples revealed that both CaZrO3 and SrZrO3 coated samples had undergone delamination wear. CaZrO3 coated samples had exhibitedless delamination and wear depth than SrZrO3 coated samples, thus showing relatively better wear resistance.

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Severe Plastic Deformation (SPD) of metals leads to their strengthening and losses in the work hardening capacity. The latter causes flow localization upon subsequent forming of the material. The application of Low Strain Amplitude Multi-Directional Forging (LSA-MDF) after SPD regenerates the material work hardening capacity and available results cover 4LSA-MDF cycles after 1 and 4ECAP (Equal Channel Angular Pressing) passes in aluminum; the effect of more LSA-MDF cycles after ECAP is not known. This paper presents results for the application of 8, 12 and 16LSA-MDF cycles after 4ECAP passes in aluminum, which led to further work hardening capacity regeneration of the material. The corresponding microstructural evolution involved an increase and stabilization of the HAGBs fraction and increases in the 5-15º boundary disorientation fraction. Monotonic compression after ECAP+LSA-MDF exhibited almost linear work hardening rates, connected to decreases in the HAGBs fraction and increases in the 2-5º boundary disorientation fraction.

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The reduction kinetics of hematite (Fe2O3) powders was studied using nonequilibrium hydrogen plasma as reducing agent. Reduction experiments were performed in a DC pulsed plasma reactor, hydrogen flow-rate of 300 cm3/min, at pressure of 400 Pa, reduction times in range 30-120 minutes and in temperatures range 320-380 °C. Fe2O3 powders after reduction experiments were characterized by X-ray diffraction, weight loss of oxygen (gravimetric analyses), optic microscope and scanning electron microscope. The results showing that the reduction temperature of 380 °C after 120 min allows obtaining α-iron with a reduction fraction of about 0.93. The powder particles are transformed into two steps: Fe2O3→Fe3O4→Fe-α. The activation energy experimentally established for the reduction of Fe2O3 was about 98.4 kJ/mol.

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Mechanical properties may drastically change with temperature, which is crucial to characterize materials in environments as similar as possible to their desired application. This paper discusses a new furnace designed for thermomechanical experiments assisted by Digital Image Correlation (DIC) up to 900°C, with six transparent windows that allow for the visualization and lighting of the specimen. Its versatility is demonstrated in three different experimental configurations, namely, dilatometry, three-point bend experiment, and wedge splitting test. Applied forces and full-field data are used for robust calibration of parameters for numerical simulations.

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Refractory multi-principal element alloys constitute a novel category of metallic materials, and they have good properties, particularly at elevated temperatures. Currently, casting and powder metallurgy stand as the two predominant manufacturing routes. This study focuses on the production of the W19.8Mo19.8Nb19.8Ti19.8Cr19.8Al1 (At. %) alloy via the mechanical alloying process. Analyses of morphology and particle size distribution at intervals of 12, 24, 36, and 48 hours of milling showed a gradual decrease in particle size according to increase in milling time. The XRD showed the presence of the BCC phase after 48 hours of milling, and the application of the Williamson-Hall methods indicated that after 12, 24, and 36 hours of milling, the crystallite size decreased and the microstrain increased gradually. However, after 48 hours of milling, there was an increase in these values, suggesting the reordering of the structure of this alloy. In addition, Fe contamination increases significantly for higher milling time.

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Investigation of corrosion inhibitors on CO2-saturated aqueous solution with O2 contamination is limited. Hence, this study investigated the corrosion behavior of phosphate ester inhibitor towards carbon steel corrosion in a simulated CO2-O2 environment by potentiodynamic polarization technique and electrochemical impedance spectroscopy. It was shown that the PE prevents the corrosion attack in the presence of CO2-O2, reaching an efficiency of 90.7% with 25 ppm in 3.5 wt% NaCl solution at 25 oC. Furthermore, the superficial characterization of carbon steel was studied by scanning electronic microscopy which supported that the inhibitor protects against corrosion. The varying temperatures showed that PE adsorbed on the steel surface by a physical process and obeyed the Langmuir isotherm.

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The existing work is dedicated toward the manufacture of ZA-27/TiC as composites material via powder metallurgy. A mixture of Zn and Al with 63 and 27 wt%, respectively, is ball milled for 4 hrs at 145 rpm. Then, samples with disk-like shapes were made through pressing under 600 MPa and afterward sintered at 336 °C for 90 minutes in an electric furnace in argon gas. Other three groups from the above Zn and Al mixture ratio were prepared but with the addition of 3, 6, and 9 wt% TiC particles independently. The group's samples were prepared at the same conditions above. Hardness, density, and porosity microstructure observations, including optical and SEM-Mapping techniques were utilized to validate the effect of TiC particle additions with the listed above contents on the prepared ZA-27 alloy properties. The practical density of the prepared ZA-27 alloy is decreased basically owing to the used powder metallurgy route and with a lesser degree due to TiC addition. In contrast, the porosity is increased. But the hardness of the ZA-27 alloy is improved when TiC was added, and it was increased from 49.4 to 66 VHN with 0 to 9 wt% TiC addition. The optical microscope and SENM-Mapping facilities explained the distribution of co-existing Zn, Al, and TiC particles in the microstructures of the tested samples to improve the properties of ZA alloy.

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Recent studies have demonstrated mechanical, tribological and corrosion improvements properties on raw materials coated with stainless steel films produced by magnetron sputtering. However, few studies have reported the tribological behavior of thin austenitic stainless-steel films applied to the surface of carbon steels. The present study investigated the tribological behavior of AISI 1045 carbon steel coated with AISI 316 stainless steel film. Pin-on-disc dry sliding wear test was performed. The wear tracks were analyzed using a scanning electron and confocal microscopes. The corrosion resistance of coated and uncoated AISI 1045 were also assessed through an electrochemical test. Samples which presented a mixture of α-Ferrite and γ-iron, with predominant austenite parts, demonstrated lower friction coefficient, lower wear rates, and better corrosion resistance compared to substrate material. The results were also influenced by the variables used in the deposition process, as observed, heating the substrate and submitting to a higher powder density could improve the results. The results found corroborate to the academic and industrial research which looks for coating alternatives to AISI 1045 tools.

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Ferritic stainless steel is essential in many industries due to its corrosion resistance advantages over austenitic stainless steels. However, it is susceptible to embrittlement caused by factors such as grain growth, sigma phase formation, and carbide precipitation. This study investigates the stress corrosion cracking (SCC) behavior of AISI-409 ferritic stainless steel welded with AWS E316LT1-4 flux-cored wire, with heat inputs ranging from 400 J/mm to 805 J/mm. SCC tests were conducted by applying a constant load, followed by mechanical and microstructural analysis upon failure. Interestingly, higher heat input exhibited superior SCC resistance despite slower cooling rates compared to lower heat input. SCC initiated in the heat-affected zone (HAZ) and extended into the ferritic region. Photomicrographs depicted a ductile-to-brittle transition with reduced elongation values. Two distinct fracture regions were observed: dimples and cleavage facets, indicative of SCC-induced brittle fracture behavior. These findings provide insights into the SCC behavior of ferritic stainless steel, guiding the development of more resilient, corrosion-resistant materials for various industries.

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This work aims to investigate the influence of optimized welding parameters on the corrosion performance of the lean duplex stainless steel (LDSS) UNS S32101. The correlation between microstructure and electrochemical behavior of the fusion line (FL) and fusion zone (FZ) has been investigated. In the study, six welded samples were manufactured with different welding parameters, specifically the welding current, travel speed and heat input. A mini-cell and Syringe Cell were used to characterize the electrochemical behavior of the different welded zones by means of the double loop electrochemical potentiokinetic reactivation test (DL-EPR) and potentiodynamic polarization tests. The results showed that the welding parameters tested in this study significantly affected the corrosion resistance of the LDSS UNS S32101. The heat-affected zone (HAZ) was the most susceptible zone to localized corrosion and the specific region most affected by corrosion process was that of the LDSS UNS S32101 adjacent to the FL.

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The transformation martensite-austenite and Kinetics in Ni-Ti-Hf shape memory alloys (SMAs) were calculated for the first time. The Johnson- Mehl – Avrami- Komogorov (JMAK) equation was used to simulate the transformation Martensite- Austenite, which exhibited the same trends as the DSC test results. DSC studies were conducted using four different heating rates to study the kinetics of the thermally induced transformation process and the dependence of the kinetic parameters and the heating rate. It was clarified that the heating rate adjusts the enthalpies of transformation, indicating that the heating rate can be used to adjust the phase change parameter. The Arrhenius method was used to calculate the activation energies, and it was observed from its use that the activation energies increase as there is an increase in the ternary element in the composition. Moreover, using the same heating is a valuable means of comparing activation energies for the same alloy system. This study provides a reference for designing and calculating the kinetics of Ni- Ti- Hf high-temperature shape memory alloys.

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The combination of nickel (Ni) and titanium alloy (Ti) with silicon carbide (SiC) reinforcement offers promising avenues for research and applications due to their exceptional resistance to heat, oxidation, and corrosion properties. These studies investigate the influence of silicon carbide (SiC) on Ni-Ti matrix materials, focusing on Ni-Ti-SiC composites fabricated through the microwave sintering method. The microstructure analysis reveals uniform dispersion of Ni and Ti, indicating desirable properties. This study utilized the Taguchi methodology to optimize the wear rate of Ni-Ti-SiC composites by examining sliding distance, load, and sliding velocity as essential variables. The experimental findings showed a minimum wear rate of 0.014 mg/m under certain conditions and a maximum of 0.052 mg/m under other conditions. The optimal wear rate was determined using the signal-to-noise ratio (SN ratio) at a sliding distance of 1500 m, load of 20N, and sliding velocity of 1 m/s. Sliding distance was found to be the most significant factor affecting wear rate (55%), followed by load (32%) and sliding velocity (7.3%) according to the variance analysis. Scanning electron microscope (SEM) analysis showed increased wear grooves and a smoother surface in the specimen with the lower wear rate. Atomic force microscopy was used to analyze the worn surfaces, revealing detailed 3D image patterns. Surface parameters showed significant variations between surfaces with higher and lower wear rates. Surfaces with lower wear rates exhibited minimum average roughness (6.69 nm) and maximum peak-to-valley roughness (88.65 nm).

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The reduction of cobalt oxide (Co3O4) powders was studied using hydrogen plasma (HP) and hydrogen gas at low temperatures. The reduction experiments were performed in a pulsed plasma reactor at 540 V, 532 Pa, under atmospheres of 100% hydrogen at a flow rate of 300 cm3/min, with varying times up to 60 min, and temperature range of 523–653 K. The results showed that the reduction of Co3O4 powders occurs in two steps: Co3O4 → CoO → Co, when using either HP or hydrogen gas. At lower temperatures, hydrogen plasma provided a significant increase in reduction kinetics compared to gas, since atomic hydrogen is a more powerful reductant than molecular hydrogen due to the increase in the density of crystalline defects provoked by the impact of ions incidents contained in plasma.The values for the activation energy were determined to be 35.4 kJ/mol for plasma and 90.8 kJ/mol for gas, and the kinetic equation that best fits to both experimental data was [1 – (1 – α)1/3 ]2 = k.t.

Resumo em Inglês:

Metal forming processes present many changes in the strain path necessary to obtain the dimensions and shape of a metal part. The loading mode, the amount of prestrain, the initial state of a material and its respective substructural arrangements affect the mechanical properties of different products. Many phenomena, such as the Bauschinger Effect, occur during a metal forming operation when the materials are subject to a mix of mechanical efforts. These events can be associated with changes in the dislocation substructure and crystallographic orientations. Considering the effect of strain path changes on the responses of metallic parts, this work investigates the mechanical behaviour of AISI 409 steel submitted to a loading route composed of cold rolling, tensile and shearing operations, modifying the direction of the last loading. The results indicated the effect of tensile effort and the respective dislocation substructure on the occurrence of work-hardening rate transient for the shearing carried out at 0° and a minor effect for the shearing conducted at 45° due to non-significant changes on the dislocation substructure.

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An experimental study on the distribution of residual stresses induced by shot peening on samples of SAE 1020 steel with pre-existing compressive stresses is presented. Two samples with similar geometries were subjected to a heat treatment to relieve stress. Then, one of the samples was subjected to a cementation process to introduce compressive residual stresses. Both samples, with and without cementation, were subjected to the same shot peening treatment. Using X-ray diffraction and electrolytic polishing to remove superficial layers, the depth-resolved residual stress distribution was obtained. It was concluded that the effect of pre-existing compressive stresses should be considered as a factor that influences the final distribution of the residual stresses induced by shot peening, namely the maximum of shot peening induced residual stresses moves closer to the surface in a sample with large initial compressive stresses and its value is greater than the maximum value for a specimen with lower initial compressive stresses.

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Fly ash (FA) was used successfully as a carrier for the corrosion inhibitor molybdate and applied as an extender pigment in an epoxy coating. To enhance interaction, molybdate was attached to FA through intercalation in layered double hydroxide (LDH), facilitated by surface modification of FA. Molybdate was incorporated into LDH either via direct synthesis or ion exchange. Directly synthesized LDH significantly increased molybdate storage in FA. The FA-inhibitor combination was tested in three ways: molybdate release kinetics, corrosion of an ultra-low carbono (ULC) steel in chloride solution, protection of ULC steel conferred by particles embedded in an epoxy coating. Short-term molybdate release was favored by ion exchange, long-term release by deglomeration of LDH. ULC steel corrosion inhibition in 0.1 M NaCl reached 89%. Incorporating the material into epoxy coatings mitigated steel corrosion, validated by electrochemical impedance spectroscopy. This study underscores the efficacy of FA-LDH-molybdate systems in corrosion protection.

Resumo em Inglês:

This work studied the cyclic spherical contact behavior of plasma nitrided (N) and nitrocarburized (NC) AISI 321 steel. The temperature and exposition time were 400 and 500 °C for 6 h in each treatment. A superficial hardness between ~10 (NC 400 °C) and ~17 GPa (NC 500 °C) was found by instrumented indentations; moreover, plastic and total work of indentation were analyzed. In cyclic spherical contact assessment, a critical load was first determined by applying tests between 100 and 1000 N. Next, cyclic tests were conducted with three subcritical loads (120, 150, and 180 N) and up to 105 cycles. A detrimental effect of treatment temperature was observed, 500 °C treatments presented worse failures than 400 °C, which is explained by the decomposition of expanded austenite. Between 400 °C treatments, nitrocarburizing presented a better performance, its higher plastic work of indentation is associated with a better energy absorption capacity.

Resumo em Inglês:

The main objective of this paper is to produce an anodic layer of TiO2 rich in calcium, phosphorus, and magnesium using the anodizing technique known as micro-arc oxidation (MAO) on the Ti-25Ta alloy together with the incorporation of silver (Ag), copper (Cu) and zinc (Zn) metallic ions using different electrolytes. The structural changes and microstructures on the MAO surfaces were analyzed using the X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). The chemical composition to verify whether silver, copper, and zinc were incorporated via energy dispersive spectroscopy (EDS) and surface characteristics such as wettability and hardness of the coatings were also investigated. From the EDS mapping results, it is observed that the MAO process was effective in incorporating the ions present in the electrolyte. Regarding X-ray diffraction patterns, the TiO2 phases formed in the Ti-25Ta alloy has a mixture of anatase and rutile, making the MAO surface hydrophilic. The Ag element surface is thicker than the films containing Cu and Zn, as the Ag ions have high electrical conductivity, accelerating the oxidation process during surface treatment. Regarding hardness, coating containing Cu have a higher hardness value.

Resumo em Inglês:

Structural morphology, defects, compressibility and permeability properties studied by finite element analysis, selective laser melting technology and micromorphology, mainly to analyze the effect of porosity on the performance of porous skeletal scaffolds. The results showed that during the preparation process, there are construction errors. The designed structures were able to meet the requirements of cancellous and cortical bone in terms of compressive stress and elastic modulus. The compressive stresses of the diagonal cubic compact row and octahedron are more similar at the same porosity, the elastic modulus and compressive stress decrease with increasing porosity for three structures. In the hydrodynamic analysis, the maximum flow velocity appears in octahedron up to 0.001m/s. Permeability increases with increasing porosity for all structures. The maximum permeability was obtained at 75% porosity for all structures, the pressure drop for three structures at this porosity was most similar to that of natural bone (4.153 E3 N/m3).

Resumo em Inglês:

Nickel alloys and composites are interesting engineering materials as a result of a combination of mechanical, corrosion and wear resistance at service temperatures that exceed those of steels and steel-based materials. The present study aimed at sintering Ni-graphite composites from NiO-SiC mixtures and investigate the in-situ formation of graphite. NiO powders were mixed with SiC (0, 3, 5 and 10 wt.%) and attrition-milled during 1 h. The mixtures were then granulated using 1.5 wt.% paraffin in hexane solution and uniaxially pressed under 400 MPa. The cylindrical pellets were then sintered at 1200 ºC. The sintered materials were characterized by density measurements, dilatometric and microstructural analyses, as well as Vickers microhardness. The results showed that Ni-graphite composites were successfully produced from NiO-SiC mixtures with full reduction of NiO and dissociation of SiC to form a Ni-Si matrix and graphite nodules.

Resumo em Inglês:

Since graphene and its derivatives discovery, the desire to develop accessible production methods and obtain high-quality materials to enable its production on an industrial scale has increased research interest in this field, and in techniques aiming a deep characterization of these materials. Based on this, the present study proposes a great reduction of time in the process steps of reduced graphene oxide (rGO) production. By using micronized graphite as the precursor, the exfoliation and reduction time were reduced, 67 and 75% respectively, without compromising rGO properties. Regarding the number of layers, the carbon structures presented results between 7 (rGO) and 10 (graphene oxide), being the best result of 8 layers after 10 minutes of exfoliation. Moreover, the electrical conductivity methodology proposed in this article was based on statistical analysis. The electrical conductivity of suspensions with 0.5% w/w of carbon structures was between 3400 and 3700 µS.cm-1. Thus, this study opens the way for obtaining graphene oxides by the modified Hummers’ method and shorter process time in exfoliation and reduction steps using micronized graphite as the precursor, and it also provides a methodology to determine the electrical conductivity of suspensions to assist these materials characterization without prior elimination of the solvent.

Resumo em Inglês:

This study describes titanium and zirconium incorporations into a FAU zeolite and subsequent modification with nickel hexacyanoferrate.The obtained materials (ZTiNiH and ZZrNiH) were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), X-ray Dispersive Energy Spectroscopy (EDS), Porosity and Surface Area and Cyclic Voltammetry (CV). The cyclic voltammograms of the modified ZTiNiH and ZZrNiH carbon paste electrodes in the proportions graphite-modifier (20% m/m) indicate sensitivity to isoniazid (IZN). The modified ZTiNiH carbon paste electrode displayed a linear analytical curve response from 4.0× 10–5 to 7.0× 10–4 mol L−1 and a limit of detection of 4.9×10-5 mol L-1, while the modified ZZrNiH electrode presented a linear analytical curve response from 1.0×10-5 a 3.0×10-4 mol L-1 and a limit of detection of 2.0×10-5 mol L-1. The amperometric sensitivity was 47.59 mA/mol L-1 and 20.55 mA/mol L-1 for ZTiNiH and ZZrNiH respectively. After catalytic IZN electro-oxidation, a study concerning the main IZN interferents was performed and its recovery from a synthetic urine sample was assessed. The obtained ZTiNiH and ZZrNiH materials are noteworthy for their good limit of detection and recovery eficiency when applied to real samples, thus comprising potential candidates for the development of electrochemical sensors aiming at IZN detection.

Resumo em Inglês:

In the present study, non-thermal plasma (NTP) of dielectric barrier discharge (DBD) was used to investigate the precipitation of salt from hypersaline waters obtained by evaporating seawater. A dripper was used to release drops of water over the NTP discharge between the droplet surface and a copper ring in a glass tub working as a DBD. Results showed that the precipitation rate of the NTP-treated solution was significantly higher than that of the untreated solution, with a larger number of small crystals formed, and multiple charged ions preferentially precipitated. These findings suggest that the external electric field from NTP aligns and weakens the hydration of ions, leading to the binding of dehydrated cations and anions, and inducing nucleation/precipitation. Additionally, the NTP discharge channels formed at the gas-liquid interface cause rapid dehydration of ions, which further induce nucleation and crystal formation. This could explain the preferential precipitation of small crystals containing multiple charged ions. Overall, the results demonstrate that NTP-DBD is a promising approach for efficient precipitation of salts from hypersaline waters.

Resumo em Inglês:

In this work, epoxy resin-based composites reinforced with nanoclays, nanoalumina, carbon nanotubes (CNTs) (0.15, 0.50, and 1.50% vol were submitted to morphological characterization by scanning (SEM) and transmission (TEM) electron microscopies, electrical tests through electrical impedance spectroscopy, and electromagnetic analyses (scattering parameters), in the frequency range of 8.2 to 12.4 GHz. SEM images of the CNT composite revealed nanotube clusters in the matrix. The proximity between the CNTs is corroborated by the increase in the electrical conductivity of the composite due to the formation of a long-range electron transport network, which favored the polarization effect, absorption losses (SEA = 1.33 dB), reflection (SER = 3.38 dB) and reflection loss (RL = -6.61 dB at 10.8 GHz). Composites with nanoclays and nanoalumina showed no significant electrical and electromagnetic results.

Resumo em Inglês:

Ti/Al/Ti laminated composite material is an ideal material for high-temperature parts and protective armor in the aerospace field because of its high specific strength and high temperature oxidation resistance. To improve the joint strength, the ultrasonic welding solid-phase joining technology is used to prepare Ti/Al/Ti laminated composites. The results show that the temperature, microstructure and microhardness distribution of the aluminum interlayer are uniform after welding. The recovery recrystallization behavior reduces the hardness of the aluminum interlayer during welding, while the microstructure and microhardness of the upper and lower titanium layers do not change significantly. The tensile shear failure positions of the joints are all located in the lower Al/Ti interface layer, and the highest tensile shear strength reaches 124.4 MPa (1200 W). At this parameter, the plastic constraint reinforcement effect is the most significant, the interface exhibits a small amount of vortex-like morphology, and the local area of the aluminum material melts below the equilibrium melting point. When the welding power reaches 1400 W, the upper surface of the weld is crushed, and the TiAl2 IMC phase precipitates in the Ti/Al interface region.

Resumo em Inglês:

Polyethylene of Raised Temperature Resistance (PE-RT) is a specially designed high-density polyethylene utilizing bimodal resin technology. It is suitable for oil and gas pipeline applications, exhibiting excellent long-term creep resistance at elevated temperatures. Flexible risers require security against potential offshore oil leaks, prompting the reinforcement of PE-RT with graphene oxide (GO) at concentrations of 0.5, 1.0, and 2.0 wt.%. The nanocomposites were processed in a twin-screw mini extruder at 180°C, with a screw speed of 100 rpm and a residence time of 6 min. The results indicated an increase in the thermal stability of the nanocomposite by 14°C. XRD and DSC analyses revealed a higher crystallinity index for the sample with the lowest GO content. The water contact angle values increased from 98° in the pure matrix to 102° in the nanocomposite, suggesting a slight increase in the material's hydrophobicity due to nanoparticle incorporation. SEM images demonstrated a good interface between GO nanoparticles and PE-RT without agglomeration. The Shore D hardness increased from 50 to 59 with 2.0 wt.% GO. Although the 0.5 wt.% GO composition exhibited a higher degree of crystallinity, other properties such as thermal resistance, Shore D hardness, contact angle, dispersion, and homogeneity tended to improve with increasing nanoparticle content. Consequently, it can be concluded that the optimal concentration of GO in the PE-RT matrix is approximately 1.0 wt.%. Incorporating 1.0 wt.% GO resulted in an increase in Young's modulus from 335 ± 37 MPa to 409 ± 42 MPa, indicating enhanced mechanical strength of PE-RT. Finally, aging tests showed that GO reduced the swelling degree of the final material, suggesting that PE-RT/GO is a promising candidate for pipeline applications.

Resumo em Inglês:

This work addresses the corrosion resistance of Riser steels used in submarine pipelines for oil production, making it crucial to evaluate the variables related to corrosion in the marine environment. Three types of wires with spheroidized, lamellar and discontinuous cementite microstructure were tested in 0.1M H2SO4 with and without the use of CO2, in addition to a different ambient temperature (80 °C). Thus, electrochemical tests, including OCP and linear potentiodynamic polarization, revealed the corrosion resistance of each material. The analysis of the polarization curves through Tafel extrapolation, obtained the current density, correlating with the potential of the sample in the medium, indicating the polarization resistance. The LC wires demonstrated greater resistance to corrosion (769.23; 2,544.79 and 4,790.87 Ω.cm2) compared to spheroidized cementite (502,40; 1,038.99 and 902.95 Ω.cm2) and, which, in turn, obtained lower resistance values in two of the solutions. The FeCO3 and FeSO4 salts were formed in different areas, including the most degraded ones identified by Raman spectroscopy.

Resumo em Inglês:

In this work, the asymmetrical rolling of 860 μm thick high-purity titanium (HP-Ti) strips is investigated. HP-Ti ultra-thin strips are produced in thicknesses ranging from 280 μm to 20 μm. The microstructure and texture evolution of HP-Ti ultra-thin strips were analyzed using electron backscattering diffraction (EBSD), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The raw strips have a homogeneous and equiaxed microstructure, containing some face-centered cubic (FCC) Ti laths. With a rise in rolling reduction, equiaxed grains change into deformation structures characterized by a high density of dislocations. The formation of an ultra-fine grained microstructure and the elimination of FCC-Ti laths come next. The influence of grain rotation and slip systems on the development of texture in ultra-thin strips during rolling reduction is illustrated through the analysis of {0002} pole figures and orientation distribution function. The tensile qualities of ultra-thin strips are correlated with their microstructure.

Resumo em Inglês:

This study aims at showing the influence of transformation-induced plasticity (TRIP) on the residual stresses and magnetic permeability of AISI 304 stainless steels and the resulting effect on its fatigue performance. Samples were pre-strained to different levels of plastic deformation, and characterised through metallography, hardness, tensile testing, X-ray diffraction (XRD) and with the MWM®-array electromagnetic method. Fatigue tests were then conducted on these samples to obtain the S-N curves for each condition, and the resulting fracture surfaces were analysed using scanning electron microscopy (SEM). Residual stress distributions in martensite and austenite were significantly affected by the transformation, although in different ways, and this is thought to be the reason for the improvement in fatigue performance in samples with higher pre-deformation values. Magnetic permeability measurements corroborated XRD results and proved to be a useful tool for non-destructively determining martensite transformation distributions in manufactured components.

Resumo em Inglês:

Aluminum Hybrid Metal Matrix Composites (Al-HMMCs) are contemporary materials that blend aluminum with additional reinforcing elements to enhance their mechanical, thermal, and other properties. These materials find applications across various sectors including the aerospace industry, automotive sector, military and defence, marine industry, as well as manufacturing industries. In this research, AA6061, zirconium dioxide (ZrO2) and boron carbide (B4C) have been selected as the matrix and reinforcement materials. AA6061/ZrO2/B4C (Al-HMMCs) is manufactured using Ultrasonic-assisted stir casting. The process parameters of ultrasonic assisted stir casting were optimized with the help of Taguchi optimization technique. The melting temperature (700, 750 and 800 ºC), stirring speed (10, 15 and 20 minutes) and AA6061/xwt.%B4C/xwt.%ZrO2 ( 6, 8 and 10) are selected as input parameters for optimization. The reinforcements ZrO2 and B4C are weighed by equally sharing by wt.% The micro hardness was selected as response parameter and it was determined by using Vickers micro hardness tester. The L9 Orthogonal Array (OA) was employed for optimization of input parameters of ultrasonic assisted stir casting. Taguchi results showed that medium level of melting temperature (750 ºC), higher level of stirring speed (300 rpm), lower level of stirring duration (10 minutes) and medium level of wt.% of ZrO2 and B4C (8wt.%) were the optimized combination of input process parameters of ultrasonic assisted stir casting for fabricating AA6061 HMMC. The AA6061/xwt.%B4C/xwt.%ZrO2 (x = 0,4,6,8 and 10) HMMCs were manufactured by utilizing optimized process parameters. The micro hardness of AA6061/xwt.%B4C/xwt.%ZrO2 (x = 0,4,6,8 and 10) was determined. . From the obtained hardness tests, it was observed that the hardness of AA6061 HMMCs was enhanced up to addition of 8wt. % of B4C and ZrO2 and decreased the hardness while adding 10wt.% of B4C and ZrO2. The better AA6061/8wt.%ZrO2/8wt.%B4C HMMC undergone X-ray Diffraction Analysis (XRD) and Scanning Electron Microscope (SEM) testing to identify elements and examine the microstructure. The high peak of ZrO2, B4C and Al was obtained in 71.4, 35.68 and 37.81 2 theta values respectively. The SEM image of ultrasonic aided stir cast AA6061 based composite was confirmed the uniform distribution of zirconium di oxide and boron carbide reinforcements. There was no oxide formation on the surface of the stir casted AA6061 composites due to the execution of casting process in the inert environment. The casted AA6061/8wt.%ZrO2/8wt.%B4C surface of the composite exhibits no porosity occurrence due to the impact of usage of ultrasonic vibrator to prevent the formation of holes due to escape of unwanted gases. Subsequently, corrosion tests were conducted on the AA6061 HMMC in various corrosive environments such as NaOH, HCl, H2SO4, and NaCl to evaluate its electrochemical behavior. The surfaces of corroded specimens were analyzed using SEM and Energy Dispersive Spectroscopy (EDS). The research findings indicate that AA6061 composites exhibit the highest corrosion resistance when immersed in a NaCl medium. This enhanced resistance was attributed to the medium's lower corrosion potential, stronger charge transfer resistance (Rct), and lower double-layer capacitance (Cdl) compared to alternative environments. Additionally, SEM analysis illustrated that the incorporation of B4C and ZrO2 ceramics results in the formation of protective barrier layers, further enhanced their corrosion resistance. ZrO2 particles were attracted and neutralized the corrosive ions and electrons, thereby reducing corrosive activity on the AA6061 aluminium matrix.

Resumo em Inglês:

PEO/TiP fibers were obtained using the Solution Blow Spinning (SBS) apparatus and heat treated to produce TiO2 fibers. The morphological and structural characteristics were assessed using SEM and X-ray diffraction. The fibers, with a thickness of 12 μm, showed a change in crystalline structure with heat treatment. At temperatures as low as 800 °C, only the anatase phase was identified, while at 900 °C, both anatase and rutile phases coexisted. The addition of TiP to the polymer matrix reduced the initial breakdown temperature, and the DSC curves showed exothermic peaks due to the amorphous phase transition to TiO2/anatase. The fibers' photocatalytic capacity was tested, revealing that TiO2-fibers in the anatase phase achieved 97% degradation of Rhodamine-B dye in 40 minutes. The study found that the biocide efficacy of TiO2-fibers depends on their heat treatment. Fibers with anatase/rutile or pure rutile phases did not show significant efficiency. However, fibers treated at 600°C with pure anatase phase were more effective in eliminating E. coli and total coliforms. Finally, we can state that the TiO2 fibers obtained in this work using the SBS technique can be used to produce filters to purify water contaminated by pathogens dangerous to human health or even to purify the air.

Resumo em Inglês:

In plasma nitriding of cutting tools, edge embrittlement can result from both, deepest layer, and grain boundaries precipitation. Overheating and surface charge density concentration in Direct Current Plasma Nitrided (DCPN) can be reduced through an indirect source of plasma, called Active Screen Plasma Nitriding (ASPN). The removal of the oxide layer from previous processes, such as heat treatment, is required in DCPN samples. This metallographic preparation can be a challenge in more delicate locations, such as on edges. This preliminary step is not usually described in studies comparing DCPN with ASPN. In the present work, a special pre-nitriding procedure aims for edge integrity and equivalent surface state at the top and the flank of AISI M2 samples. Under standard temperature (500°C) and atmosphere (2.5mbar, N2/H2:25/75), ASPN and DCPN were conducted for 2 and 4 hours, respectively. Edge cross-sections were analyzed in an Olympus GX-51 optical microscope (OM) and in a Carl Zeiss EVO MA 15 Scanning Electron Microscope (SEM). ASPN was effective in reducing embrittlement caused by grain boundary precipitation at a plasma nitrided edge.

Resumo em Inglês:

The present study features analytical and experimental results of AA5754/DP600 dissimilar joints produced by the refill friction stir spot welding of 1.5-mm-thick sheets. The selection of proper parameters for this process, such as tool rotational speed (RS), welding time (WT), tool plunge depth (PD), welding force (WF) and backing plate material played an important role in assuring weld strength. In this work, experimental tests were carried out based on the welding conditions according to Taguchi method, in order to determine optimal welding parameters and investigate the effect of those in the joint’s mechanical properties. Analysis of variance (ANOVA) was also applied to determine the individual importance of each parameter on the lap shear strength (LSS). The results showed that the use of a backing plate with high conductivity during the welding process is a critical factor for control the formation of intermetallic layer on the interface of the joints and consequently increase the mechanical properties of the joints. Additionally, the results based on lap shear strength indicated that tool rotational speed was the parameter with the largest influence on the joint shear resistance. In contrast, DT was shown to have no significant influence on the joints performance for the selected range tested.

Resumo em Inglês:

This study investigates the incorporation of hafnium (Hf) into polyurethane foams (PUs), an underexplored area in polymer materials research. The synthesis of Hf-containing PU foams was conducted, and their characterization was performed using Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), optical microscopy (OM), and dynamic mechanical analysis (DMA). The results revealed a significant increase in the stiffness of PU foams due to the potential formation of hafnium isocyanate. Quantitative values obtained through DMA tests demonstrated an approximate increase of 95.97% for PU Hf 0.5% and 342.72% for PU Hf 3%, compared to the sample without Hf. These data highlight the influence of hafnium on enhancing the mechanical properties of polyurethane foams.

Resumo em Inglês:

The corrosion resistance of an epoxy resin-based coat, reinforced with 0.1 and 0.5 wt% of reduced graphene oxide (rGO), applied to AISI 1020 carbon steel was subjected to immersion tests on a 3.0 wt% NaCl solution saturated with CO2 in a pressurized cell with 70 bar at 40 °C for 528 hours. The coating was accessed via pull-off testing, and scanning electron microscopy (SEM) was used to analyze porosity and thickness. Optical Microscopy (OM) assessed the condition of the metallic surface. Adding rGO generated greater corrosion protection and improved the structural integrity of the coating for the conditions studied. With 0.1 wt% rGO, there was a pore refinement, and with 0.5 wt%, pore density was drastically reduced. The addition of rGO did not influence the coating Shore D hardness coating. Post-corrosion test results indicated that porosity and solution permeation were related, and the anchorage of the coating to the substrate was not affected.

Resumo em Inglês:

Super duplex stainless steels are highly recommended for corrosive environments. However, detrimental phases tend to precipitate in the austenite-ferrite interfaces at certain temperatures. In this study, the elastic moduli of ten specimens of SAF 2507 that underwent isothermal heat treatment at 900 ºC for different amounts of time were determined using the ultrasonic non-destructive technique. These results were validated by nanoindentation, confirming the accuracy of the ultrasonic inspection. An investigation of microstructural changes, employing optical microscopy and X-ray diffraction, enabled elucidation of how these modifications influence acoustic wave attenuation and velocity, as well as the elastic modulus. As the ferrite content decreases and the sigma phase content increases, the attenuation coefficients tend to decay, while the elastic modulus increases until a treatment time of 45 min and remains stable for higher aging times. Additionally, a robust correlation between shear wave velocity and the elastic modulus was identified.

Resumo em Inglês:

The aim of this study was to assess the impact of rail metallurgy, focusing on segregations and chemical composition, and welding parameterization on the quality and susceptibility of welds to defects and failures induced by mobile flash butt welding (FBW). Ten welds were performed using two different welding programs, with varying heat input, on premium rails sourced from the same batch. The welds underwent full metallurgical characterization of the weld and HAZ, including hardness profile, mechanical testing, and micrographic analysis of the head, web, and foot regions. The results showed that both the HAZ dimensions and the hardness profile are influenced by weld parameterization. All welds fabricated by the lower heat input program, small islands of martensite and retained austenite (MA) were observed only in the foot region, close to the weld line. From the higher heat input program, only one weld showed islands of MA. Localized chemical analysis indicated that the formation of these islands is linked to microsegregation, especially of Mn and Cr present in the rail.

Resumo em Inglês:

In this study, cellular spacing, porosity and corrosion of 1050 aluminum alloy subjected to the different levels of Gamma radiation was examined using a Gammacell Co-60 type irradiator, with activity of 16.13 TBq and dose rate around 6.98 Gy/min. Samples were extracted from an aluminum ingot, which was obtained with directional solidification apparatus. This upward directional solidification technique allowed obtaining of aluminum samples under different conditions of cooling rates. Firstly, cooling rates were determined during solidification experiment and then correlated to the cellular spacings and porosity content. The experimental results pointed out that cooling rates exerts a strong effect on the microstructural patterns and porosity formation. Laws have been determined, indicating that increase in cooling rates favored a refinement effect on as-cast microstructure and a decrease in porosity content. Furthermore, measurable effects of different levels of the Gamma radiation on the microstructure, porosity and corrosion for samples of 1050 aluminum alloy, were determined. The experimental results show that Gamma radiation has favored changes in cellular spacings, porosity formation and corrosion behavior. From this results, one can conclude that coarser microstructures, porosity formation and corrosion are favored by prolonged thermal annealing caused by temperature field generated during Gamma radiation exposure. On the other hand, even after the exposure to different levels of Gamma radiation, the microstructure and porosity observed in as-cast samples are still strongly dependent of the cooling conditions.

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TC4 (Ti6Al4V) alloy is widely used in aerospace, medical equipment, food industry and other fields. Laser powder bed fusion (LPBF) technology has a short production cycle and high precision for formed parts, providing new ideas for the manufacturing of complex structures such as aerospace and having great development prospects and manufacturing advantages. This paper took the TC4 heat dissipation structure prepared by LPBF technology as the study object and established a numerical simulation model to analyze the temperature field changes of the TC4 heat dissipation structure prepared by LPBF. By adopting the annealing heat treatment process, it was found that with the increase in annealing temperature and holding time, the microstructure coarsened, the hardness first increased and then decreased, and the corrosion resistance improved. Among them, when the annealing temperature was 900 °C, and the α' phase was basically transformed into α phase, and the content of β phase increased. The grains and structure of the heat dissipation structure were uniform, and the most significant was in the near inner-pore area. At this point, the hardness value significantly decreased, and the difference in hardness around and outside the heat dissipation hole was 12.42 HV0.2.

Resumo em Inglês:

The work evaluated the nucleating effect of nanometric zirconia (Zr-NP), obtained by the green sol-gel synthesis route using Euclea natalensis root extract as a reductant, in the low-density polyethylene (LDPE). The Zr-NP was characterized with x-ray diffraction (XRD) and transmission electron microscopy (TEM) which confirmed the presence of Zr-NP in the cubic crystalline phase with an average particle size of 6.73 nm. The Zr-NP was incorporated into the polymeric matrix by solubilization in concentrations ranging between 0 wt% and 6 wt%. Non-isothermal DSC analyzes demonstrated that a small addition of 1 wt% changes the degree of crystallinity from ~23% to ~56%, an increase of ~137%. The addition of Zr-NP also caused a small increase in crystallization and melting temperatures, and a large increase in the total crystallization time of LDPE.

Resumo em Inglês:

Alum sludge (AS) from water treatment plants is an abundant, non-toxic residue with high Si and Al contents. These characteristics make it an ideal precursor for zeolite synthesis, not only reducing the environmental impacts from AS disposal but also adding value to the waste by promoting its reuse. Herein, we propose a route to prepare zeolitic materials from AS, aiming for its application as a component of slow-release fertilizers, using mild conditions and cost-effective hydrothermal synthesis. X-Ray Diffraction revealed the formation of sodalite (Na-SOD) in short times (5-10 h) and moderate temperatures (100-120ºC), with sodium silicate addition favoring Si-quartz consumption and zeolite crystallization, without a fusion step. The Na-SOD showed a desirable cation exchange capacity, reaching 117 mg g-1 for K+. A K-SOD fertilizer was then prepared with an average 490 nm size, 2 m2 g-1 BET surface area, and slow-release behavior. Incubation in soil confirmed that Al was inactive in K-SOD and did not immobilize phosphate, in addition to promoting high K+ availability. The results support the potential of AS reuse for application in agriculture as an efficient and sustainable fertilizer.

Resumo em Inglês:

This study presents the synthesis and in-depth evaluation of a novel Tin(IV) oxide/reduced graphene oxide (SnO2/rGO) nanocomposite developed as an electrode material for advanced electrochemical supercapacitors. Utilizing a scalable synthesis method with optimized parameters, the resulting nanocomposite was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), revealing its well-defined morphology, crystal structure, and composition. Comprehensive electrochemical assessments, including galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV), demonstrated that SnO2/rGO exhibits superior performance metrics compared to pure SnO2. Notably, at a current density of 1 A g−1, the SnO2/rGO nanocomposite achieved a specific capacitance of 140 F g−1, surpassing the 133 F g−1 of pure SnO2. These findings highlight the SnO2/rGO nanocomposite's potential to significantly enhance energy storage capabilities, making it a promising candidate for applications in electric vehicles, portable electronics, and sustainable energy systems.

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Cryogenic treatment enhances the properties of cutting tools. This study investigates the effects of shallow and deep cryogenic treatments to TiAlSiN coated tungsten carbide tool used in end milling of maraging steel C300. Experiments are conducted in a three axis CNC vertical milling machine at various spindle speeds using TiAlSiN coated tool without cryogenic treatment (UCT), shallow (SCT) and deep (DCT) cryogenically treated coated tools. The surface finish obtained during milling of slots, built-up edge of tools and the tool wear are investigated and compared. With an increase in spindle speed, SCT tool showed an improvement of 13.3% with UCT and 33.5% with DCT. Formation of built-up edge on the cutting tools are also evaluated and compared. Tool wear is quantified, in which SCT tool showed lowest tool wear in comparison with UCT and DCT tools.

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Residual stresses exist intrinsically in any manufactured or processed material, significantly influencing its mechanical properties. Shot peening enhances fatigue life by introducing compressive residual stresses at the surface, however, the beneficial effects may be reduced under external loads. This study investigates the behavior of surface residual stresses induced by shot peening in API 5L X80 steel. Specimens underwent tensile monotonic loading cycles below the yield strength, incrementally increasing the load until reaching the yield limit. Residual stresses were measured using the X-ray diffraction by sin2ψ method, revealing a progressive stress relief of compressive residual stresses field induced by shot peening. The development of tensile residual stresses was observed following the monotonic tests. Loads below yield stress were able to completely reverse compressive stresses to tensile stresses. A correlation was observed between residual stresses and magnetic Barkhausen noise, suggesting it as a potential method for analyzing residual stress behavior qualitatively in shoot peened steel samples.

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Piezoelectric ultrasonic sensors used in Structural Health Monitoring (SHM) systems are usually attached to components by using adhesives with intrinsic properties that end up affecting their frequency-response. In this work, the electromechanical impedance of sensors attached to an aluminum sheet with three different epoxy resins was monitored during curing. Impedance change indexes (CIs) were calculated and compared with cure degree estimations from Differential Scanning Calorimetry (DSC). Results show that resonance frequencies were displaced by up to 30 kHz, and amplitudes changed considerably during the curing process of the selected resins. Results indicate that certain CIs show a high positive correlation value (R=0.96) with DSC data, and could therefore be used in practical applications to evaluate the curing status of the adhesive in SHM applications.

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A versatile nature of polyurethanes allows for the modification of thermal, mechanical, and chemical properties, making them promising candidates for medical applications. This study focuses on the synthesis, characterization, and biocompatibility evaluation of a novel poly (L-co-D,L-co-lactic acid-co-Caprolactone)urethane (PLDLA-PCL-PU) material derived from L-lactide, D,L-lactide, polycaprolactone-diol (PCL-diol) and 1,6-hexamethylene diisocyanate (HDI). This research performs a meticulous two-stage synthesis process, ultimately leading to the formation of PLDLA-PCL-PU through polymerization of the prepolymer (PP) and HDI. The confirmation of successful synthesis and the characterization of PLDLA-PCL-PU was done by FTIR-ATR, and 1H NMR. As evidenced by XRD, the amorphous nature of PLDLA reduces the degree of crystallinity in PLDLA-PCL-PU. Thermal decompositions, as well as the associated thermal events, were investigated using TGA and DSC. The biocompatibility of the material was evaluated using human mesenchymal stem cells. These assays reveal a notable enhancement in cell metabolic activity and proliferation when in contact with polyurethane membranes. By combining the properties of polyurethanes with the custom design of PLDLA-PCL-PU, this research strives to contribute with the advancement of biomaterials that promote tissue regeneration.

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The properties of a hot-deformed component can be enhanced by planning its forming process within the desired thermal processing-parameter windows associated with dynamic recrystallization (DRX). In order to determine the windows of 40Cr10Si2Mo steel, hot compression tests were employed within the deformation conditions of 1173-1398 K and 0.01-10 s-1. Following this, the hot processing maps, which distinguished the parameter domains with stable plastic deformation, were established according to the stress-strain data. The DRX domains were further identified within the stable deformation domains and represented as a map illustrating the deformation mechanisms of this steel. The deformation activation energy, which describes the forming difficulty degree of material, was calculated, and its evolution map with parameters was constructed. The deformed microstructures were characterized utilizing a scanning electron microscope (SEM) to verify the deformation mechanism map. An enhanced processing map which superimposed the activation energy map over the deformation mechanism map, was developed. The resulting map facilitated the determination of optimal windows that ensure DRX mechanism and lower activation energy. The optimal windows for 40Cr10Si2Mo steel were finally obtained as: 1322-1398 K & 0.016-0.35 s-1 and 1344-1380 K & 0.035-0.126 s-1.

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Modifying the surface of titanium alloys with a laser considerably increases the specific area, which has beneficial implications for the osseointegration process. In this study, Yb:YAG laser was used to modify the surface of the commercial β-type Ti-15Mo alloy. The process parameters used were based on a suitable osseointegration condition for this treatment. The effect of such modification on the fatigue performance of the alloy was analyzed. To assess the impact of surface modification on the alloy’s fatigue performance, axial fatigue tests were conducted on specimens with both polished and laser-modified surfaces (R = 0.1). Fatigue strength was evaluated using a staircase method, where specimens were subjected to varying maximum stress levels to determine the fatigue limit after 5x106 cycles. The results showed that the laser-modified surface presented cavities and roughness values such that the effect on fatigue was highly detrimental. A reduction of around 75% in the fatigue limit (maximum stress) was obtained, indicating that modifying the Ti-15Mo alloy with laser for medical purposes may require integrated biological-mechanical development.

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Enhanced corrosion-resistant Ni-Cu-P amorphous coatings were applied to AZ91D magnesium alloy substrates using an integrated approach that included direct-current (DC) copper pre-plating and electroless Ni-Cu-P plating at varying CuSO4 concentrations. The effects of CuSO4 concentration on the microstructure, electrochemistry behavior and corrosion rate of Ni-Cu-P coatings and the adhesion between the Ni-Cu-P coating and the magnesium alloys substrate were investigated. The results indicated that the surface of the Ni-Cu-P ternary coating which integrated well with the magnesium alloys substrate exhibited heterogeneous cell structure with relatively flat and dense structure. When the CuSO4 concentration was 0.8 g/L, the mass fraction of P in the coating was 9.06 wt% meaning amorphous Ni-Cu-P coating. The results of the Nyquist and Bode graph, corrosion rate, corrosion morphologies and of the Ni-Cu-P coatings with different CuSO4 addition indicated that the corrosion resistance reached optimization with corrosion potential of -0.31 V, the corrosion current density of 0.0039 A/cm2 when the CuSO4 concentration is 0.8 g/L. Furthermore, the adhesion test confirmed that the adhesion of Ni-Cu-P coatings improved gradually as the CuSO4 concentration increased and exhibited optimum when added 1.0 g/L CuSO4. The obtained Ni-Cu-P coating with amorphous structure prevented effectively magnesium alloy from corrosion.

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Herein stacked layers of Nb2O5 coated onto Al substrates are fabricated as microwave resonators. Structural and morphological analyses on these stacked layers have shown the amorphous nature of growth of the stacked layers. Electrically, the resonators showed negative capacitance effect accompanied with series and parallel resonance at three well -distinguished notch frequencies. Additionally, the resonators exhibited bandstop filter characteristics with notch frequency (fn) centered at 1.05 GHz, return loss (RL) value of 9.0 dB and voltage standing wave ratios (VSWR) of 2.12. To enhance the performance of the Nb2O5 microwave resonators, platinum nanosheets of thicknesses of 50 nm were inserted between layers of Nb2O5. Platinum nanosheets successfully decreased the surface roughness and increase the electrical conductivity by five orders of magnitude. Pt nanosheets additionally improved the values of fn, S11, RL and VSWR to 1.16 GHz, 0.039, 30.3 dB and 1.12, respectively. The features of the microwave resonators comprising Pt nanosheets in its structure are promising for using them in communication technology.

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The influence of polyacrylamide and multi-wall carbon nanotubes as binders for the granulation process for iron ore sintering was investigated in conditions of high proportions of ultrafine (< 0.150 mm). The binders were added to the sintering mixtures composed of 20 and 40 wt.% pellet feed and then subjected to granulation tests in an HPS laboratory scale route. The granules obtained were analyzed by particle size, shatter test (degradation), and cold permeability after granulation, degradation, and drying. A decrease in the granules’ size with the addition of polyacrylamide was observed due to decreased granulation efficiency, leading to low cold permeability of the granules. Adding nanotubes dispersed in burnt lime resulted in the improvement of the granulation process, presenting larger, more resistant and more permeable (before/after degradation) granules. After drying, the bed permeability of granules produced using polyacrylamide or nanotubes decreased significantly, pointing to low performance in the sintering dry zone.

Resumo em Inglês:

Calcium hexaluminate (CA6) presents a wide application in high-temperature thermal insulation. Despite the high porosity levels achieved, the use of carbonated precursors in its synthesis inevitably produces CO2 as a by-product. CA6 was produced by combining different sources of alumina (α-Al2O3 and ρ-Al2O3) and lime (CaCO3, Ca(OH)2, and CaO) in aqueous suspensions that were cast and sintered to evaluate these routes on its physical properties. The products attained after sintering at 1550 and 1600 °C were characterized for crystal phases, real density, particle morphology, uniaxial compressive strength, apparent porosity, and pore size distribution. Part of the samples sintered at 1600 °C was subjected to a thermal shock test and was then evaluated for residual strength under diametrical compression, apparent porosity, pore size distribution, and flexural elastic modulus. The CA6 samples produced from α-Al2O3 presented lower pore fraction and higher mechanical strength and modulus of elasticity. The superior properties of the materials produced with α-alumina were maintained after thermal shock. The acicular geometry of the CA6 particles is related to their excellent thermal shock resistance and mechanical performance. The results indicated a more environmentally friendly system produced from α-Al2O3-CaO for industrial applications of high-temperature thermal insulation resistant to thermal shock damage.

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Aluminium Metal Matrix Composites (AMMCs) reinforced with a particulate form of reinforcement have emerged as a replacement for monolithic alloys in various engineering industries due to their superior mechanical properties and customizable thermal and electrical characteristics. Silicon Carbide (SiC), is renowned for its high-temperature strength, hardness, wear resistance, excellent oxidation resistance, chemical resistance, low thermal expansion, high thermal conductivity, and compatibility with aluminium alloy find extensive utilization in Shipbuilding industries. The necessity for joining AMMCs arises in numerous engineering applications. Friction Stir Welding (FSW) emerges as one of the most fitting welding processes for joining AMMCs reinforced with particulate forms of ceramics without compromising their superior mechanical properties. This study endeavours to establish regression models predicting the Ultimate Tensile Strength (UTS), Percent Elongation (PE), and Weld Nugget Hardness (WNH) of friction stir welded AA6092 matrix composite reinforced with Silicon Carbide particles (SiC). The models correlate significant parameters such as tool rotational speed (TRS), welding speed (WS), axial force (AF), and percentage of SiC reinforcement in the AA6092 metal matrix. Statistical software Design Expert, along with analysis of variance (ANOVA) and student’s t-test, is employed to validate the developed models. It is observed from the investigation that these factors independently influence the UTS, PE, and WNH of the friction stir welded composite joints. The developed regression models are optimized to maximize the UTS and WNH of friction stir welded AA6092/SiC composite joints.

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In this study, the surface of ZL104 was ultrasonically rolled (USRP) to provide better overall mechanical properties and corrosion resistance. USRP experiments were conducted on the surface by setting different parameters to improve the performance of ZL104 after strengthening. The results of the gradient residual stress test showed that the specimen with parameter 350N, 4-pass had 95.5% increase in residual stress and better fatigue resistance. The corrosion resistance of the specimen with a parameter of 500N, 3-pass was superior to that of the original specimen, with an increase of about 50%. The surface roughness test results showed that the surface roughness was reduced by about 38%-50% after USRP treatment. Meanwhile, the microstructure (OM, SEM) results showed that the surface grains were refined and the hardness increased from 105.45HV to 197.61 HV after USRP processing, and the properties were optimized.

Resumo em Inglês:

Efficient thin film solar cell technologies, including Cu(In,Ga)(S,Se)2 (CIGS) and CdTe-based cells, have advanced significantly. Yet, environmental concerns and element scarcity fuel the pursuit of alternatives. Copper zinc tin sulfide (Cu(Zn,Sn)(S,Se)2 or CZTS) garners attention for its use of non-toxic, abundant elements. We present a study on CZTS thin film solar cells via low-temperature chemical synthesis. The process involves dissolving Copper (II) acetate, zinc (II) acetate, and tin (II) chloride in 2-methoxyethanol and monoethanolamine to create a metal compound solution. This solution is spin-coated onto molybdenum-coated glass substrates and annealed at 300 °C. The CZTS layer is sulfurized at 400 °C using di-tert-butyl-disulfide (TBDS). Characterization utilized diverse techniques. Scanning electron microscopy (SEM) revealed smoother surfaces post-sulfurization. Optimized compositions, Cu-poor and Zn-rich, vital for enhanced efficiency, were confirmed through energy-dispersive X-ray spectroscopy (EDX). X-ray diffraction (XRD) patterns aligned well with the kesterite phase, with additional phases like ZnS, SnS, SnS2, and CuS detected. X-ray photoelectron spectroscopy (XPS) offered insights into composition and surface contamination. High-resolution scans provided binding energies, validating the film's composition. This study enhances the comprehension and realization of CZTS thin film solar cells, offering a potential avenue for earth-abundant, efficient photovoltaics.

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This paper investigates the effect of Fe contamination on the microstructure and mechanical properties of Al-7Si-0.7Mg-Fe2.5 alloy processed by Laser Powder Bed Fusion (LPBF) and heat treated in two different conditions: (1) Solution Heat Treatment (SHT) at 520 °C, followed by artificial ageing at 160 °C (T6), and (2) Direct Artificial Ageing of the as-printed material at 160 °C (DAA). Microstructural characterization was carried out by Optical Microscopy (OM), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscope (TEM). Mechanical characterization was carried out by tensile tests at room temperature. The formation of fine AlSiFe phases such as α-AlFeSi and β-AlFeSi had no deleterious effect on the mechanical properties compared to previous studies for AlSiMg alloys without Fe. However, compared to the as-printed condition, the T6 heat treated sample decreased the ultimate tensile strain significantly, while the elongation to the fracture presented a slight improvement.

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Borate bioactive glasses are more soluble than silicate’s and convert rapidly and completely into hydroxyapatite (Ca5(PO4)3(OH)), being more suitable for wound healing applications than their silicate counterparts. In this work, the 45B5 composition (46.1 B2O3 – 26.9 CaO – 24.4 NaO – 2.6 P2O5, mol%)) were embedded into electrospun PHBV (Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)) nanofibers by encapsulation and/or electrospray deposition aiming to produce a wound dressing with optimized bioactivity and antibacterial properties for wound healing applications. The fibers were characterized regarding their physical, structural, and thermal properties, and in vitro by L929 Mouse Fibroblast Cell Line adhesion, migration, and cytotoxicity and by its antibacterial activity against the bacteria S. aureus. The set of characterizations evidences that the encapsulation method was the most promising for the 45B5 embedding into PHBV nanofibers, as it produced a wound dressing with great loading efficiency (70%) with a highly hydrophilic surface, leading to expressive adhesion, migration, and viability of L929 cells and antibacterial activity. Thus, the nanofibers produced by the encapsulation method alone provided a dressing with high potential in wound healing management.

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In this study, two solid-state preparations were proposed for ultra high molecular weight polyethylene (UHMWPE) modified by the polyethylene glycol (PEG). Some samples were grinding in a high-energy mill and the other in a ceramic jar mill (CJM). The objective of this work is to investigate the lubricating effect of PEG on UHMWPE through mechanical milling to evaluate the homogenization and properties of the resulting material. The mixtures in the CJM presented a more uniform morphology. These compositions showed increases in crystallinity greater than 22%, attributed to the molecular mobility caused by the lubricating effect of PEG. Besides, it exhibited positive thermodynamic parameters, indicating that the path to decomposition was non-spontaneous and unfavorable, and greater thermal stability than UHMWPE. Furthermore, the compositions prepared using CJM were more crystalline, tougher, more fracture resistant, and had higher deformation to failure than UHMWPE. Therefore, CJM serving as a method alternative to melting the UHMWPE together with PEG in the solid-state with improvements in mechanical and thermal properties at an excellent cost-benefit ratio.

Resumo em Inglês:

This study aimed to develop and evaluate chitosan (CS) and chitosan with N-Acetyl-D-glucosamine (CS/GlcNAc) sutures, comparing them to commercial Catgut sutures. Medium molecular weight chitosan was processed into sutures using the wet-spinning method, both with and without the addition of GlcNAc. The mechanical properties, surface morphology, biocompatibility, biodegradability and in vivo response of the sutures were evaluated. Scanning electron microscopy (SEM) and enzymatic degradation tests in phosphate-buffered saline (PBS) with lysozyme were conducted. Cytotoxicity was assessed using an agar diffusion assay on L929 cells. In vivo studies involved suturing rat skin, with monitoring at 5, 15 and 25 days post-surgery. Both macroscopic and microscopic analyses were performed to evaluate wound healing, tissue response, and complications. The chitosan-based sutures exhibited tensile strength within the standards for surgical sutures under dry and hydrated conditions. Particularly, the CS/GlcNAc sutures exhibited superior biodegradability, and biocompatibility compared to Catgut sutures. These sutures promoted tissue healing, reduced adverse tissue reactions and infections, and displayed non-toxic to L929 cells and favorable microbiological characteristics. Thus, CS and CS/GlcNAc sutures present promising alternatives to traditional Catgut sutures, contributing valuable advancements to the field of biodegradable surgical materials.

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Lightweight materials are required in the automotive, aeronautical, defence, marine, structural, and medical industries to increase productivity. Composites are materials that combine different alloys of aluminium, magnesium, titanium, steel, copper, and other components to initiate lightweight substitutes. The goal of the current study is to create a magnesium silicon (MgSi) alloy-based hybrid nanocomposite including silicon dioxide (SiO2) nanoparticles and graphene (GR) nanoparticles at weight percentages of 0, 4, 8, and 12 using stir casting, which is the most appropriate composite production technique. Mesquite waste from agriculture is used to manufacture the various weight percentages of SiO2 nanoparticle reinforcements. Microhardness, density, porosity, tensile strength, wear, and impact strength are among the mechanical properties that are analysed. Additionally, the characteristics of X-ray diffraction (XRD), microstructure, energy-dispersive X-ray spectroscopy (EDS), and field emission scanning electron microscopy (FESEM) are used to analyze the density, microstructure, wear, CoF, and impact strength, as well as tensile specimen fracture and EDS. Comparing the MgSi/SiO2/GR hybrid nanocomposites to the Magnesium Silicon base alloy, the results indicated a significant improvement in density, tensile strength, microhardness, wear resistance, and impact strength due to the higher SiO2 and GR nano reinforcements.

Resumo em Inglês:

Ni-Cr-based alloys are known for their high resistances to corrosive environments, high temperatures, and stresses, finding wide application in furnace systems in petrochemical plants. However, very few is known about their solidification features and how they can impact processing and properties. This study investigated the alloy solidification, obtaining a variety of as-cast microstructures in the high-Cr 28Cr48Ni5W3Co14Fe alloy. It presents results of optical, hardness, and CALPHAD analyses in a straightforward examination of solidification according to the application in the cast condition. The directional solidification setup allowed to assess a variety of samples solidified at different cooling rates, and showing different microstructural coarsening. The analyses determined secondary dendritic arm spacings (SDAS) ranging from 16 μm to 120 mm. It was determined the formation of the FCC+M23C6 quasi-eutectic constituent filling the interdendritic. An effective correlation was chosen to compute the corresponding cooling rates. Finally, an in-depth applied analysis of tube-support components for pyrolysis through cast simulation revealed the SDAS variation to be a critical feature in pre-programming casting designs. These findings play a fundamental role in advancing cast operations of heat-resistant alloy components, enhancing both quality and processing setups.

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The production systems in Campos Basin date back more than 40 years, and throughout these decades, the search for oil and gas guided operators to investigate and produce from shallow waters to ultra-deep waters. The use of normative and mandatory cathodic protection criteria, in accordance with international standards (≤ -800 mVAg/AgCl) prevents corrosion and maintains structural subsea integrity systems. According to the Brazilian Safety Management of Operational Submarine Systems (SGSS) regulation, monitored by the Brazilian National Petroleum Agency (ANP), noncompliance with the criteria requires operators to recover the electrochemical protection potential. A historical analysis of the electrochemical potentials and inspections obtained by Remote Operated Vehicles (ROV) showed the preserved state of equipment integrity, even when the protection criteria were out of range. In addition to analysis and technical reports, laboratory tests, thermodynamic simulation, and a literature review have revealed the possibility of normative criteria flexibility. This result could allow operators to significantly reduce the number of underwater interventions as well as reduce the environmental impact by reducing CO2 emissions.

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This study aimed to obtain wet-spun chitosan (CS) filaments with mechanical properties suitable for the biomaterial weaving process, in addition to evaluating the physical-mechanical and biological behavior of the CS woven meshes obtained. CS filament coagulation rate, drying methodology, and morphology were evaluated. The filament coagulation reaction was completed in 65 seconds, with a logarithmic profile, in compliance with Fick's second law. The proposed drying methodology does not cause dehydration of the chitosan saccharide rings and the stretching condition during drying modified the crystallinity index, mechanical properties, morphology, and diameter of CS filaments. The mechanical, morphological, and biological behaviors of CS woven meshes were investigated. Were observed a uniform pore size, mechanical properties in the wet state similar to those of the human dermis, controlled swelling degree, and degradation of 80% in phosphate buffered saline/lysozyme medium under 5 weeks. In addition, the CS woven meshes were not cytotoxic to L929 Mouse Fibroblast Cell Line, being promising for use as biomaterials.

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Obtaining a refined microstructure is the first step for using it in thixoforming processes. However, the chemical refining of the grain of aluminum alloys with high silicon content is impaired; therefore, grain refining via UST (Ultrasonic Melt Treatment) is a possible solution for these cases. This work aims to analyze the microstructural stability of the microstructure of the Al7Si2.5Cu alloy in the semisolid state. The material was prepared by conventional casting and submitted to processing via UST for 20 seconds with a steel horn. The material underwent reheating heat treatment for 0, 30, 60, 90, and 210 seconds under two solid fractions of 45% and 60%, respectively, 572 and 565 °C. The results show an average primary globule size of around 88 μm and a circularity form factor above 0.50. Regarding the eutectic morphology, it was quite fragmented when processed via UST; that is, the application of acoustic waves in the liquid metal causes it to mix effectively, and it is also capable of breaking the coarser Si particles. When comparing the microstructural evolution of the Al7Si2.5Cu alloy via UST with the ultra-grain refining technique, UST presents superior results in all analyzed scenarios.

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In this study, a novel SiO2/NbOx composite was synthesized through high-energy mechanical milling followed by thermal treatment, aiming to explore its effectiveness as an adsorbent for environmental remediation. The composite was thoroughly characterized using techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), nitrogen adsorption-desorption isotherms, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The XRD analysis confirmed the amorphous nature of the SiO2/NbOx composite, with a significant presence of Nb (81.1%) compared to Si (15.8%), as indicated by XRF analysis. Adsorption studies were conducted using methylene blue (MB) dye in aqueous solution, evaluating the adsorption capacity and kinetics under controlled conditions. The composite demonstrated a rapid adsorption capacity, reaching 39.32 mg g−1 in a short time, following a pseudo-second-order kinetic model. The Langmuir isotherm model fitted the adsorption data, indicating a maximum capacity of 16.7 mg g−1. The findings highlight the potential of SiO2/NbOx as an efficient adsorbent for dye removal, contributing to environmentally friendly solutions for wastewater treatment.