Resumo em Inglês:

Abstract Continuous development, improvement and innovation of ballistic material systems with superior energy absorption performance has been the subject of numerous works nowadays. Some research has been carried out with the objective of replacing traditional metallic and ceramic materials and composites with high-performance polymeric composites. Due to their excellent properties, multi-scale polymer composites have been used in the most varied segments of the industry, being recently researched in applications such as ballistic materials. This work promotes the combination of high-strength three-dimensional woven aramid fiber fabrics with vinyl ester resin to produce a panel through the compression molding process. The resin was reinforced with graphene nanoplatelets (0.1, 0.2 and 0.3% wt). The impact, tensile and flexural strength were evaluated, along with dynamic-mechanical analysis by DMA and by Hopkinson split bar test, indicating a trend of better performance for the composite containing 0.1% of graphene nanoplatelets.

Resumo em Inglês:

Abstract Although most of the studies presented in the literature are focused on MgAl2O4 formation and its role on alumina-based refractories performance, ZnO has been reported as a promising spinel inducer. Aiming to investigate the influence of ZnAl2O4 (ZA) and MgAl2O4 (MA) generation on the properties of alumina-based castables, three vibratable compositions containing calcium aluminate cement or hydratable alumina as binders and 1 wt% of silica fume, were evaluated in this work. Flexural strength, apparent porosity, hot elastic modulus, corrosion cup-tests, thermodynamic simulations, were carried out to analyze the performance of such ceramics. The results indicated that ZnAl2O4 was mainly formed above 800 °C, favoring an earlier sintering of the samples. Besides that, the softening of the castables was observed above 1200 °C, which resulted in the elastic modulus decay of the samples during their first heating cycle due to the formation of SiO2-rich liquid phase in the resulting microstructure. Cement-free samples obtained after calcination (600 °C for 5h) presented enhanced corrosion resistance when placed in contact with molten slag at 1500°C. Although, silica fume addition to the castables negatively affected their corrosion performance, it helped to counterbalance the expansion associated with the spinel and calcium aluminates formation.

Resumo em Inglês:

Abstract Silicoaluminophosphates SAPO-5 and SAPO-11 were synthesized using the hydrothermal method, 170 ºC with triethylamine and dipropylamine as the structure directing agents, respectively. This work aimed the incorporation of boron into the structures obtained by modifying the composition of the system, using as a reaction equation: Al2O3:P2O5:x SiO2: yB2O3:1,5TEA (or DPA):50H2O, with x, y=0-0.2. The phase was identified by XRD and characterized by FTIR, TGA/DTG, TPD-NH3 and nitrogen adsorption at -196°C. The structure parameters confirmed the obtaining of pure structures, showing a slight contraction in the parameters of the unit cells, indicating the presence of boron in the crystal lattice. The Brønsted sites, were modified up to a maximum of boron (y = 0.1) and for higher content, the acidity was not significant. The modification of weak acidity related to the appearance of isolated BO3 groups, indicating that the silicon atoms were not sufficiently distributed for the formation of sites.

Resumo em Inglês:

Abstract The aim of this work is to determine effective elastic properties of pultruded Glass Fiber Reinforced Polymer using micro-CT in conjunction with a two-step numerical homogenization technique. The two-step homogenization involves the segmentation of the material’s layers, which was made here by means of a machine learning approach. The segmentation was validated through the comparison between the phase’s volume fractions of samples obtained from the segmented images and laboratory tests. Further, a standard accuracy analysis in a 10-fold cross validation was performed. The samples’ effective axial Young’s modulus obtained by our numerical homogenization were compared to results obtained from experimental tests. For both the experimental tests and the image-based numerical analysis we considered samples extracted from the same profile. The two-step methodology allowed the homogenization of large volumes of the composite corresponding to the whole thickness of the profile, imaged with a high resolution. In addition to the axial effective Young’s modulus, our methodology was also able to successfully provide all the other elastic properties along the three orthogonal directions, even the ones that are arduous to be obtained in laboratory setups.

Resumo em Inglês:

Abstract Wetting of metal droplet on the solid substrate is a fundamental phenomenon which is applicable to the surface chemistry. When an oscillation field is included in the wetting condition, the wetting process shows significant advancing and receding behaviors. Also, the use of ultrasonic oscillation field is promising in welding. However, some odd morphologies led by the ultrasonic-treatment have shown wetting kinetics which have not been fully investigated. The high frequency ultrasonic vibration brings hysteresis to the contact angle, whose extra energy is attributed by the oscillation field. The ultrasonic wetting process is excited by the 20 kHz frequency periodic oscillation, during which droplet is swaying cyclically. However, after capturing the transformation of droplet morphologies, it is found that the frequency of each swaying cycle is identified to be 180 ms. Theoretical investigations have also quantitively proved that the energy for the contact angle decrease origins from the ultrasonic field, and the wettability is in a great enhancement. Thermal and kinetic effects of ultrasonic are investigated by making theoretical calculations, the 20 kHz ultrasonic field lasting for 5 seconds. Thermodynamics, vibrational mechanics, and interfacial phenomena affect the sonochemistry of wetting.

Resumo em Inglês:

Abstract In this work, a thermal plasma-based ablation test system was used to evaluate the ablative performance of the EPDM composite. The system produces a high enthalpy plasma jet generated by a plasma (DC) torch, operating at atmospheric pressure using compressed air as working gas, enabling the variation of the thermal flux concerned with the studied EPDM composites. The samples were characterized using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Fourier-Transform Infrared spectroscopy (FTIR), and Thermogravimetric Analysis (TGA) to investigate the morphology, mass-loss rate, the reaction layer (char formation), and chemical changes of the samples for each thermal flux. For a complete evaluation, the thermal fluxes were varied in 0.30, 0.45, 0.60, 0.75, and 0.90 MW/m2 and for each thermal flux, disk-shape samples remained exposed to the plasma jet for 10s. During the plasma jet exposure time, the temperatures of the surface and the back of the samples were collected to verify the formed char layer's insulator capacity and the samples' thermal diffusivity for each experimental condition. The mass loss is continuous under the thermal fluxes of 0.30 and 0.45 MW/m2, stabilizing at 60% until 0.75 MW/m2. The formed char layer begins to lose its protective capacity, evidenced by the size decrease (from 800 µm to 700 µm), due to the ablation process of the reaction layer from the thermal flux of 0.90 MW/m2.

Resumo em Inglês:

Abstract The present work is to study the production and characterization of biochar produced at two different temperatures (400 and 900 °C) and its influence on the interaction of biochar with elastomers of different polarity, aiming at the replacement of carbon black in elastomer compounds, based on the rheometric, physical, chemical and mechanical properties. The biochar production temperature of 900 ºC affected the optimum vulcanization time (t90), with compounds containing NR and NBR having the shortest vulcanization times because temperatures above 400 ºC produce an alkaline biochar that accelerates vulcanization. The biochar interacted with the two elastomers, being superior to NBR due to the oxygen concentration. Therefore, the blends with biochar showed a demonstrated reinforcement of the tensile strength, even if the biochar had a surface area of 3 m2.g-1 for the observed irregular surface, in addition to the mechanical properties, analogous to the blends with carbon black.

Resumo em Inglês:

Abstract Sustained research in high-entropy alloys (HEAs) has presented opportunities for relatively lighter alloys, specifically the Ti-containing HEAs, having an excellent combination of properties, and a great potential to replace heavier superalloys. We adopted a novel data-driven methodology to sort and select Ti-containing HEAs from the literature for their potential applications in aeroengine turbines by applying multiple-attribute decision-making (MADM). The ranks of the alloys evaluated by diverse MADMs were consistent. The data-driven methodology identified the following top five Ti-containing HEAs: ONS-BCC-Ti17.8 (Al20.4-Mo10.5-Nb22.4-Ta10.1-Ti17.8-Zr18.8), EF-BCC-Cr20-Ti20 (Ti20-Zr20-Hf20-Nb20-Cr20), ONS-BCC-Ti27.9 (Al11.3-Nb22.3-Ta13.1-Ti27.9-V4.5-Zr20.9), ONS-BCC-Ti27.7 (Al5.2-Nb23.4-Ta13.2-Ti27.7-V4.3-Zr26.2), and ONS-BCC-Ti20 (Nb20-Cr20-Mo10-Ta10-Ti20-Zr20); the methodology provides directives for further development of the identified Ti-containing HEAs for potential replacement of legacy superalloys in aeroengine turbines. The top-ranked alloy (Al20.4-Mo10.5-Nb22.4-Ta10.1-Ti17.8-Zr18.8) is lighter than the current industry benchmark, Inconel 718, by ~13%. All the top five Ti-containing HEAs have configurational entropy greater than ~13.3 J/mol K and body-center cubic crystal structure. The potency of the methodology could further be tapped by choosing appropriate weights of the properties for specific aeroengine turbine applications.

Resumo em Inglês:

Abstract Copper oxide (CuO) is a heterogeneous catalyst applied with success in several systems like vegetable oils transesterifications. The Ce-dopoing CuO is a promisor material with a potential improve catalysis performances. In this work, CuO and Ce-doping CuO were synthesized by the microwave hydrothermal method in only 5 min at low temperature (100 oC) without templates or other petroleum dependent organic substances, using only copper and cerium nitrates and sodium hydroxide as a precursors. Both materials were applied as photocatalysts for the degradation of remazol golden yellow dye (RNL). X-ray diffraction analysis showed that CuO and Ce-doped CuO has monoclic copper oxide structure without secondary phases. SEM analysis showed the Ce-doping full modify the CuO powder morphology. The dye RNL degradation rate of Ce-doping CuO was bigger than pure CuO and the expensive CeO2.

Resumo em Inglês:

Abstract The Half-Heusler semiconductor alloys can be used efficiently as thermoelectric materials to transform the waste heat into useful electrical energy. The low-cost and large-scale production of suitable half-Heusler alloys are important in the present context. In this work, a nanostructured half-Heusler NbFeSb alloy is obtained by mechanical alloying with 15h of milling. The structural parameters of the sample are investigated by powder X-ray diffraction followed by Rietveld refinement. Differential scanning calorimetry indicates that the NbFeSb phase is stable up to about 420 K. The electrical resistivity is obtained as a function of temperature. A band gap of 0.37(3) eV is obtained from UV-Vis measurements. Density functional theory calculation shows an indirect band gap of 0.52 eV. Analyses of the obtained data indicate that structural defects and nanometric crystallites sizes present in the nanostructured NbFeSb produced by mechanical alloying do not degrade the electrical and optical properties of the compound.

Resumo em Inglês:

Abstract The magnesia (MgO) hydroxylation behavior in dilute suspensions (below 50% volumetric solid loads) has been extensively studied over the past decades due to its role in refractory castables. However, its equivalent effects on concentrated systems have not been analyzed in such a systemic way, although they are known to be as or more deleterious than those observed in dilute systems. This study focuses on the hydroxylation behavior of different sources of magnesia (sinter and caustic magnesia) in aqueous suspensions prepared at various solids concentrations (17-96 vol%) and shaped by distinct methods. They were analyzed by thermogravimetry, apparent volumetric expansion measurements, X-ray diffraction, scanning electron microscopy, and in situ temperature measurements during curing. The ratio between experimental and theoretical extents of the hydroxylation degree resulted in the reaction yield. A comparison between samples containing the same water amount revealed those with caustic magnesia showed a faster evolution of hydroxylation degree, apparent volumetric expansion, and higher maximum internal temperature during curing. In both systems, the yield levels of compositions of heavier solid loads were higher, despite the small quantity of hydroxylation products formed. Significant differences in the products’ microstructure were observed and related to the ions' mobility toward crystallization nuclei.

Resumo em Inglês:

Abstract This paper presents the resistance spot welding process test and numerical simulation analysis of medium manganese steel TRIP steel (7MnSteel) and DP590 steel plate. The results show that the failure mode is PF-TT failure, and IF and PF-TT are investigated. At the same time, based on the numerical simulation under the typical welding parameters, the welding plate has the stress concentration at the electrode edge at the beginning of the welding. Along with the welding, there is the stress concentration in the heat-affected zone of the medium manganese TRIP steel, which may also be the reason for the failure of the joint here. The current density is concentrated at the contact surface between the electrode and the weld plate, and the error in the diameter of the nugget measured by simulation and experiment is within 7%, which verifies the accuracy and reliability of the model.

Resumo em Inglês:

Abstract WC-Co cutting tools are widely used by the metalworking industry. In order to improve the properties of these tools, research on the application of wear-resistant coatings, such as polycrystalline diamond, are of great importance to several applications. It is known that the occurrence of high-stress levels between the coating and the substrate can lead to adhesion failures. One strategy to minimize these failures is applying an intermediate layer of SiC. In this work, the deposition of a SiC layer was carried out by a novel two-step laser cladding approach. Instead of cladding directly the pre-synthesized SiC on the substrates, a 200 µm silicon powder layer was pre-deposited on the WC-Co substrates and then irradiated with a 30 W CO2 laser. To improve metallurgical bonding between the tungsten and the Si layer, all substrates were chemically attacked. This attack allows cobalt removal from the surface and increases surface roughness, improving the laser cladding process. After the SiC laser cladding, samples were coated with a 200 µm graphite powder layer and irradiated again by a CO2 laser. The samples were characterized by SEM, EDS, and XRD analysis. The results showed that in the first step, an irradiation energy of about 0.27 J was enough to fuse the silicon powder to the substrate and in the second step, 0.13 J was enough to promote the reaction between silicon, carbon and the WC substrate, resulting in the in-situ synthesis of SiC. Finally, a new method was proposed for the deposition of SiC on WC-Co based substrates and the observed results allowed the proposal of an empirical equation to describe the chemical reactions of the process.

Resumo em Inglês:

Abstract Biodegradability of five commercial plastic bags labelled as “biodegradable” and two referent materials were studied by a soil test for three months. As a control experiment, for studying abiotic degradation under the climatic impact (ultraviolet, temperature, and moisture) a test in a weatherometer was performed. The changes in bag samples after tests were detected by optical microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and tensile testing. It was found that all the bags may be separated into two groups: based on polyesters and based on polyolefins with oxo-additives. The second group demonstrated an ability to oxidation under UV radiation. The content of chalk filler provided a mass loss of the samples under soil and climatic tests due to its washing out. Three samples on the polyester basis filled with starch (the first group) had different compositions (polymers in the matrix were different). They showed a high biodegradability under soil conditions: mass loss was 14-21%, tensile strength decreased by more than 43%, and the surface was covered by the mycelium net. However, according to FTIR-spectroscopy, at the initial stage only starch filler biodegraded intensively, while polymer matrix was stable.

Resumo em Inglês:

Abstract The main objective of this work is to repair a structure of composite materials by gluing composite patches with different fiber directions. The effects of stress distribution, damaged area ratio, stress intensity factor KIC and imposed stacking sequence were highlighted by a comprehensive study that contained two sides, an applied experimental side and a numerical model side. The composite materials plates studied in this work are 8-layer of graphite/epoxy, glass/epoxy and boron/epoxy, with different angles. The results obtained clearly show with respect to the experimental side that the orientation of the fibers affects the ultimate strength of failure and that the fibers oriented longitudinally in the direction of the tensile strength give us an ideal performance of the composite material. As for the model aspect of this study, the effects of stress intensity factor and the relationship between the damaged area and the fiber orientation on the performance of these patches were studied. We can conclude from this study that the orientation of the fibers has an important role in the performance of the composite material and its efficiency in repair.

Resumo em Inglês:

Abstract This research work focuses on the experimental investigation of indentation damage resistance and post-indented performance of different stacking sequence of glass/epoxy laminates using mechanical and acoustic responses. The laminates with stacking sequence, namely [0]12, [0/90]6S, [+45/-45]6S and [0/+45/-45/90]3S were subjected to normal and inclined indentation with acoustic emission monitoring. Quasi-static indentation (QSI) test was conducted on the center of the laminates using a hemispherical steel indenter with 12.7 mm diameter. The residual strength of the laminates was computed by conducting flexural after indentation test. Mechanical responses such as peak force, residual dent, linear stiffness and absorbed energy were employed to assess induced damages. The results reveal that the quasi-isotropic (QIS) laminates having better indentation damage resistance under 0o and 10o loading planes, whereas the angle-ply (AP) laminates performed well at 20o. Moreover, the normalised cumulative counts, energy rate, peak frequency, AE hits and sentry function were used to evaluate the damage initiation and propagation. Further, AE results show that the shear induced damage has been reduced in AP as compared with QIS laminates under 20o indentation plane. Finally, this study concluded that the QIS and AP laminates exhibited better indentation resistance under 0o and 10o, and 20o loading planes respectively.

Resumo em Inglês:

Abstract Aluminized coatings on Ni based alloys greatly contribute to achieve process efficiency at higher operating temperatures. The present study characterized Pd-modified and unmodified aluminized coatings and compared with those of Pt-modified coatings regarding the mechanisms of formation and oxidation performance. The results show that Pd reduces the driving force for diffusion of Al during coating formation, increases outward diffusion of Ni and reduces diffusion of alloying elements (Cr and Ti) into the intermetallic layer. In contrast, Pt increases the driving force for diffusion of Al and the mobility of Al in the intermetallic layer of the aluminized coating. These characteristics have a direct impact on oxidation at 1000 °C that showed that Pd reduced the rate of θ-Al2O3 → α-Al2O3 transformation, accounting for higher density of voids at the interface β-(NiAl)/θ-Al2O3, diffusion of oxygen into the coating, spalling and faster degradation of coatings.

Resumo em Inglês:

Abstract This study presents the development of niobium carbide cermets bound to nickel and Ni-12Al (wt%). The use of Ni-12Al (wt%) and Ni aims to replace strategic elements such as cobalt (Co) utilized in tungsten carbide-based cermets. Cermets of different compositions were processed by conventional powder metallurgy. Microstructural analysis with semi-quantitative chemical analysis by EDX, Vickers microhardness and density measurement were performed to evaluate the influence of high energy milling application and sintering temperature on the properties of these cermets. A milling time of 20 min in a planetary mill and sintering temperatures of 1420 ºC or 1450 ºC resulted in homogeneous microstructures, densities close to 90% and hardness of around 1000 HV1, showing a potential for use of this material in cutting tools.

Resumo em Inglês:

Abstract Metal additive manufacturing is rapidly developing technology, but its application in wider scale is limited by several factors. One of these is expensive raw material, because it requires certain physical properties. Two most popular metal additive manufacturing methods are printing from powder and printing from wire. Wire is usually produced by drawing it from rod. Rod can be produced by directional solidification, which is well known method to study the microstructure formation depending on various parameters during solidification. In this study directional solidification of A360 aluminum alloy with electromagnetic interaction is investigated. Aluminum alloy is induction melted and then directionally solidified into the rod 12-20 mm in diameter. Aim of this work is to investigate the role of axial DC magnetic field and electric current interaction on the grain refinement and mechanical properties of A360 aluminum alloy. It is found that electromagnetic interaction can be the approach to refine the grains, regulate the growth of oriented columnar grains and to improve mechanical properties of the material.

Resumo em Inglês:

Abstract The cold roller die process increases the tensile strength and decreases the ductility of steel wire. Annealing heat treatment is applied to restore mechanical properties, but this is a costly process. This research shows that it is possible to control the mechanical properties of ultra-low carbon steel wire inducing the Bauschinger effect and relieving residual steel stresses. The present study uses several pulleys to promote and control the Bauschinger effect magnitude through alternated cyclic bending. A Completely Randomized Design, a regression study, and the Akaike Information Criterion were used to understand the relationship between the quantity and diameter of pulleys and the influence on the magnitude of the Bauschinger effect. Statistical models showed that it is possible to have a maximum increase of 103% in uniform elongation and a maximum decrease of 14% in yield strength. An interaction between the factors studied in controlling the Bauschinger effect magnitude was confirmed.

Resumo em Inglês:

Abstract In this study, green high-density polyethylene (GHDPE) composites with 5, 10 and 15% natural powdered cork (CP) with and without 5% maleic anhydride (PE-g-MA) were developed in order to evaluate the potential of these materials for civil construction applications. The composites were produced in a co-rotating twin-screw extruder and injection molded. An impedance tube was used to determine the acoustic behavior of the composites, which were then used as ceiling tiles in prototypes of provisional constructions in order to study ascertain their performance with respect to thermal comfort in the City of Teresina, PI - Brazil. Our data indicates that composites sound absorption coefficient values are good between 500 and 1200 Hz, especially for those with a higher percentage of cork, with the lowest absorption rate observed for composites containing PE-g-MA. The composites used in the prototypes provided a decrease in the internal temperature of the built structure.

Resumo em Inglês:

Abstract High entropy alloy is a multi-component alloy material with equal or near atomic number, which has excellent wear resistance and corrosion resistance. In this paper, AlxFeCoCrNiMn (x = 0,0.5,1.0,1.5) high entropy alloy cladding layer was prepared by laser cladding on Q345 steel plate. The phase structure, microstructure, hardness and wear resistance of the cladding layer were studied. The results show that the cladding layer of AlxFeCoCrNiMn alloy has good metallurgical bonding ability with Q345 steel. The cladding area is mainly columnar and equiaxed. The cladding layer of AlxFeCoCrNiMn alloy is mainly composed of BCC + FCC solid solution phase, which is caused by the addition of Al element under the high entropy effect. Al element promotes the formation of BCC phase structure. With the increase of Al element, the hardness of cladding layer increases. The hardness of A1.0 cladding layer is 670HV, which is close to three times of Q345 steel. When Al (x = 1.0), the hardness of the cladding layer is the highest, and it also shows better wear resistance with lower friction and wear loss.

Resumo em Inglês:

Abstract Glyphosate affects ecosystems due to exposure of non-target crops and is a persistent contaminant at low concentrations. The application of palygorskite to reduce glyphosate contamination in Brazil is an environmentally friendly way to remediate impacted areas. This research evaluated palygorskite application for glyphosate adsorption present in a synthetic effluent. Palygorskite samples were ore dressed by wet granulometric classification and wet magnetic separation and submitted to organophilization with cetyltrimethyl ammonium bromide solutions at concentrations of 0.01, 0.1, 1.0 and 1.5% (w/w), and the organo-palygorskite was applied in glyphosate adsorption tests. After ore dressing there was an increase in its cation exchange capacity from 19 to 41 meq 100 g-1 and the surface area was 149 g m-2. The 1.0% organo-palygorskite adsorbed about 86% of glyphosate from synthetic aqueous effluent. Based on this high adsorption yield, the organo-palygorskite is a potential adsorbent for remediation of effluents containing the toxic herbicide glyphosate.

Resumo em Inglês:

In the present study, tensile properties, plastic flow behaviour and impact toughness of Nickel free High Nitrogen Austenitic Stainless Steels (NFHNSS) were evaluated under solution annealed and aged condition (at 700 oC, 800 oC and 900 oC for 14 hours). Plastic flow behaviour was analyzed using Holloman and Ludwigson flow equations. Samples in solution annealed and aged conditions exhibited a flow transition behaviour. Ludwigson flow equation produces best fit for flow transition behaviour. Transmission Electron Microscope (TEM) investigations of NFHNSS samples after tensile test revealed dislocation network and planar arrangement of dislocations adjancent to Grain Boundaries (GB) in the solution annealing and aged conditions respectively. Plastic deformation of NFHNSS occurs by a combination of planar glide and twinning. Impact energy was significantly higher in solution annealed condition than aged condition. Impact energy values decreased with increasing aging temperature. Precipitation and growth as well as morphology of Cr2N at the GBs reduce the impact energy values significantly. Presence of larger precipitates readily pull out from GB easily than smaller precipitates at low temperatures. Large precipitate, at the GB’s readily pull out at low temperature, compared to slower ones.

Resumo em Inglês:

Abstract The present study investigated the effects of the addition of the TiO2 nanoparticles with different weight percent on the copper nanocomposites' abrasive wear behavior. In addition, optimal machine learning regression (OMLR) methods are used to detect the copper nanocomposites' abrasive wear behavior. The powder metallurgy method is used to fabricate the Cu/TiO2 nanocomposite specimens with 0, 4, 8, 12 wt% TiO2. The abrasive wear behavior of fabricated specimens is evaluated experimentally using a pin on the desk apparatus. The abrasive wear results are used to predict the abrasive wear behavior of the fabricated composites using OMLR methods. OMLR methods are implemented and carried out using MATLAB/software. The OMLR methods use the input parameters of TiO2, sliding distance and load, and the weight loss due to abrasive wear as an output to build their optimal models. OMLR methods were successfully detected with small errors, especially GPR methods. The results of the proposed GPR were compared with those obtained from the ANN model with the efficacy of the GPR model. The experimental results demonstrated that the weight loss in test specimens decreased with increasing wt% of TiO2 addition. This reflected improvements in the wear resistance of copper nanocomposites compared to pure copper.

Resumo em Inglês:

Abstract When ice forms on solid surfaces, it can cause issues in many different sectors (aircraft, electricity lines, etc.). Surfaces and coatings with hydrophobic qualities may be used in anti-icing applications. The purpose of this work is to utilize RF Magneton Sputtering to deposit AZO thin coatings, which will slow the accumulation of ice on the surface. The effects of changes in argon partial pressure on the anti-icing, wettability, optical, and structural properties of the resulting thin films have been experimentally investigated. X-ray diffraction demonstrated a (002) peak of ZnO, the intensity of the peak diminishes with an increase in partial pressure. The band gap was measured to be between 2.98 and 3.15 eV, and the average maximum transmittance was observed to be around 82% for 50% partial pressure and 71% for 33% partial pressure, confirming the transparency of the thin films. Wettability studies revealed that the films are hydrophobic with a maximum contact angle of 127.5°, which was deposited at lower partial pressure. Films deposited at 33% partial pressure delayed the formation of ice on the surface by 4.5 folds when compared to an uncoated substrate.

Resumo em Inglês:

Abstract The industries that have polymers as an important raw material in their production, such as the construction, automotive, electrical and electronic sectors, always seek innovations to cut costs, reduce weight, easiness of processing, maximizing mechanical properties, and recyclability. In this context, this work presents the study of the kinetic parameters and viscoelastic behavior of a new thermoplastic system initially liquid. Through differential scanning calorimetry (DSC) analysis, Brookfield viscosimetry; dynamic-mechanical analysis (DMA) and mathematical modeling with consolidated and standardized methods, it was possible to evaluate the polymerization kinetics and viscoelastic behavior of the material in solutions with different concentrations. The generated equations allow the prediction of the kinetic and gelation behavior of the material reducing the need for laboratory tests to determine polymer properties. The found results showed that concentrations of benzoyl peroxide initiator with 1wt% in the methyl methacrylate (MMA) copolymer solution have the best viscoelastic and dynamic-mechanical properties with a less expensive polymerization cycle.

Resumo em Inglês:

Abstract Kenaf polypropylene composites with high fiber load of 85 wt% were produced using glycerine as a processing aid and maleic anhydride-grafted polypropylene (MAPP) as a compatibilizer/coupling agent. Commercially available MAPPs with different molecular weights and anhydride contents were used to determine what properties of the MAPPs were important to achieve high mechanical properties of these highly filled composites. A homo-polymer and a random-polymer, were compared as matrix polymers. Composites were produced using a high-shear kinetic mixer followed by compression molding at pressures ranging between 345 and 5520 kPa. The data suggests that adding MAPPs with a low molecular weight and high anhydride content at concentrations of 5 wt% resulted in composites with the highest mechanical properties. The authors suggest that a combination of a high surface area, low viscosity and high anhydride content of the MAPP are resulting in a good stress transfer between fibers and matrix polymer.

Resumo em Inglês:

Abstract The past two decades have witnessed prompt advances in aluminum alloy welding methods. Friction crush welding (FCW) has been recommended to be one of the key solutions to join these particular alloys with a range of plate thickness. This study aims to contribute to this welding technique by conducting several experiments to investigate the effect using three traverse speeds (120, 140, and 160 mm/min); and two rotational speeds (1400 and 1500 rpm) on the produces joint. These parameters were considered in a welding 1145 Aluminum sheets with 1mm thickness. The produced joints were evaluated using optical micrographs, micro-hardness, SEM, and tensile tests properties. The results showed that the best joint has 41 MPa tensile strength, 24 HV micro- hardness, and the best microstructure were obtained at 1400 rpm rotational speed and160 mm/min traverse speed.

Resumo em Inglês:

Abstract In this paper, ultrasonic surface rolling processing (USRP) was used to strengthen GCr15-bearing steel. A finite element three-dimensional model of USRP was established to analyze the residual compressive stress and equivalent plastic strain distribution on the bearing steel surface. The microstructure, hardness, surface roughness, and corrosion resistance before and after USRP treatment were characterized by SEM, EBSD, X-ray diffraction (XRD), and electrochemical techniques. Results indicated that USRP treatment can significantly improve the material's surface microstructure and residual compressive stress distribution and obtain a plastic strain layer of about 60μm. After USRP treatment, the Kernel Average Misorientation (KAM) increased, and the dislocation activity was more intensive, resulting in aggregation near grain boundaries, and the percentage of LAGBs increased to 38.8%. Under the combined effect of surface grain refinement, residual compressive stress, and high glossy surface, the self-corrosion current density is reduced by two orders of magnitude, and the corrosion resistance is significantly improved. This investigation suggests a solution to the bearing failure problem and has implications for understanding the deformation mechanism of ultrasonic surface rolling processing.

Resumo em Inglês:

Abstract This study is based on the numerical simulation of the mechanical response of yttrium-stabilized zirconia ceramic (3Y-TZP) dental implants as a function of their intrinsic geometry and masticatory loads. Samples (n=20) of 3Y-TZP ceramics were compacted, sintered at 1500 °C - 2h, and characterized by relative density, X-Ray diffraction (XRD), and scanning electron microscopy (SEM). The elastic parameters (modulus of elasticity and Poisson ratio), used in the numerical simulations, were measured by the Impulse Excitation Technique, and the bending strength was obtained using piston-on-three-balls testing. An authorial implant design and, comparatively, commercial implant CAD models were used in this study as an initial geometry of dental implant in a typical adult mandible anatomy. From CAD and CAE techniques, finite element models were generated for all implant geometries. Loading cases were considered based on different intensities (100N to 500N) and orientation angles (45° or 90°) to reproduce the human masticatory efforts. The numerical predictions were compared with finite element simulations of gold-standard titanium-based implants. The investigated 3Y-TZP sintered ceramics presented high densification (> 99%), with a microstructure formed by submicron equiaxed tetragonal zirconia grains. The 3Y-TZP average bending strength obtained from piston-on-three-balls testing is 1192 ± 99 MPa. For both dental implant geometries, the zirconia implants showed average strength of less than 550 MPa, which, in turn, is independent of the masticatory load value or orientation angle. All finite element predictions are 50% inferior to the corresponding measured flexural strength values and preliminarily enable the 3Y-TZP ceramics for dental implant applications without fracture risk.

Resumo em Inglês:

Abstract One typically characterizes the transformation kinetics of a parent phase, α, into a single phase, β, by measuring the volume fraction transformed, VVβ, against time. Sometimes one also reports the interfacial area density between the new and the parent phase, SVαβ, against the volume fraction transformed. SVαβ is a dynamic interface. It migrates as the growth of the new phase takes place. Interfaces between transformed phases might be called static interfaces. These may be present before transformation starts, for example, grain boundaries of a polycrystalline parent phase. Alternatively, static interfaces, SVββ, may appear during the transformation because of impingement. Therefore, one may better understand the microstructural evolution following the behavior of the volume fraction, dynamic and static interfaces. A more complicated situation occurs if the parent phase transforms into two or more product phases, for example, α→β,γ. In this work, we apply parameters to describe the transformation of a parent phase into a single phase, the contiguity and the dispersion, to the situation in which the parent phase transforms into two or more phases. We tested these parameters against computer simulations and concluded that they combine a good description of the behavior of the simulated transformations and simplicity.

Resumo em Inglês:

Abstract Materials produced by additive manufacturing (AM) have been extremely related to literature. However, there is still unconsolidated knowledge about the fatigue life and respective mechanisms of initiation of cracks predominant in the VHCF regime for these materials. What has been observed in materials produced by conventional routes is that fatigue cracks tend to nucleate from intrinsic defects of the material located internally or in subsurface regions. The change in the evolution process of fatigue cracks leads to the formation of a characteristic morphology on the fracture surface, known as “fish-eye”. Another widespread aspect observed on the fracture surfaces is the formation of a fine granular area (FGA) nearby the initiation sites. This work aims to investigate the mechanisms of crack nucleation in VHCF of two distinct materials: conventional steel, DIN 34CrNiMo6 and AISI 316L stainless steel produced by L-DED. The ultrasonic tests were carried out at a frequency of 20±0,5 kHz and R= -1. The S-N curves were obtained and fracture surfaces were analyzed, fish-eye and FGA formation was verified. FGA sizes were compared to values estimated by empirical equations. FGA and fish-eye sizes were related to stress amplitude and maximum stress intensity factor (SIF).

Resumo em Inglês:

Abstract Due to their biodegradability, affordability, low density, and numerous other benefits, natural fiber polymer composites are preferable to conventional GFRP in maritime applications. However, when exposed to moisture, their mechanical qualities deteriorate. A significant agricultural waste called pineapple leaf fiber (PALF) can be employed as reinforcement in epoxy matrices. Improved interfacial bonding between phases improves interfacial bonding and hence enhance mechanical and water absorption properties. Only evaluation of mechanical properties is undertaken in this paper. Nanoclay in 1.5 and 3 wt% was incorporated in epoxy resin via magnetic stirring and ultrasonication. PALF fibers were subjected to NaOH treatment and was analyzed using SEM and FTIR techniques. Hand layup and compression moulding were used to fabricate composites using a nanoclay-epoxy resin combination and chemically treated PALF (20 & 30 wt%). The combination of 30 wt% PALF and 1.5 wt% nanoclay results in the maximum mechanical properties, namely tensile and flexural properties. The results of SEM investigation of fractured specimens show that interfacial bonding in epoxy composites containing PALF is poor while that in epoxy composites containing PALF and 1.5 wt% nanoclay is excellent. Due to nanoclay agglomerations, bonding is inadequate at 3 wt% nanoclay, which lowers the mechanical properties.

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Abstract High-carbon structural steel wires were prestressed to various levels in a plasma hydrogenation environment and then pulled in a slow strain rate test (SSRT). The effect of plasma hydrogenation under different prestressing levels on the material's tensile response and hydrogen embrittlement was noted. It was found that the ultimate tensile strength (UTS), yield strength, and ductility of the steel wire samples are decreased by plasma hydrogenation and prestressing levels. The more drastic decrease in the UTS, yield strength, and ductility is found in the plasma hydrogenated prestressing steel to a higher prestressing level. Moreover, the hydrogen embrittlement index of the steel wire samples is significantly increased by plasma hydrogenation and prestressing level. The highly plasma hydrogenated prestressing steel wire samples exhibit complete brittle fracture. A mixed mode of fracture, i.e., ductile and brittle, was observed at the surface of the plasma hydrogenated prestressing steel wire samples at lower levels. The hydrogen embrittlement areas at the fracture surfaces of steel wire samples are observed to increase with plasma hydrogenation and prestressing levels. More severe hydrogen cracking and blistering resulted in the fracture surfaces of plasma-hydrogenated prestressing steel wire samples with higher levels.

Resumo em Inglês:

Abstract In this paper, on the basis of first-principles, the CASTEP module of Materials Studio is used to calculate the band structures and optical properties of CuFeSe2 and CuFeS2 under the PBE pseudopotential of the generalized gradient approximation (GGA). The calculated results show that both CuFeSe2 and CuFeS2 are direct bandgap semiconductors with forbidden band widths of 0.64 eV and 1.06 eV, respectively. In the visible light range, the highest absorption coefficient of CuFeSe2 is 1.082×105 cm-1, the average reflectivity is 0.52, the maximum conductivity is 7.23 fs-1, the electrostatic constant is 65.9; the maximum value the highest absorption coefficient of CuFeS2 is 0.872×105 cm-1, the average reflectivity is 0.44, the maximum conductivity is 4.44 fs-1, the static dielectric constant is 52.32. The calculation results in this paper show that compared with CuFeS2, CuFeSe2 has advantages in photoconductivity and carrier separation, but has disadvantages in band gap and reflectivity. It is recommended to combine the two materials to prepare tandem solar cells.

Resumo em Inglês:

Abstract Three different Heat Affected Zones (HAZ) in hot rolled Nickel Free High Nitrogen Stainless Steels (NFHNSS) based on three different peak temperatures were physically simulated using Gleeble Simulator to investigate microstructural evolution and structure-property correlation. Optical microscopy revealed that the austenite grains are recrystallized in the simulated heat affected zone in the peak temperature range of 750 oC to 1050 oC. Extent of recrystallization of grains and nucleation of precipitates varied with peak temperatures. TEM characterization showed the presence of Cr2N precipitate having an average particle size in the range of 300 nm to 395 nm in the simulated HAZ were confirmed by Selected Area Electron Diffraction (SAED) analysis. Precipitation kinetics of Cr2N were simulated using Thermo-Calc were found to correlate well with experimental values. Mechanical properties of specimens taken from three different HAZ were evaluated for tensile strength and hardness. Variation in strength of the different specimens has been discussed using various strengthening models. Fractography analysis was also carried out to understand the effect of peak temperature on fracture behaviour. Transition in fracture patterns in NFHNSS from ductile to mixed mode was observed for different specimens.

Resumo em Inglês:

Abstract The current investigation presents the wear-worn surface analysis of a silicon carbide-reinforced brass-based composite synthesized by stir casting. Wear behavior of the brass composite pin was analyzed by disc tribometer. Wear characterization studies and confirmation of elemental composition are investigated through scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) respectively. The worn surface of the synthesized brass composite was analyzed using atomic force microscopy (AFM). The aim of the investigation is to examine the surface morphology of the worn specimen. Based on the input constraints, the wear rate ranges from 0.0135 to 0.0893 mm3/min. The applied load is the predominant factor in the wear rate (83.75%). Sliding velocity has a minor effect on wear rate (1.06%). The improved surface roughness of 15.27 nm was produced on the worn surface. The novelty of the research work is to study the various surface parameters of the worn surface, such as roughness average, root mean square roughness, maximum height of the roughness, skewness, and kurtosis. These parameters were analyzed at different wear-worn surfaces of the synthesized brass composite. The wear-worn surface was deeply investigated and incorporated with SEM and AFM analysis.

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Abstract The laser welded joint of 2000MPa cold rolled annealed hot pressed steel (PHS) is easy to break during cold rolling. In this paper, the laser welding method is used to butt weld four kinds of PHS2000 with a thickness of 3.5mm. The four kinds of PHS2000 steel are added with elements of 0% Nb, 0.04% Nb, 0.06% Nb + Cr and 0.08% Nb + Cr. The microstructure of the four kinds of welded joints is compared and analyzed. The mechanical properties of the four kinds of joints are compared through hardness test and tensile test. The results show that after adding 0.04% Nb, residual austenite appears in the weld zone and fully quenched zone, the width of columnar crystal decreases, the average hardness of the weld zone decreases from 595HV to 408HV, and the tensile strength increases from 608MPa to more than 800MPa. For chromium containing steel, the increase of niobium content can reduce the size of columnar crystal in weld zone.

Resumo em Inglês:

Abstract The development of additive manufacturing (AM) technology provides higher feasibility for designing and manufacturing lattice structures. However, the manufacturing process usually generates residual deformation and stress, and even produces cracking, thus affecting the performance of the parts. This work establishes a simulation model of the Ti-6Al-4V lattice structures during laser powder bed fusion (LPBF) based on the inherent strain method. Effects of geometric lattice parameters (inclination angle, rod diameter, rod length) on the residual deformation and stress are analyzed. Based on the simulation results, measures for improving the quality of the lattice structures are proposed. The proposed model and simulation results can provide theoretical references for designing and manufacturing the lattice structures during practical engineering applications of LPBF.

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Abstract The continuous casting tundish is the last metallurgical reactor where molten metal flows before solidifying in the continuous casting mold. A tundish covering powder can be used for improving steel cleanliness; in this case it is named ‘active tundish slag’. The objective of this work is to evaluate, in laboratory, the effect of three kinds of tundish covering powders on cleanliness for a SAE 1055 modified steel - a Ca-aluminate, a Ca-Mg-aluminate, and an Al-silicate powder, analysing their interaction with rice hull ash. The forementioned materials were molten on liquid steel, representing different kinds of tundish covering powders which are used in the steel industry: a Ca-Mg-aluminate, an Al-silicate, and a Ca-aluminate. Experiments were performed with and without a top layer of rice hull ash, simulating industrial conditions. Distribution, density, and mean diameter of inclusions were measured through automated inclusion analyses. Through computational thermodynamics it was possible to evaluate deviation from saturation (considering Al2O3 and MgO from refractory) and slag viscosity. It can be stated that the Ca-aluminate tundish covering powder gives better results regarding cleanliness for the SAE 1055 modified steel under laboratory conditions.

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Abstract The Artificial Neural Network (ANN) techniques were utilized to predict wear rate and CoF of the Ti-5Al-2.5Sn matrix reinforced with B4C particle manufactured by the powder metallurgy. TMCs and wear test samples were characterized by the Scanning Electron Microscope (SEM). Dry sliding wear narrative of the composites was estimated on a pin-on-disc machine at various loads of 20-60N, sliding velocity of 2-6m/s and sliding distance from 1000m-3000m. The wear rate of the composite was reduced by augmentation in weight fraction of boron carbide from 3-9%. The benefits of interfacial TMCs with B4C are: increase in strength, wear-resistance, and volume fraction. ANN was planned and utilizes a Levenburg-Marquardt program algorithm to reduce the mean squared error using a back-propagation technique. The input parameters are considered to include load, sliding velocity, and sliding distance. The experimental results of an ANN model and regression model are compared. ANN replicas have been urbanized to foreshow experimental rate of wear and CoF of TMCs and examined that ANN predictions have exceptional concord with deliberated values. Accordingly, the prediction of wear rate and CoF of TMCs using ANN in earlier actual manufacture will significantly save the manufacturing time, exertion, and expenditure.

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Abstract Strong acids used in industrial applications as cleaning, descaling, among others, can severely damage metallic structures, requiring corrosion inhibitors to diminish or avoid these issues. Since many conventional compounds used for this purpose may result in environmental and human health issues, eco-friendly compounds such as Schiff bases have been recently investigated. The synthesis of three novel Schiff bases (SBs) was confirmed by infrared spectroscopy (FTIR) and hydrogen nuclear magnetic resonance (1H-NMR). Weight loss measurements were carried out in 1 M HCl over 303K-333K. Furthermore, the combination of these compounds with a surfactant improved the efficiencies, reaching an efficiency of 93%. Optical and scanning electron microscopies confirmed the reduced roughness and pit depths of carbon steel samples. Density-functional theory calculations for neutral forms of SBs revealed that the geometrical and the energetical parameters are similar for the three studied SBs. The geometrical results exhibited more planar structures of protonated species, improving the chemical and physical interactions between aromatic rings and metallic atoms.

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Abstract Usually, scraps of X22CrMoV12-1 alloy are obtained through machining of steam turbine blades and recycled through casting. However, this process is considered too costly. The viability of recycling X22CrMoV12-1 scraps with addition of vanadium carbide (VC) through powder metallurgy was analyzed in this study. Scraps of X22CrMoV12-1 alloy with VC were milled in a planetary ball mill during 10, 30 and 60 hours. The granulometry of the powder was determined through laser granulometry. The evolution in particles morphology and amorphization was conducted using scanning electron microscope (SEM) and x-ray diffraction (DRX) techniques. Stress-strain curves were obtained through compressive strength test. The results indicated that the best milling condition found was 60 hours. Also, the X22CrMoV12-1 alloy with VC addition produced by powder metallurgy showed good mechanical strength. Thus, this route was considered promising to reshape this material with smaller energy involved in the process.

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9/65/35 PLZT relaxor was studied under a bias electric field using the acoustic emission method. It was established that the temperature of smeared dielectric constant maximum exhibits the V-shape, lying fully within the ergodic phase, as well as that the threshold electric field is found to be approximately the same as in both PMN-0.24PT and PFN-0.02PT relaxors. A reason of the latter phenomena is discussed from the viewpoint of incorporated ions properties.

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In this work, biodegradable biocomposites were developed using PLA/PHB blend as matrix and two types of microcrystalline cellulose as filler at three different contents. The biocomposites were evaluated regarding their thermal and morphological characteristics and molecular dynamic behavior. It was seen that cellulose addition did not promote significant changes in the Tm, Tc and Tcc in the matrix. On the other hand, XRD and TGA revealed that the addition of the highest content (7 wt%) of cellulose fillers resulted in a more significant decrease in crystallinity and thermal stability of the PLA/PHB matrix, suggesting a formation of filler aggregates. This indication was confirmed by TD-NMR, whose results pointed to a greater heterogeneity molecular in the samples containing higher cellulose contents. Therefore, this technique proved to be a relevant and complementary tool for the characterization of composites materials, contributing to determinate the most appropriate filler content introduced in a polymer matrix.

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Green materials have received great interest in wide industrial applications due to their desired properties. However, the reinforcing conditions have a significant impact on how they perform in their final use. The current study intends to statistically examine the effects of three key parameters on the average tensile strength of polypropylene composites. These factors included the type of fiber, the chemical treatment, and the fiber's weight percentage. The fibers were hemp and sisal, and the weight percentages were 10, 20, and 30. While some of them received sodium hydroxide (NaOH) treatment, the rest were left untreated. The main effect and the interaction effect were both examined using the analysis of variance (ANOVA). The findings demonstrated that, on average, the weight percentage had no tangible effect on the tensile strength of polypropylene (PP) composites. Additionally, the performance of sisal and hemp composites was unaffected by treatment. The strength, however, is significantly influenced by the type of fiber. The investigation also showed that there was little difference between untreated hemp and untreated sisal in terms of tensile strength.

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This study aims to contribute to the scientific knowledge by investigating the influence of build direction and post-curing on the material and part attributes of acrylonitrile butadiene styrene (ABS-like) like resins by photopolymerization based additive manufacturing (AM). Specimens were manufactured in different build directions with the parameters that offer the highest density. Two groups of specimens, one as-built and the other post-cured, were subjected to dimensional inspections, surface characterization, fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), hardness measurements, tensile tests, bending tests, Charpy impact tests and the obtained values were reported and benchmarked. It has been observed that the change in the build direction significantly affects the surface roughness and the average surface roughness of the samples produced in the vertical plane is much higher than those produced in the horizontal plane. It was demonstrated that post-curing has a negligible effect on part dimensions and density. It increases hardness, tensile modulus and flexural modulus while reducing elongation and impact resistance. The effects of post-curing on chemical and thermal properties were also compared and it was determined that it improves the thermal stability. In the absence of post-curing, vertical as-built specimens were observed to have higher strength than their horizontal counterparts.

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The use of alternative raw materials is essential for establishing a circular economy in the mineral and ironmaking sectors. Therefore, this study investigates the potential of lime sludge as fluxing material during pelletization and proposes an alternative route for the usage of waste. The pellets were manufactured with different binary basicity values (CaO/SiO2) (0.15-0.45) and bentonite (0.5-0.7 wt%) and fixed carbon (0.5-1.1 wt%) contents. The results demonstrated that lime sludge has significant potential for application in pelletization. Pellet quality was evaluated using drop number, mechanical strength, tumble index, porosity, and kinetic analyses. Pellets with the optimal composition using lime sludge withstood 3.6 drops/pellet, a tumble test of 1.57 wt.%, and a mechanical strength test of 214.83 kgf/pellet and exhibited a porosity of 31.28%. Lime sludge did not influence the reducibility of the iron-ore pellets. In the temperature range of 800-900 °C, the reaction was controlled by diffusion, with Ea between 179.89 and 233.10 kJ/mol.

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The macroscopic properties of composite materials depend on the microscopic properties of the constituents and the geometric arrangement of their phases. Therefore, it is essential to predict heterogeneous materials’ mechanical properties by simulating microstructural finite element models. The present article aims to analyze particle reinforced composites composed of spherical alumina inclusions surrounded by a glass matrix using a tridimensional representative volume element. Herein, microstructures are artificially created considering a regular or random arrangement of the inclusions. Two materials systems previously studied in the literature were analyzed. The discretization of the models was performed to have periodic mesh, thus enabling the use of periodic boundary conditions. A finite element model is created using Abaqus software. Numerical results show that the macroscopic properties can be estimated with high accuracy for the temperature where linear matrix behavior stands. The predictions were compared to experimental data from the literature. The models with a regular arrangement of inclusions show a difference inferior to 10%, while random arrangements show a difference inferior to 3.9%. The developed numerical algorithms can be modified to include new features, such as other dispersed phase arrangements or nonlinear material behavior.

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In the present work, the AZ61 alloy, one of the most important commercial structural magnesium alloys, was anodized in three different alkaline electrolytes consisting of 3 M KOH + 0.15 M Na2SiO3 + 0.1 M Na2B4O7.10H2O, 3 M KOH + 0.5 M Na3PO4 and 3 M KOH + 0.50 M Na2SiO3. The treatment was conducted at two different current densities, 20 and 30 mA.cm-2 for 10 minutes. The anodized layers were characterized by scanning electron microscopy, X-ray diffractometry and X-ray photoelectron spectroscopy. The corrosion resistance was assessed by potentiodynamic polarization tests. The SCC behavior was studied using slow strain rate tests in 0.1 M NaCl solution at room temperature. Conventional tensile tests were also conducted in air. The susceptibility to SCC was dependent on the morphology of the anodized film. The composition of the electrolyte and the current density of the anodization treatment affected the SCC susceptibility of the AZ61 alloy. The best corrosion resistance and the lowest susceptibility to SCC were obtained for samples anodized in the borate-containing electrolyte at 30 mA.cm-2. The smooth and compact surface morphology of the anodized film obtained in this condition was the main reason for the improved SCC behavior of the AZ61 alloy.

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The Digital Image Correlation (DIC) technique is an important method of evaluating material strain fields. Composite materials have inherently heterogeneous elastic properties, in the function of the different phases present in the composition, whereat the traditional techniques of deformation evaluation may not be sufficient to determine the mechanisms that eventually contribute to the failure of the material. The present work were evaluated, the tensile mechanical properties of polyester matrix composites loaded with an industrial residue of red mud, with a mass fraction of 20%. The properties were surveyed using the conventional technique of strain gauge and compared with the data obtained through DIC. The results showed that the DIC technique was accurate in monitoring the displacements and determining the average deformation of the tested specimens, in addition to providing ample deformation fields, for the evaluation of failure mechanisms throughout the sample request process.

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In this work, plasma nitriding (PN) and cathode cage plasma deposition (CCPN) treatments were carried out with temperatures of 400 and 450 °C to evaluate the modifications caused on the surface of pure niobium samples. XRD, SEM, Vickers microhardness, and sphere-disk analyses were used to characterize the coatings’ composition, morphology, hardness, and wear resistance. The results showed that the treated samples increased hardness and wear resistance, with the sample submitted to CCPN at 450 °C presenting the best tribological behavior.

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The bottleneck of hemicellulose as a bio-based material is its processability and property drawbacks (softening and hydrophilicity). Thus, mixing other biopolymers can be an alternative. This article proposes blending hemicellulose (10−50 wt%) with polyhydroxybutyrate (PHB) and poly (lactic acid) (PLA), using acetic acid and chloroform as casting solvents to improve its processability and thermal properties. The materials were thermally (TGA - thermogravimetric analysis), chemically (FTIR - Fourier transformer infrared) and morphologically (SEM - scanning electron microscopy) characterized. Finally, a multicriteria decision analysis (MCDA) evaluated the materials’ properties to identify the optimum combination (casting solvent, biopolymer and hemicelluloses proportion) for producing an optimal blend. The MCDA established that the blend of hemicellulose:PHB (10:90 wt/wt) produced with acetic acid was optimum considering melting temperature and the crystallinity criteria. Moreover, higher hemicellulose concentration in the blends decreased the MCDA success rate, indicating the worst properties. PLA blends showed a higher degradation temperature than PHB. The PHB blends produced with acetic acid demonstrated improved properties when compared to chloroform, revealing its potential as a solvent.

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The development in current manufacturing technology entails better wear resistance materials. Inthis study, ZK60A Mg alloy matrix composites reinforced with x wt.% (x = 0, 4, 8 and 12 wt.%) of TiN powders are developed through powder metallurgy (PM) route. The tribological behaviour of the composites under dry sliding conditions was estimated using Pin-on-disc instrument. The influence of the control parameters such as wt.% of TiN, applied load , sliding velocity and sliding distance on the wear rate and co-efficient of friction were analysed using Taguchi coupled grey relational approach GRA and L16 orthogonal array is selected for performing design of experiments. The lowest WR of 0.01147 mm3/m and 0.2446 COF formed at 12 wt.% of ‘R’, 9.81 N of ‘P’, 5.24 m/s of ‘V’ and 1000 m of ‘D’. From Analysis of variance (ANOVA), the wt.% of TiN powder (P = 82.68%) was observed as a primary factor controlling the WR and COF of composites. Finally, confirmation trials were performed to validate the results. SEM examination ensures homogeneous disbursement of TiN powders in the matrix alloy. Addition of reinforcement results in increase in density and porosity. The higher hardness observed at 12wt.% TiN incorporated Mg alloy composite.

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This work presents a two-step procedure to obtain thin films with a combination of CuSbS2 and Cu12Sb4S13 phases for study in thermoelectric applications. The procedure consisted of the physical evaporation of sulfides layers (Sb2S3 and CuS) on glass substrates and the subsequent annealing of the samples in a N2 atmosphere. The characterizations by Raman spectroscopy and XRD revealed that the samples presented a varied percentage of Cu12Sb4S13 and CuSbS2. The results indicated that the percentage of phases depended on the initial thickness of the sulfide layers and the annealing temperature. The lower initial ratio between sulfide thicknesses and annealing temperature above 300 °C favored the formation of Cu12Sb4S13. However, the thermoelectric properties were improved when the phases coexisted in the thin film compared to samples with high percentages of Cu12Sb4S13. In this way, a sample with a power factor of 2.30 μW /cm∙ K2 at 60 ºC was identified.

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In this paper, the multi-layer multi-pass welding process was used to weld 115mm 08Cr9W3Co3VNbCuBN (G115) steel pipe, the gas tungsten arc welding (GTAW) was used in root pass welding, subsequent welding by dynamic hot wire gas tungsten arc welding (TIP TIG) welding method, while the post-weld heat treatment (PWHT) of 770°C × 10h was carried out afterward. The microstructure and mechanical properties of different zones of the welded joint were analyzed by OM, SEM, XRD, microhardness and impact tests. The results showed that the ferrite and martensite were observed in the weld metal (WM), the fine-grained heat-affected zone (FGHAZ) and the coarse-grained heat-affected zone (CGHAZ) consisting of prior austenitic grain boundaries (PAGBs) and martensite, and more precipitates including coarse M23C6 carbides with fine MX-type carbonitrides were observed inside the grain boundaries and grains. The hardness distribution patterns along different locations (Cover, Fill, Root) on the welded joint cross-section were the same, from base metal (BM) to WM hardness gradually increased, and WM hardness was the highest. WM impact toughness was worse than HAZ, impact fracture mode was a mixed tough-brittle fracture but biased towards brittle fracture.

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The automotive industry is one of the largest industrial segments in the world market. The exhaust system of motor vehicles is responsible for the emission and treatment of toxic gasses released by the engine. In this sense, the application of titanium on an AISI 1020 steel substrate was carried out by plasma deposition using a cathode cage. The aim of this research was to evaluate the application of this material in the exhaust system of motor vehicles. The samples were characterized by scanning electron microscopy (SEM), confocal microscopy (CM), microhardness tests and corrosion resistance tests. The samples exhibited a thin film with higher titanium content and hardness than the uncoated sample. The corrosion potential also increased and the current density was lower than the uncoated sample. The conclusion is that the deposition of thin titanium films on AISI 1020 steel with CCPD has the potential to produce thin films.

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Poly(vinyl chloride) (PVC) is considered one of the most versatile polymers due to its interaction with different additives. On the other hand, binary sulfides have wide applications as zinc sulfide (ZnS), one of the first discovered semiconductors. This study aims to synthesize a nanocomposite material containing nano ZnS in the PVC matrix with a surfactant as a compatibilizer agent to evaluate its optical and electrical properties when exposed to gamma radiation. Our results showed that adding ZnS at 0.5 wt% concentration in the PVC matrix promoted the system from insulating to the semiconductor material. Therefore, gamma radiation has played an important role in nanocomposites' optical and electrical properties with changes in electrical and electrical conductivity, constant dielectric parts, refraction index, optical band gap, and Urbach energy. Thus, our study points to the development of nanocomposite material, semiconductors, and features useful for applications in flexible electronics or optical-electronic devices.

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The optoelectronic properties of dye zinc and titanium-based metal-organic framework (MOF) compounds with regard to their application as photo-anode material characterized in solar cells were investigated. Analyses of the optoelectronic properties were performed on the MOF single crystal unit cell with adsorbed dye to determine the electronic and optical properties of the relevant materials. The electronic and optical properties were predicted by density functional theory (DFT) calculations. The results show that the absorption of light occurs for the examined MoF compounds from the near UV to the (visible) blue spectral range, at optical band gap sizes from 2.8 eV up to 3.88 eV. Dye sensitization of MOF with eosin Y or crown ether gave additive UV-Vis spectra. An improvement in band gap or an improved electron injection could be archived as well. Moreover, the light absorption does not solely depend on the linkers used, but also from the metal atoms in the secondary building unit. The fluorescence of MOFs depends on the linker and especially on the linker coordination and their rotation relative to each other. The utilizations of MOFs and their derivatives as electrodes, photoactive materials, charge carriers and additives in different solar cells are highlighted.

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Numerical simulation was used to predict the thermal behavior and the resulting microstructure at the heat-affected zone (HAZ) of a 170 mm diameter and 3.5 mm thickness super duplex stainless steel (SDSS) UNS S32750 tube. In order to evaluate the thermal response from the model, a usual welding situation involving interpass temperature (IT) and its influence on the HAZ microstructure was exploited. Thus, two superimposed autogenous welding passes were simulated, the first clockwise with the tube in the room temperature and the second, counterclockwise, with the tube at the temperature of 250oC. Even subjected to successive thermal cycles and high interpass temperature, the proportion and morphology of the phases at the HAZ and Fusion Zone (FZ) did not present significant differences when comparing the two welding passes. Meanwhile, nitrogen losses should be avoided during welding in order to obtain a balanced microstructure in DSS welds, contributing to guarantee satisfactory toughness in addition to resistance to pitting corrosion. The predictions from the simulation were validated by using experimental results obtained from the autogenous TIG (Tungsten Inert Gas) process.

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Superhydrophobic surfaces of conventional Ti-6Al-4V (TC4) titanium alloys facilitate drag reduction and anti-wear. However, the economical fabrication of a wear-resistant superhydrophobic Ti-10V-2Fe-3Al (TB6) titanium alloy for application in modern aerospace equipment remains to be achieved. Here, an efficient wear-resistant superhydrophobic TB6 titanium alloy surface using commercially available materials and processing equipment was fabricated through nanosecond laser texturing and facile chemical modification. The wettability of textured surfaces, including line and grid patterns, ablated at different laser scanning intervals were investigated and analyzed in terms of surface morphology and chemical composition. Moreover, the mechanisms of coefficient of friction changes on different surfaces under dry and water sliding conditions were studied based on surface morphology and wettability. Under dry sliding and water lubrication conditions, the average coefficient of friction of the prepared superhydrophobic surface can be reduced by 29% and 74%, respectively, compared with that of the original hydrophilic surface.

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This study focused on the effects of different peak (austenitizing) temperatures (Tp) over the martensite start temperature (Ms) and its influence on the final residual stresses after welding simulation. For this purpose, the expansion coefficients obtained through physical (dilatometric) simulations of a high-strength low-alloy steel were considered for three peak temperatures: 1300 °C, 1150 °C, and 920 °C and a cooling rate of 25 °C/s. Aiming at clarifying the physical phenomenon behind GTAW welding, one carried out nonlinear transient thermomechanical finite-element (FE) analyses to reconstitute the welding process and simulate the subsequent formation of residual stresses in the HAZ. Once the heat source simulation was calibrated, four material models were created, one for each Tp, and a fourth model considering a constant expansion coefficient, without considering the martensite transformation for comparison. A Three-bar model was evaluated to isolate the effects of Tp (Ms) in the residual stresses. A composite plate model was also considered, in which the sheet HAZ was subdivided according to the reached peak temperature, and the respective material models were applied. The results show the importance of martensite transformation on the welding-induced residual stress and a clear trend of decreasing tensions with lowering the Tp, especially over HAZ.

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In this work, iron chloride (FeCl3.6H2O), a single reagent, was used to create the phases of hematite (α-Fe2O3) and akaganeite (β-FeOOH) without the need of organic solvents using the microwave-assisted hydrothermal technique (HM). X-ray diffraction demonstrated the efficacy of the HM technique in the generation of crystalline phases of α-Fe2O3 at 180oC and β-FeOOH at 120oC. The development of pseudo-cunic and stick-like particles was a result of changes in experimental variables, which also had a substantial impact on the materials structural characteristics. The nitrogen (N2) adsorption/desorption isotherms of the samples containing akaganeite and hematite phase resembled those of mesoporous materials. Hematite has a surface area of 25.44 m2 g-1, while akaganeite has a surface area of 110.60 m2 g-1, according to the calculation. Thermodifferential and thermogravimetric techniques were used to assess thermal degradation. The use of microwave hydrothermal synthesis was promoted as being quick, easy, affordable, and safe for the environment.

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We have synthesized ZnO nanostructure by using two-step methods i.e ultrasonic nebulizer and chemical bath deposition (CBD) at 95oC for two hours. The morphology, structural, reflectance, and photoluminescence properties have been characterized by the scanning electron microscope (SEM), the X-ray diffraction (XRD) measurement, ultraviolet-visible (UV-Vis) spectrophotometer, and photoluminescence spectrometer, respectively. Structurally, all samples possess polycrystalline hexagonal wurtzite structure, and the addition of Al-Cu decreases the crystallinity of ZnO nanostructures. Meanwhile, morphologically, the role of Cu dopants in Al-Cu co-doped ZnO nanostructures suppressed the growth of nanostructures in the c-axis. Hence, it can be used to modify the morphology of ZnO nanorods to nanodisks/nanosheets. Optically, the Al-Cu co-dopants can be used to shift the optical band gap energy of ZnO nanostructures to a lower wavelength (blueshift). The photoluminescence (PL) properties confirmed that the Al-Cu co-dopants have two peaks at the photon energy of 3.78 eV and 3.90 eV.

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Currently, the overheating detection of electric system components is performed using thermal imaging devices, which depend on on-site regulation parameters, require skilled operators and suitable weather conditions. The development and application of innovative technologies to monitor hotspots has highlighted the use of sensors based on thermosensitive materials. In this study, a temperature sensor with thermochromic coating was developed. Thermochromic sensors covered with a varnish layer and nano-titanium oxide, in addition to thermochromic paint, were produced. A 23 experimental design was established to assess the performance of thermochromic sensors under artificial weathering conditions. Color measurements of the coatings were performed using the CIELAB method. Fourier-transform infrared (FTIR), UV-Vis (Ultraviolet-Visible), (thermogravimetric TGA, and Differential Scanning Calorimetry (DSC) analyses were performed on the sensors exposed to photodegradation to detect changes in the thermochromic coatings. The sensors exposed to thermodegradation, and salt spray weathering showed ΔE (total color difference) values below 1.50 points in the presence of TiO2. In comparison, the sensors exposed to photodegradation showed ΔE values above 10 points, and UV-Vis analysis revealed changes in the chemical structure of the coatings. These results demonstrate that the varnish layer and TiO2 can help minimize the degradation effects of temperature, light, and salinity.

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This paper investigated how casting affects ASTM ZA-27 alloy's tribological performance in dry and lubricated conditions. To this end, varying contact loads and sliding speeds were applied to tribological tests. The ZA-27 alloy was produced using gravity die casting (GDC) and new rheo-casting (NRC) methods. The results showed that the microstructure of GDC ZA-27 alloy is dendritic containing α and η phases. While the NRC alloy microstructure demonstrates a semi-globular structure of fine equiaxed α phase bordered by eutectoid α and η. The NRC alloy achieved an improvement in tensile, hardness, and elongation properties by almost 15%, 20%, and 25%, respectively. Regarding tribological properties, the NRC alloy achieved an enhancement in tribo-behavior by lowering the coefficient of friction (COF) to about 67% than the GDC alloy. Further, the results showed that the wear rate recorded an increment with applied load for both GDC and NRC alloys. Though, the results showed that the wear rate with NRC alloy was lower compared to the GDC alloy with about 84% at 160N normal load. The worn surfaces of NRC alloys were characterized by smooth and shallow wear grooves. While the GDC alloy worn surfaces were rougher and experience deeper grooves and damage.

Resumo em Inglês:

Boron-manganese steel 22MnB5 is extensively used in structural automotive components. Knowledge about its microstructural evolution during hot stamping and resistance spot welding (RSW) is extremely relevant to guarantee compliance with application requirements. Particularly, corrosion properties are critical to the application of uncoated sheet steels. However, microstructural studies are usually simplified to top-hat geometries, which might not be fully representative of the complex thermomechanical cycles locally faced by a real component. Therefore, the present work brings an extensive characterization of a hot-stamped 22MnB5 automotive B-pillar in terms of microstructure, hardness and corrosion resistance, which were correlated with a reverse engineering of the process using numerical simulation. Physical simulations of the subcritical heat affected zone (SCHAZ) of RSW were done to assess the influence of microstructure on martensite tempering. Results showed that the component undergoes a complex strain distribution along its body during hot stamping. Most heavily strained regions presented higher amounts of ferrite, leading to poorer corrosion resistance, since ferrite behaves as an anode. Physical simulations of the SCHAZ showed that the softening degree due to martensite tempering is solely affected by peak temperature, while other microstructural features appear to exert negligible or no influence.

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The demand for new advanced high strength steels (AHSS) has been increasing in the last few decades. A large part of this demand comes from automotive companies. We have produced a new complex-phase (CP) steel with 1200 MPa of mechanical resistance and 8% of elongation, called CP1200. In this paper the dilatometric and microstructural characterization of a newly produced CP1200 steel is presented. The new steel was produced by making changes to the heat treatment of the already industrially available CP1100. The microstructure was quantified using light optical microscopy (LOM) and electron backscatter diffraction (EBSD). The microstructure of both steels was compared to identify the origin of the mechanical properties improvement. A new microstructure distribution, with higher amount of bainite and smaller concentration of ferrite and martensite was identified.

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Ca3Co4O9 powders and ceramics were synthesized and sintered using microwave-assisted heating method.Another batch of powders was calcined by the conventional heating method and this powder was used to produce ceramics sintered by microwave sintering aiming to compare with those prepared by microwave method. The formation of the phases based on calcination method and time was assessed by X-ray diffractometry. The synthesis and sintering methods affected various properties of the ceramics, including grain size, density, phase amount, Seebeck coefficient, thermal conductivity and electrical conductivity. Microwave heating method reduced the time required for the powder synthesis and sintering of ceramics. Ceramics produced using powder obtained by the conventional method presented Figure of Merit (ZT) values of approximately 0.04. However, these values were reduced for the ceramics produced by microwave heating reaching a value of about 0.02. The evaluation of the thermoelectric properties of the Ca3Co4O9 ceramics suggests that the main issue to enhance the Figure of Merit of the CCO ceramics is related to density and Ca3Co4O9 phase amount present in the ceramics.

Resumo em Inglês:

Bacterial infections after implant surgical procedures are a complication observed in many surgeries to treat bone injuries or diseases. Bacteria can attach to the surface of the implant producing biofilms, and if treatment with antibiotics does not work, further surgery is necessary to remove the infected implant. Among the biomaterials for bone implants, bioceramics based on calcium phosphates (CaPs) such as β-TCP stand out, due to their chemical similarity with bone and high bioresorbability. β-TCP has the characteristic of easily accommodating in its crystalline structure reasonable amounts of doping elements, such as monovalent and trivalent ions, which makes it an efficient transporter of drugs, molecules, and therapeutic ions The objective of this work was the incorporation of bioactive glass (BG 45S5) via sol-gel and silver nanoparticles (Ag-NPs) in β-TCP scaffolds, aiming to confer antimicrobial activity to the scaffolds, without prejudice to biocompatibility. XRD and FT-IR analysis indicated structural changes after the incorporation of BG 45S5 and Ag-NPs in β-TCP scaffolds, and these compounds induced the partial transformation of the β-TCP phase into α-TCP phase and the formation of sodium-calcium silicates and silver silicates. The FT-IR spectra showed characteristic bands of α-TCP after incorporation, in addition to the predominant bands of β-TCP. Biocompatibility after incorporation of BG 45S5 was improved, with a significant increase in cell viability. After the incorporation of Ag-NPs, cell viability was maintained at an acceptable level, no cytotoxic behavior was observed, and the scaffolds showed antibacterial and antifungal activity. The results indicate that BG 45S5 and the Ag-NPs incorporated showed a synergistic behavior, conferring antimicrobial activity to the scaffolds without compromising biocompatibility, showing great potential for applicability in tissue engineering.

Resumo em Inglês:

The use of biogenic residues to obtain calcium phosphate compounds, mainly hydroxyapatite (HAp), is an excellent alternative to reduce costs in obtaining biomaterials. The purpose of this study was to obtain hydroxyapatite from fish bones and hen eggshells by alkaline hydrolysis and precipitation, respectively, and compare them to HAp obtained from calcium commercial source based on physical-chemical properties and in vitro assays. The biomaterials obtained were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET) method and Fourier Transform Infrared Spectroscopy (FTIR). The XRD results revealed the presence of the main characteristic peaks of single HAp phase and FTIR analysis showed various functional groups, such as PO43-, CO3-2 and OH-, confirming the presence of HAp. SEM observations of the synthesized HAp showed a rod-like and spherical-like morphology. The cell viability and bioactivity of the materials were evaluated by rezasurin reduction and McCoy medium assays, respectively. The biomaterials obtained had no toxic effect and the sample obtained from fish bone was more bioactive when compared to the others. Therefore, the biowastes can be used as an alternative source of calcium in the synthesis of hydroxyapatite with promising properties for application in the biomedical area.

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The aerospace industry is constantly looking for innovative materials that exhibit good mechanical and corrosion properties. The 2198-T851 (Al-Cu-Li) alloy was developed to replace the conventional Al-Cu-Mg in aircraft structures. Despite the usefulness of the 2198-T851 alloy, its performance may be affected when subjected to an aggressive medium containing chloride ions. The deposition of Nb2O5 coatings by using the reactive sputtering technique on the 2198-T851 alloy surface appears as a powerful tool to improve the corrosion resistance of this material. Recently, groundbreaking research findings have demonstrated the positive effect of Nb2O5 coatings on corrosion protection of alloy 2198-T851. However, the corrosion products originated from the 2198-T851 aluminium alloy are poorly understood. The use of Raman spectroscopy and XPS techniques may help to shed some light on the corrosion products of 2198-T851 alloy. Results demonstrated the corrosion products are mainly composed by CuCl2 x H2O, CuCl, Cu2Cl(OH)3, Al(OH)3, and AlO(OH).

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Thin films of titanium aluminum nitride (Ti(1-x)AlxN) were deposited on silicon, copper, and plasma nitrided AISI D2 tool steel substrates through reactive direct current grid-assisted magnetron sputtering. The depositions were performed in the metal and compound modes using nitrogen flow rates of (7.2 ± 0.1) sccm and (6.8 ± 0.2) sccm, respectively. The relations between the process parameters and the crystallographic orientation were investigated. Chemical and mechanical properties were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and instrumented indentation technique (IIT). X-ray diffraction spectra and electron diffraction patterns revealed the presence of a Ti(1-x)AlxN phase with a face-centered cubic structure in both films. In metal mode, the coatings exhibited a preferential (111) plane orientation, changing to (200) in the compound mode. The change in preferential orientation was influenced by the reactive gas partial pressure.

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The study presents CeO2 particles synthesized by the microwave-assisted hydrothermal method using different synthesis times for the analysis of sensitivity to carbon monoxide gas, aiming at its application as a sensor material to prevent poisoning caused by this highly toxic gas. Structural, morphological and spectroscopic and electrical behaviors were analyzed by X-ray diffraction, Rietveld refinement, transmission electronic microscopy, Raman scattering spectroscopy, optoelectronic characterization chamber and FT-IR. The samples presented fluorite-type cubic structures, increase in crystallinity and particle size with the variation synthesis time from 5 to 8 minutes. From the micrographs it was observed that the nanoparticles initially were spherical with a surface domain (200), and the synthesis time made them cubic/polyhedral with a surface (111), showing differences in defects and influencing in its properties. The sample synthesized at 8 minutes showed the best result with response and recovery time of 16 and 2 seconds, respectively, at 390 °C, therefore promising for the fabrication of CO gas selective sensing device.

Resumo em Inglês:

Hydrogen embrittlement (HE) in API 5L X70 steel was investigated by testing notched and unnotched uniaxial tensile specimens and single-edge tension specimen, SE(T). Apparent hydrogen diffusivity (Dapp = 1.4 x 10-10 m2/s) and solubility (Sapp = 4.9 mol H/m3) were determined by electrochemical hydrogen permeation tests. Through mathematical fitting, it was possible to separate the strong traps present at the beginning of the first permeation curve (φ = 0.43 mol H/m3). Uniaxial tensile tests showed a loss of ductility of up to 33% in the hydrogenated condition. Fracture mechanics tests exhibited a toughness decrease of 14% after exposure to hydrogen. The high resistance to HE was presented suggesting that these microalloyed steels can solubilize hydrogen in the matrix with low segregation, reducing the impact on embrittlement. A mix of ductile and quasi-cleavage fracture was observed in the hydrogenated samples with an increased stress triaxiality.

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The polycrystalline CdS/CdTe thin film solar cell is one of the most important photovoltaic devices for cost-effective generation of solar electricity for terrestrial applications. A typical superstrate structure of CdTe solar cell has been studied through current-voltage (J-V) and secondary ion mass spectroscopy (SIMS) measurements. A close correlation between quality of interphases and its photovoltaic efficiency was determined. It was found an improvement of open circuit voltage (VOC) and efficiency associated to CdS and CdTe thermal treatments, and a reduction of diffusion of S and Cd into CdTe and CdS respectively. An efficiency of 12% has been reached on solar cells with a Te and ZnTe interlayer as part of the back contact. Low diffusion of Cu along absorbent material was observed when Te and ZnTe was used creating a stable back contact along the time. Diffusion and intermixing at each junction SnO2:F/CdS, CdS/CdTe and CdTe/Te or ZnTe/Cu/Au was found, establishing limit values of element diffusion along CdTe solar cells.

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In many applications, such as fuel storage tanks and fuel lines, galvanized steel is used as a construction material which comes into contact with biodiesel. Considering that biodiesel is more corrosive than petroleum diesel, studies that aim to increase the corrosion resistance of galvanized steel in this environment are required. The present work investigates how the chemical conversion treatment in the oxalic acid solution affects the corrosion resistance of galvanized steel in soybean biodiesel (B100) in the absence and presence of the natural additives the extract the turmeric, clove, ginger, stone breaker, and rosemary. The results obtained indicate that the conversion treatment reduces the corrosion rate of the zinc coating in soybean biodiesel in the absence and presence of additives, and in this condition the effect of the conversion treatment depends on the additive used.

Resumo em Inglês:

AISI 6160 steel is used to manufacture cutting blades and springs due to its high tensile strength and good ductility. However, it has low mechanical strength and low wear resistance. In this work, a duplex treatment consisting of CCPD followed by PN was performed to improve the surface properties of the steel. In addition, XRD, optical microscopy, microhardness, and sphere-disk tribological analysis were used to verify the surface changes of the samples. The results showed a significant improvement in surface hardness and better wear resistance of AISI 6160 Steel submitted to Duplex treatment. The sample submitted to the CCPD treatment for 4 hours and, after nitriding at 500 °C for 2 hours, presented higher surface hardness and wear resistance than the sample only subjected to plasma deposition, characterizing the efficiency of the use of the duplex treatment adopted in the present work.

Resumo em Inglês:

Magnesium phosphate cement are materials prepared by reacting magnesium oxide with water-soluble phosphates such as mono-ammonium dihydrogen phosphate, which solidified at ambient temperature through the formation of hydrated phases in the material. However, MgO has a high reactivity and requires calcination to reduce its surface area, facilitating the practical application of magnesium phosphate cement. Because it is a process with large energy consumption, the sintering cost is very high when implemented at a large scale. Since the final stages of solid-state reaction are rarely reached, the addition of some components is beneficial from a calcination point of view, as they can lead to the formation of low melting liquid phases. In this study, effects of the inorganic activation of MgO on the properties of cements in terms of phase formation, microstructure, setting time, pore size distribution and mechanical properties were evaluated. The additivation considerably improved the properties of MgO powders, and Na2O-PbO-SiO2-Bi2O3-B2O3 was the most efficient additive to reduce de BET surface area (about 5-6 times). Cements produced using doped MgO without calcination at high temperatures or the use of higher levels of retarding and dispersing additives, showed better physical (porosity approximately 5 times lower and density approximately 38% higher) and mechanical properties (approximately 9 times higher) than the pastes produced with MgO calcined without additives (traditional method).

Resumo em Inglês:

In this study, a hydroxyapatite (HA) coating derived from the scales of the Amazonian fish pirarucu (Arapaima gigas) was produced using calcination at 500 and 750 °C and deposited on AISI 316 stainless steel substrate using the process of thermal spraying, high velocity suspension plasma spray (HVSPS). To verify its potential, this material was characterized by X-ray diffraction (XRD), by which characteristic peaks of hydroxyapatite were evidenced. Via X-ray fluorescence (XRF) of the samples, it was observed that the Ca/P ratio was equal to 2.00. Using the Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy, it was possible to observe the characteristic bands of the HA. For the coating, the mechanical nanoindentation test showed mean Vickers microhardness (VH) values of 93.25 VH for the hydroxyapatite and of 196.57 HV for the substrate. The modulus of elasticity (EIT) was 77.85 GPa for the hydroxyapatite coating and 136.45 GPa for the substrate. Optical microscopy showed that the coating was homogeneously deposited.

Resumo em Inglês:

This work reports on the properties of GaN films grown by reactive magnetron sputtering onto glass substrate kept at relatively low temperature (400°C), using different RF power applied to the Ga target. Their structural, morphological, vibrational and optical properties were characterized by X-ray diffraction, atomic force and scanning electron microscopies, Raman spectroscopy and UV-vis spectrophotometry. The films have wurtzite phase with strong preferential orientation in the c-axis direction. Moreover, two clear contributions to the (0002) diffraction peak could be found, indicating the presence of two different morphologies, which were discussed in terms of the formation of an intermediate layer between the substrate and a dominating columnar-like microstructured film.

Resumo em Inglês:

Optimally designed bone implants with a suitable porous structure have similar mechanical properties to bone tissue and at the same time have good biocompatible and excellent bioactivity. The preparation of medical biological porous scaffolds by metal 3D printing technology is one of the most promising and attractive biomedical applications. The traditional regular porous and self-growing porous scaffolds were established by using CAD and C4D software, and the different scaffolds of three-dimensional models in similar porosity was obtained. A three-dimensional model of a scaffold with a porous structure was designed, and the porous scaffold was prepared by selective laser melting (SLM) technique, and its microstructure and mechanical properties were analysed. Under the similar porosity, the average hardness of the surface of the self-growing structure porous scaffold reached 236.5HV, and the stress at 5% compressive strain after heat treatment was close to 75 MPa. The original surface of the 316L porous scaffold made by SLM has the potential to effectively promote the differentiation of MG63 cells into osteoblasts. At the same time, the surface morphology and structure of the self-growth scaffold are similar to human cancellous bone, which is conducive to cell attachment and growth, so it is more suitable for repairing diseased parts of human bones.

Resumo em Inglês:

Aluminium metal matrix composites are highly dominated composites for various applications such as military, marine, aircraft, aerospace and automobile because of their corrosion resistance, tribological and mechanical properties. In this research, aluminium alloy 5032 composite reinforced with SiCnp (4, 8, 12 and 16 wt.%) was manufactured using stir casting method and subjected to various mechanical, metallurgical and wear tests. The novelty of this research lies in the fabrication and characterization of Al5032/SiCnp composites, which has been not done before. The Energy Dispersive X ray analysis (EDAX) was used to examine the presence of SiC in Al5032 matrix and Scanning Electron Microscope (SEM) was employed to examine the microstructure of the composite. Further micro hardness, wear resistance, tensile and impact tests were carried out. The aforesaid properties increases upto 12 wt.% addition of silicon carbide in Al5032 alloy and thereafter reduces. The nanocomposite Al5032/12wt.%SiC exhibits 98 HV, 256 MPa tensile strength, 19 MPa impact strength and 5 mg wear loss.

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Coating of stainless steel (SS) plays a crucial role in improving the properties required for various biomedical applications. These characteristics include biocompatibility, mechanical along with corrosion and wear performances. In this respect, this study developed uniform pure hydroxyapatite (HA) and HA/ titania (TiO2) composite films applied on the surface of SS using the sol-gel technique. The morphology and chemical composition of investigated surfaces were analyzed using a scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS), respectively. Moreover, uncoated and coated SS substrates' surface roughness, micro-hardness, and wear characteristics were evaluated. The results displayed that a homogeneous nano-scale surface with higher values of micro-hardness and wear resistance is obtained for coated SS substrates, especially for HA/TiO2 composite coating.

Resumo em Inglês:

In this study, alkaline treatment was used to change the surface of the new beta titanium alloy Ti25Ta25Nb3Sn and enhance its bioactivity. Ti25Ta25Nb3Sn, a new experimental alloy was processed in the laboratory and the surfaces were modified using alkaline treatment. Samples were soaked at 60 0C for 24 hours in different NaOH solutions to obtain surfaces with different morphologies. The surfaces were characterized by different techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and Atomic Force Microscopy (AFM). The wettability of the surfaces was measured using the sessile drop method. In vitro studies were carried out to evaluate cell adhesion, proliferation, and bacteria adhesion. As a result of the alkaline treatment, a nanoporous and amorphous layer was formed on the Ti25Ta25Nb3Sn alloy surface with super hydrophilic behavior for all conditions evaluated. However, different nano topography was observed which affected biological response. The morphology obtained after immersion in 1.5 NaOH solution led to bacteria adhesion decreased and osteoblasts cells differentiation. Results of this study show that is possible to obtain a new titanium experimental alloy with excellent bulk and surface properties that may decrease the risk of infections and increase osseointegration.

Resumo em Inglês:

This study is focused on the performance evaluation of flash-butt-welded rail joints concerning their mechanical strength and fatigue life. Residual stresses created in the heat-affected zone were measured and the effects of the welding process and notch sensitivity on the fatigue behavior in the weld region were experimentally assessed. Aiming at clarifying the physical phenomenon behind the flash-butt welding, nonlinear transient thermomechanical finite-element analyses were performed to reconstitute the welding process and to simulate the subsequent formation of residual stresses. A new hypothesis for explaining higher temperatures in the rail web than in the rail foot and head was suggested and numerically verified. Experimental fatigue results showed high notch sensitivity and highlighted the effects of microstructure variations on the fatigue life. In general, a good agreement was achieved between numerical and experimental measurements of residual stresses, which was essential for understanding the fatigue phenomenon and the formation of residual stresses in flash-butt-welded rail joints. A relevant outcome is the simulation of the hot burrs from the welding process as prescribed heat inputs on a convenient part of the rail surface. This simulation strategy has shown adequate to explain the non-uniform temperature changes and the corresponding originated residual stresses.

Resumo em Inglês:

Automotive industry is searching for new ways to improve vehicles’ energy efficiency through mass reduction, using aluminum alloys. This change requires a surface protection to extend the life cycle of the components and aluminum anodization is the most used solution. This research is focused on the intake and exhaust ducts’ surfaces of aluminum internal combustion engines cylinder head, which are subject to chemical agents and temperature variation. To extend the working life of this component it is necessary to obtain a covering protective layer. The process targeted the anodization of an internal surface of a much larger part of a cast aluminum-silicon alloy cylinder head. The anodization was obtained using a H2SO4 solution (184 g.L-1) and a DC voltage starting at 20 V. The Al2O3 layer obtained, inside the cylinder head´s ducts, has an average thickness of 120 µm in accordance with the proposal of providing a suitable surface protection.

Resumo em Inglês:

Aluminium (Al) has low strength, limiting its applicability for certain technical applications seeking higher mechanical strength and deformation resistance. Integration of ternary hybrid reinforcement in Al offers a compelling opportunity to achieve a synergistic combination of multiple desirable properties opening new avenues for advanced engineering applications beyond what can be achieved with mono or binary reinforcement systems. Here, Al-based nanocomposites were developed by incorporating a ternary hybrid reinforcement system, consisting of graphite nanoplatelets (GnP), hBN and MWCNT. Al-1 wt.% GnP0.3CNT0.3hBN0.4, Al-2 wt.% GnP0.3CNT0.3hBN1.4, Al-3 wt.% GnP0.3CNT0.3hBN2.4, and Al-5 wt.% GnP0.3CNT0.3hBN4.4 nanocomposites were developed by powder metallurgy (PM) route. The results indicate that the Al-1 wt.% GnP0.3MWCNT0.3hBN0.4 hybrid nanocomposite exhibits the highest wear resistance. Among the hBN-based nanocomposites, Al-3 wt.% hBN nanocomposite exhibited the best wear properties. Increasing the hBN loading level in the CNT-GnP-hBN ternary nanofiller system beyond 0.4 wt.% resulted in a deterioration of physical, mechanical and wear properties. Al-1 wt.% CNT0.3GnP0.3hBN0.4 hybrid nanocomposite had the highest relative density and hardness of ∼92.56% of ∼415.91 MPa respectively. The compressive strength (σmax) of Al-1 wt.% CNT0.3GnP0.3hBN0.4 hybrid nanocomposite was ∼874.77 MPa, while the σmax rapidly declined in the nanocomposites with the increased content of the CNT-GnP-hBN hybrid nanofiller.

Resumo em Inglês:

In this study, the effects of incorporating recycled photopolymer-plate residues from a packaging flexography process into polyester-glass fiber composites were examined. Ternary composites with an unsaturated polyester matrix with elastomer particles from recycled photopolymer-plate residues were evaluated using two types of glass fibers: in the forms of a fabric with bidirectional fibers and a blanket with multidirectional fibers. The composites were prepared by hand lay-up lamination using different rubber contents (0, 2.5, 5, and 10 wt% based on the polyester resin mass fraction), and were characterized for their void content, flexural and impact strengths, and dynamic mechanical properties. Primary results indicated that the incorporation of the rubber particles increased the difficulty of lamination, while promoting greater void formation with higher filler content. The rubber particles decreased the impact resistance properties but did not reduce the flexural strength or storage modulus, indicating that despite the elastomeric composition, this residue from the photopolymer plates showed a reinforcing rather than toughening character.

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Flow is central to the operation of wells and pipelines and can be postulated to govern the formation of protective corrosion product layers, which is critical to overall infrastructure integrity. However, the phenomena involved remain poorly understood. Therefore, the main objective of this work was to investigate the effect of flow on the heterogeneous precipitation of FeS and FeCO3 as corrosion products on mild steel. Initial corrosion studies were conducted in an autoclave stirred by an impeller. The tests were conducted under quiescent and dynamic conditions for 24 h in an aqueous brine (10 wt.% NaCl, 120°C, 5 bar CO2, 0 and 10-3 mol/l Na2S2O3). The experimental results showed that the increase in rotation speed did not prevent the formation of FeS or FeCO3 crystals. Having confirmed the presence of corrosion product layers, the differences in the trends in corrosion rates may result from the diffusion barrier presented by these layers.

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The use of thin films as solid lubricating makes it an excellent option for controlling wear and friction under certain operating conditions, in addition to not harming the environment. Thus, this work aims to study plasma deposition with a cathodic cage of MoS2 thin films on AISI 1020 steel substrates. From the adaptation of the cathode Cage named cathode cylinders, the samples were treated in cathodic and floating potential with temperatures of 300 °C, 350 °C, and 400 °C in an argon atmosphere. After the treatments, they were subjected to chemical analysis by X-ray diffraction (XRD) and Raman spectroscopy, in addition to a calotest tribological test. Also, it was possible to quantify the coating thickness using scanning electron microscopy (SEM). In general, the results indicated success in the deposition of molybdenum disulfide in all samples treated at fluctuating potential, as it is possible to visualize in the XRD since it indicated the presence of peaks referring to MoS2 and its compounds, in addition to an expressive reduction in wear through the calotest test.

Resumo em Inglês:

Zn-Ni alloys have been used to decrease the corrosion rate of carbon steel substrates. These are used in applications such as bolt coatings, threaded parts, swift valves for gas pipelines, aircraft landing gear, brake system components and others. Zn-Ni coatings containing nanocrystals of cellulose (CNC) obtained from sisal fiber (Sif), a natural polymer, were manufactured using the electroplating technique. Obtaining the nanocrystals involved bleaching raw sisal fiber and then acid hydrolysis to extract the nanocrystal. The effect of the concentrations of the CNC-Sif (0% v/v, 2%v/v, 3%v/v, and 4%v/v) on the morphology and microstructure of the Zn-Ni coating was analyzed through Scanning Electron Microscopy (SEM), X-ray diffraction, and roughness measurements using confocal microscopy. The effect of the addition of CNC-Sif on the efficiency of galvanostatic deposition was analyzed. The corrosion rate through mass loss and electrochemical tests were also analyzed. The effect of adding CNC-SIF on coating microhardness investigated. This study show that the addition of nanocrystals alters the structure, the morphology, increases current efficiency and the corrosion resistance of the Zn-Ni coating and these effects are more significant with the addition of 2% v/v. The results obtained indicate that the addition of the CNC-Sif in the Zn-Ni coating is promising, because it reduces the energy consumed during the electrodeposition process in addition to increasing corrosion resistance of the Zn-Ni and the microhardness.

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Dynamic mechanical analysis (DMA) and drilling performance of the polypropylene (PP) composites reinforced with different volume fractions (0, 10, 20, 30, 40 and 50 vol.%) of untreated and alkali treated novel Alstonia macrophylla (AS) fiber were investigated. DMA reports showed that 40 vol.% fiber loaded PP composites imparted good thermomechanical properties in terms of storage modulus (E’), and loss modulus (E”) with a remarkable 366% and 331% improvement than virgin PP laminates respectively. In addition, study also disclosed that, alkali treated composites exhibited higher DMA properties than untreated PP composites owing to strong interfacial bonding of fiber and matrix as result of alkali treatment. Drilling study was also performed to investigate the effect of chemical treatment and drill parameters viz., drill point angle (90°, 118°, and 130°) and feed rate (20, 40, and 60 mm/min) on machinability property of PP/AS composites. Drilling outcomes conveyed that alkali treated PP/AS composites showed slight resistance to drilling than untreated composites owing to strong interfacial strength which played a vital role in resisting thrust force. Field emission scanning electron microscopy (FESEM) was used to capture the images of the drilled surface to understand the morphology of the PP/AS composite.

Resumo em Inglês:

Hydrogen permeation tests and tensile mechanical tests were performed at room temperature on API 5CT P110 steel to characterize hydrogen trapping and to evaluate their hydrogen embrittlement susceptibility. The hydrogen trap density was calculated from two consecutive hydrogen permeation transients plotted using an electrochemical cell. Slow strain rate tensile tests on hydrogen-charged samples through cathodic polarization at different potentials were performed to evaluate the hydrogen embrittlement susceptibility. Thereby it was established the lowest potential that characterizes the onset of the cathodic overprotection for studied steel. After mechanical tests was observed a decrease in ductility as the protection potential became more negative and that the fracture mode was changed from ductile microvoid coalescence on the as-received steel to extended quasi-cleavage on the hydrogen-charged steel. The results showed that API 5CT P110 steel has high susceptibility to hydrogen embrittlement conditioned by a predominance of reversible traps in microstructure and by high hydrogen solubility.

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The structural performance of metallic components is a significant challenge especially when it comes to operating conditions in real-world applications. Friction stir additive manufacturing (FSAM) is a solid-state additive manufacturing (AM) that provides controlled microstructure with homogenous grains and excellent structural performance. In this study, the FSAM technique was utilized to fabricate a lightweight laminated AA6061/AA7075 metal matrix composite with improved mechanical properties. The feasibility of the FSAM was demonstrated to build multi-functional, multi-material components for aerospace, automotive, and defence industries to enable lightweight, high-strength components. The FSAM tool was designed with an optimum shoulder length, shoulder diameter, pin length, and pin diameter considering the plate thickness. Afterward, optimized process parameters were designed using the Taguchi L9 orthogonal array (OA) technique. Microstructural features and their effect on mechanical properties such as microhardness and ultimate tensile strength (UTS) were evaluated in the FSAM build. FSAM build improved in microhardness (from 107±1.2 to 138.4 ±2.8 HV0.2) and tensile strength (from 310 to 384 MPa) as compared to base material AA6061. Corrosion resistance was also studied to understand the feasibility of the FSAM technique in various environmental conditions. The overall performance of the FSAM build shows promising results compared to the base materials.

Resumo em Inglês:

In the current research Al7075 (Al-5.4Zn-2.6Mg) alloy and composite prepared by dispersing 2 wt.% granite powder and 3 wt.% Si3N4 in Al7075 are subjected to peak aging treatment at 100, 120 and 1500C to obtain the maximum induced hardness by solid solution strengthening. In succession, by the results of peak aging treatment the alloy and composite are pre aged and heat treated by three step aging conditions. The results indicated that pre aged three step aging has resulted in enhanced alloy hardness of 185.6 VHN as compared to peak hardness of 142.9 at 1000C resulting in 29.88% improvement. Moreover, the composite subjected to pre-aged three step aging has resulted in improved hardness to 197.6 VHN as compared to peak hardness of 153.5 at 1000C resulting in 28.72% improvement. Also, the alloy and composite in this condition showed an improvement of 21.38% and 16.34% respectively in the UTS. Also, particularly composite displayed excellent wear characteristics as compared to as cast alloy. An interesting fact noticed in this work is that in three step aging the last step having higher temperature and longer duration of aging has resulted always a better hardness and hence has improved mechanical properties. This may be due to increased aging kinetics during heat treatment. The novel approach developed in this study will reduce the longer duration of conventional aging heat treatment and the energy consumption.

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This study aims to examine the potential improvement of uniform corrosion resistance and critical pitting potential of AISI 316L stainless steel (SS) in a simulated marine environment containing 3.5 wt. % NaCl by applying layer of gelatin containing HfO2 nanoparticles using spin coating. Also, to examine the statistical significance of using different weight fractions of HfO2 in the applied layer on the corrosion protection performance. The corrosion performance was assessed from potentiodynamic polarization. X-ray diffraction (XRD) was used to check the presence of HfO2 in gelatin matrix. Scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX) were used to examine the surface morphology and elemental composition of corrosion products. The results showed that the applied nanocomposite coatings enhanced both uniform and localized corrosion resistance of the underlying AISI 316L SS, also Analysis of Variance (ANOVA) test approved that the weight fractions of dispersed HfO2 nanoparticles have a statistical significant effect on the corrosion performance. Nanocomposites coating having 2 wt.% of HfO2 showed the best performance as compared to other examined coatings.

Resumo em Inglês:

In this study, scaffolds whose main phase is an icosahedral quasicrystal (i-QC) were prepared for the first time by dynamic freeze-casting. Two different metal powders were used here, namely pure aluminum and quasicrystalline particles from the Al-Cu-Fe system. These powers were initially mixed with deionized water, citric acid, and poly(vinyl alcohol). The obtained slurry was frozen while rotating and freeze-dried under vacuum. The green bodies were subsequently heat-treated in a reducing atmosphere. The total porosity and mean pore size evaluated for these scaffolds were 62.4 ± 3.0% and 67.3 ± 2.8 μm, respectively. This is the first time that dynamic freeze-drying has been used in the preparation of QC scaffolds, which reinforces the novelty of this study. In addition, the proposed route is simple, inexpensive, and environmentally friendly, which is also worth highlighting.

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Parameter optimization is an important step in the laser powder bed fusion (L-PBF), since process defects greatly impact the mechanical properties of the final parts, especially in components that undergo cyclic loading, such as molds and dies. The present study used the H13 tool steel to show that it is possible to perform a good parameter optimization quickly and with relatively few samples. The Box-Behnken experiment design model was used along with the application of the response surface methodology. Laser power, scan speed, and hatch spacing were used as independent variables, and density and porosity were chosen as the response. Power and speed most influenced the responses, but the interaction between power and speed, and power and hatch also had a significant influence. New optimized samples showed lowest porosity, confirming the effectiveness of the model. Density can be used during parameter optimization without impairing the optimization quality.

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In this work, composite powders of aluminum alloy 7075 (AA7075) reinforced by 2 weight percent of nanosized particles of silicon carbide (SiC), titanium nitride (TiN), and zinc oxide (ZnO) were produced in a bath of isopropyl alcohol by high energy ball milling during 480 min at 25 ºC, 900 rpm, and Balls-to-Powder Weight Ratio (BPR) of 20:1. The techniques of X-Ray Diffraction (XRD), Laser Diffraction Method (LDM), Scanning Electron Microscopy (SEM), and microanalysis of Energy Dispersive Spectroscopy (EDS) were used to characterize the powders as received and processed. Then, the composites were hot extruded and characterized by XRD, SEM, and microhardness Vickers (HV). The milling process reduces the crystallite and particle size to around 30 nm and 10 µm, respectively. After extrusion, a fine microstructure and good consolidation were found for all bars, except for AA7075 as received. The ranging microhardness values were from 97 HV to 121 HV.

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Herein, the applicability and performance of 22MnB5 steel sheets as protective masks over hot forging dies has been analyzed. Two masks were obtained following two different approaches; by heat treatment of flat sheets in cooling conditions similar to the process of hot stamping and hot stamping on the axial geometry of a cylindrical part. In both processes the sheets were austenitized at 1100° C for 7 min and to obtain bainite microstructure, they were maintained at temperatures higher than 700°C. The flat and axial masks have been subjected to 100 forging cycles for each geometry and positioned on the lower surface of hot forging dies. Surface integrity has been analyzed from microhardness profiles, roughness tests, thickness measurements, optical and electron microscopy. Wear mechanisms have been observed in both masks which was more expressive in the axial mask. Abrasive wear and plastic deformation have been actively observed in both masks; however, they have shown firmness for application as masks.

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Additive manufacturing using vat photopolymerization has gained attention for creating intricate ceramic parts. Digital light processing (DLP) is known for its high resolution and speed, but achieving stable ceramic suspensions with high solids concentration and low viscosity is challenging. This study investigated the impact of different dispersants on the rheology and stability of photopolymerizable suspensions. A commercially available water-washable resin, along with three dispersants (Castament FS 10, Triton-X, and DISPERBYK-111), and reactive alumina powder were used to formulate various ceramic suspensions. Viscosity and stability measurements determined the most efficient dispersant and concentration for DLP ceramic part production. Results showed that suspensions with DISPERBYK-111 had optimal viscosity and stability. However, the commercial resin presented higher viscosity, limiting solid loading to 40 vol.% alumina. Successful printing trials were conducted using a commercial printer. The alumina parts were thermally treated at 1550ºC, resulting in ceramics with a good surface finish, well-defined and adhered printed layers, 53.3% relative density, 19.65% XY shrinkage, and 13.69% Z-axis shrinkage.

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The research interest in developing alternative solutions to replace conventional synthetic fibers with natural fibers in composites is due to the several possible benefits of using these fibers, such as low cost, low density, high specific strength and high availability. The objective of this study was to produce hybrid composites from a commercial ortho-terephthalic unsaturated polyester resin obtained from the recycled PET (polyethylene terephthalate) glycolysis reinforced with sisal/glass fibers obtained by the vacuum infusion process. The composites were produced with 3 layers of fibers, the volume of each layer was fixed, and the amount of resin used was the same. For the results, the relative density decreased up to 23% and the moisture absorption reached up to 10.41%, being possible to observe the influence of the layer arrangement on the results. From the mechanical tests of tensile, flexural and impact strength it was observed that the properties decreased as sisal fibers were added, except in the results of maximum deflection in the flexural test of formulations. From the SEM (scanning electron microscope) analyses showed some defects in the direction of the thickness of all formulations produced, possibly from the process conditions adopted and the moisture present in the sisal fibers, which negatively affected the results of mechanical properties and moisture absorption. According to the results of this study, it was possible to obtain some proposed formulations of hybrid composites, such as the (F1), composed of glass, sisal and glass layers (|GSG), which reached properties close or equivalent to those of the reference composite (F0), composed of glass, glass and glass layers (|GGG) and which showed to be potential alternatives to replace conventional glass fiber composites.

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This work presents a detailed study directed to supermartensitic stainless steels (SMSS) alloyed to nitrogen (UNS S41425) and vanadium (UNS S41427), showing comparison between them by varying their tempering temperature, evaluating the behavior in its mechanical properties, presenting a fractographic and microstructural analysis between these alloys, besides to demonstrate techniques for modeling these strain-hardening results with best coefficients that determine these materials with good predicted values. The Hollomon, Voce and Chaboche models were determined, using an iterative regression method (R2) in order to obtain the best coefficients for each analysis condition. This work concludes by presenting graphic results of the effect of tempering temperature increase on the final mechanical properties, evaluates the differences obtained between these materials and presents an evaluation of the behavior of each coefficient of the models presented separately, showing the best R2 fitting results. With the models determined, it is possible to use the results in this work to perform numerical simulations and meet the needs of the engineering on industry.

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Rigid polyurethane foam (PUr) is a common residue from the footwear industry that seeks a sustainable disposal alternative. A flexible composite incorporating PUr that could be used in this same industry is an exciting solution. Poly (vinyl chloride) (PVC) and polyvinyl butyral (PVB) were tested as possible matrixes for flexible composites containing 20%, 35%, and 50% of PUr produced by two different processes, extrusion and injection molding. PVB/PUr and PVC/PUr were compared considering the morphology observed with scanning electron microscopy (SEM), density, degradation during processing, and dynamical mechanical properties. PVC was severely degraded when processed with PUr and showed a low adhesion to PUr particles resulting in decreased storage modules and increased glass transition temperature. PVB is a better matrix for PUr flexible composites since it showed no sign of degradation and formed a stronger interface with PUr particles resulting in PVB/PUr composites with higher storage modulus.

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Vanadis®8 is a high-value tool steel, that undergoes gas atomization and hot isostatic pressing during production , resulting in costly waste. Repurposing this waste material through powder metallurgy (PM) offers a cost-effective solution. This study explores the PM process applied to Vanadis®8 steel scraps, involving high energy ball milling, uniaxial pressing, and sintering. The final product and the as-received steel underwent heat treatments, including quenching and tempering. Microstructural evaluation employed X-ray diffraction and scanning electron microscopy, while physical evaluation entailed Archimedes density measurements. Mechanical analysis was carried out through microhardness and compression strength tests. Results revealed that optimal milling conditions were achieved at 30 hours with 400 rpm (s-1). Vanadis®8 steel produced through PM attained 85% densification compared to the as-received material (6.31 g/cm3). MC-type carbides were present in all evaluated conditions. Heat treatments improved mechanical values for all conditions, suggesting that PM-produced Vanadis®8 steel, subjected to quenching and tempering, presents a viable reuse option.

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With increasing life expectancy, revision surgeries have become more frequent in implanted people. This is due to the biological and biomechanical incompatibility that generates, among others, problems such as stress shielding. This works aims to analyze the influence of the hot rolling process (HR sample) on the microstructure and, consequently, the properties of β-Ti multiprincipal alloys: Ti-27Nb-39Zr (39Zr), Ti-30Nb-50Zr (50Zr), and Ti-20Nb-30Zr-13Ta (30Zr) (wt. %.) (equimassic and with high content of β-stabilizer elements). All samples were subjected to characterization through X-ray diffraction (XRD) to determine the phases present, and optical microscopy (OM) and scanning electronic microscopy (SEM) were realized to characterize the microstructure and confirm the phases obtained through XRD. Before hot rolling, only the β phase was identified, but in the HR condition, the α and β phases were identified. Consequently, it did not observe significant changes in microhardness for all alloys, while the elastic modulus was observed with a reduction of 23% for 39Zr, 46% for 40Zr, and 13% for 30Zr. The hot rolling processing was confirmed to be a helpful route to reduce the elastic modulus for β Ti multiprincipal alloys opening perspectives for applying such alloys as metallic implant materials.

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We investigate the structural, optical, thermal-optical, and electronic properties of TiNx thin films utilizing a variety of experimental techniques, including spectroscopic ellipsometry, Raman spectroscopy, scanning electron microscopy, atomic force microscopy, thermal lens spectroscopy, and UV-VIS spectroscopy. Our experimental results indicate a remarkable metallic character in the TiNx thin films deposited under lower N2 flow during treatment, as well as an increase in reflectance in the infrared region and thermal diffusivity as the partial N2 flow is reduced, which is consistent with previous experimental studies. The microscopic origin of these trends is explained in terms of the atomic structure of the system, where Ti atoms contribute free carriers that interact with IR radiation and N atoms create imperfections in the lattice, causing greater scattering of phonons, respectively. The experimental results also indicate that the roughness of the films produced with a lower N2 partial flow was lower than that of the films with a higher N2 partial flow. To explain the deviation of optical properties from the ideal case, surface oxidation is also investigated. This facilitates the coating of smarting windows with TiNx thin films.

Resumo em Inglês:

Zr-Si-N thin films were co-deposited by reactive magnetron sputtering to verify the influence of silicon content (1.6 and 8.0 at. % Si) and substrate temperature (room temperature and heated to 973 K) on structure, morphology, chemical bonds and hardness. GAXRD shows a change in grain orientation from (111) to (200) due substrate heating for sample Zr0.984Si0.016N, furthermore, it was not possible to identify any silicon compounds in all deposited samples. SEM-FEG images show greater roughness and surface clusters for sample Zr0.920Si0.080N due to the heat applied on the substrate, with Si3N4 decomposition, influencing thin film hardness. XPS analyses of Si 2p photoelectronic region shows only Si3N4 presence in all samples, proving, in conjunction with other characterization results, the non-formation of substitutional or interstitial solid solution, regardless of substrate heating or silicon content added to ZrN matrix.

Resumo em Inglês:

In this work, mixtures of ceramic powders containing Al2O3 with different amounts of Y2O3 (1%, 3%, 5% and 10wt.%) along their cross-section were fabricated to obtain multilayer composites based on Al2O3 with different levels of Y3Al5O12 (YAG) as reinforcement. Monolithic cylindrical multilayer Al2O3 blocks were compacted and subsequentially, sintered at 1610°C for 4h. Phase stability, microstructural aspects, and physical and mechanical properties of the specimens were acquired by relative density, X-ray diffraction, scanning electron microscopy, Vickers hardness, fracture toughness, Young’s modulus and biaxial flexural strength measurements. The results indicated that monolithic alumina specimens exhibited relative density of 98%, with average hardness of 1203 ±83 HV, fracture toughness of 2.1 ±0.8 MPa.m1/2 and flexural strength of 187 ±64 MPa. Progressive incorporation of Y2O3 into the chemical composition of the specimens led to formation of the YAG phase by solid state reaction during sintering, which reduced hardness and increased densification, fracture toughness and flexural strength, with average values of HV=1023 ±28 HV, KIC=3.5 ±0.3 MPa.m1/2, σf=273 ±58 MPa and 14% Y3Al5O12 for the specimens with 10wt.% Y2O3. This improvement is probably associated with toughness mechanisms, such as crack deflection and residual thermal stresses between the phases present in the composites.

Resumo em Inglês:

The present study reflects on the wear behaviour characteristics of A356 composite with trace addition of copper and copper-coated zinc as reinforcements. Dry sliding wear tests were conducted on fabricated as-cast and heat treated composites by varying load of 20-60 N under constant sliding speed of 1 m/s and sliding distance of 3000 m. Results confirmed that copper-coated zinc was successfully introduced as reinforcement into A356 matrix using two-step casting method. Scanning Electron Microscope (SEM) images confirmed the presence and homogeneous distribution of the added reinforcements in the matrix. T6 treatment with addition of Cu reinforcement facilitated age hardening showing 121% hardness improvement compared to as-cast matrix A356. At lower loads, wear results showed 117-134% enhanced wear resistance in composite reinforced with 1 wt.% Cu and aging at 100°C. However at higher loads, 153-210% improvement in wear resistance was observed. Overall, copper and Cu-coated zinc reinforced composite along with T6 treatment exhibited significant improvement in hardness wear property compared to as-cast matrix A356 alloy.

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In this paper, the oxidation behavior of silicon nitride with different contents of TiN was evaluated at 1400 oC for 64 hours in air. The oxidized samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. Weight gain measurements have shown that the oxidation followed a multiple-law model with linear, parabolic, and logarithmic contributions. The samples presented high weight gain at the beginning of the process followed by the formation of an amorphous silica surface layer containing Y2Ti2O7 and rutile crystals. Cracks and holes were detected on the oxide layer. The oxidation resistance of the composites was strongly influenced by the initial content of TiN.

Resumo em Inglês:

Biomedical engineering has been constantly looking for the development of new materials that have bioactive surfaces and that are responsible for new bone formation, induce osteoblast differentiation and present antibacterial properties. Here, we present innovative and applied research to evaluate the influence of niobium pentoxide thin films (Nb2O5) deposited on the surface of a Ti-6Al-4V alloy via the reactive sputtering technique on antibacterial activity, on the cellular proliferation of MC3T3 cells and on biomineralization capacity. Results demonstrated the reactive sputtering technique improved the cell viability, the osteogenic performance of cells involved in the osseointegration process, the ability to delay bacterial proliferation within the first six hours of contact with S. aureus as well as the capacity to promote rapid amorphous apatite formation in vitro. These findings confirm the great potential of the Ti-6Al-4V alloy functionalized with Nb2O5 for future applications in implantable devices.

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Shape memory alloys (SMA) are now widely studied in academia and have increasing usage in industry, as they allow efficient performance compared to mechanic actuators with reduced dimensions and the possibility of sensing temperature through the material itself. A subclass of the SMAs are the alloys with magnetic shape memory, still little explored as intelligent materials in Brazil. They combine the best properties of SMAs and common magnetostrictive materials. The magnetic shape memory alloys (MSMA) can be activated not only by the presence of a thermal stimulus, but also by the presence of an applied magnetic field. In this research, the polycrystalline magnetic shape memory alloys Ni51.3Mn24Ga24.7 and Ni54Mn21Ga25 were manufactured and characterized. Differential scanning calorimetry, X-Ray diffraction, energy dispersive X-ray spectrometry and scanning electron microscopy analyzes were performed to thermoanalytically and crystallographically characterize the alloys. Magnetic characterizations were also performed using Magnetic force microscopy. The results of the characterizations showed that the production process and the heat treatment were satisfactory for the fabrication of the ferromagnetic polycrystalline alloys. Besides that, the compositions Ni51.3Mn24Ga24.7 and Ni54Mn21Ga25, presented austenitic and martensitic 5M structures, respectively, at room temperature and it was possible to observe the alignment of the magnetic domains after magnetization.

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Poly(methyl methacrylate) (PMMA) is a polymer with applications in the medical and aerospace industries that require resistance to gamma radiation. However, the effects caused by gamma radiation on PMMA properties may make its application in situations of exposure to gamma radiation unfeasible. In this study, the impact of commercial additives on the radiolytic stabilization of PMMA will be studied through viscosimetric assays. In a preliminary trial, additives with different mechanisms of action were tested, and the efficacy of two additives (Tinuvin 770 and Tinuvin 622) hindered amine stabilizers (HAS) types were registered. PMMA films with the additives at different concentrations were exposed to gamma radiation and studied through viscosimetric molar mass and G-value. The Tinuvin 622 at 0.3 wt% showed the best performance in the radiolytic stabilization of p PMMA films at the 20-50 kGy range. Antagonism was observed when Tinuvin 700 and Tinuvin 622 mixture was studied in different proportions. These results show the potential of commercial additives, initially produced for other purposes, in the radiolytic stabilization of PMMA.

Resumo em Inglês:

The mechanical Properties of an experimental 17%Cr multiphase alloy were studied as function of heat treatment parameters. Containing majoritary ferrite and martensite, this type of steel is applied in tubullars and casings in the off shore oil and gas production, where high corrosion and mechanical resistance are required. Quenching and tempering heat treatments produced different combinations of ferrite, martensite, austenite and precipitates. The as quenched material has 35% of ferrite, martensite and 3.8% of retained austenite. The material quenched and tempered at 500oC has lower austenite (1.2%), and tempered martensite with Nb carbides. The tensile properties were excellent, but the low temperature (-46oC) impact toughness was very small. A high toughness was obtained in the material quenched and tempered at 650oC, with a microstructure of ferrite, tempered martensite and 7.2% of reversed austenite, but the mechanical resistance was under 621 Mpa (90ksi), which is considered too low for the application envisioned. The material tempered at 600oC showed an interesting combination of mechanical resistance and low temperature toughness. The flow stress curves of the material were modelled by Hollomon’s equation and Voce’s equation with correlation coefficients (R2) higher than 0.98.

Resumo em Inglês:

A factorial design was used to evaluate the effects of processing variables on the morphology and microstructural characteristics of titanium dioxide (TiO2) fibers produced by solution blow spinning (SBS). For this, tests were carried out varying TiO2 precursor content, feed rate, air pressure, polymer, and solvent. The TTIP concentration and feed rate statistically influenced the average diameters of the PVC/TiO2 system. The proper combination between polymer and solvent enables the obtaining of TiO2 nanofibers with similar morphologies either using hydrophilic or hydrophobic polymer, however, fiber diameter is influenced by type of system (polymer/solvent) used. Only the anatase crystalline phase was found in the fibers with the PVC polymer and THF solvent, while two crystalline phases were obtained in the fibers with PVP and alcohol, anatase and rutile, indicating that the variation of the polymer and solvent influences the crystalline phases of the TiO2 fibers studied.

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In present work, erbium-doped PZT 52/48 ceramics at sites A and B were prepared by the Pechini method in order to study their dielectric properties. The aim was investigated the dielectric anomalies of interfacial origin in these ferroelectrics. The ceramics were also submitted to electrical measurement analysis. The dielectric response of the grains showed characteristics of materials that follow Curie-Weiss law which is typical of ferroelectrics. In high temperatures and low frequencies, it was detected the dielectric anomaly phenomenon for the ceramic samples. Impedance spectroscopy analyzes through equivalent circuit (brick-layer model), grain and grain boundary in series, exposed a predominance of dielectric properties of intergranular interfaces as the cause of this anomaly. The electrical characterization showed a peculiar ferroelectric-paraelectric phase transition around 390 °C for both samples.

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Nano-surface layers were prepared on the surface of 6061 aluminum alloy using the ultrasonic surface rolling process (USRP). The surface morphology, surface roughness, microstructure, hardness, and corrosion resistance of 6061 aluminum alloy were systematically characterized using X-ray diffraction (XRD), laser scanning confocal microscopy (LSCM), optical microscope(OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and other testing methods. The results showed that ultrasonic surface rolling strengthening did not change the surface phase composition of 6061 aluminum alloy. It changed the size of the surface phases and the distance between the phases while refining the surface grains. The static pressures has a great influence on the surface properties of 6061 aluminum alloy. The best surface properties were obtained under 500N static pressures. The surface hardness reached 129.5HV0.5, the surface morphology was flat and continuous, the surface roughness was reduced to Ra0.191μm, and the corrosion resistance was significantly improved.

Resumo em Inglês:

The effect of heat treatment on hydrogen diffusion and trapping on the API 5CT P110 steel was investigated trough electrochemical permeation tests and microstructural analysis techniques. Samples of as-received steel were tempered at different temperatures to obtain hydrogen permeation and trapping parameters and to characterize microstructural modifications that may alter these parameters. After permeation tests on each heat-treatment condition were verified changes on hydrogen kinetic parameters. Microstructural analysis revelated changes in dislocations density and volumetric fraction of titanium carbides, responsible to alterations in diffusivity, solubility and in hydrogen trapping characteristics. As these carbides are considered irreversible hydrogen traps, are beneficial because they become the steels less susceptible to hydrogen embrittlement. Therefore, the results suggest that there is an optimal tempering temperature which can make the API 5CT P110 steel more resistant against hydrogen embrittlement, since promote the formation of a higher number of irreversible hydrogen traps.

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The present work investigates the aquatic biodegradation of poly(3-hydroxybutyrate) (PHB)/nanoclay bionanocomposites containing PP-g-MA as compatibilizing agent. Both pristine and organically modified (Cloisite20A®) montmorillonite clay were used as fillers in different content (1 and 3 wt%). The bionanocomposites were prepared by melt intercalation in a single screw extruder. There after films (50x50x0.5mm) were prepared by compression and assessed by X-ray diffraction. Aquatic biodegradation of the films was appraised by visual inspection, optical microscopy, counting and identification of bacteria. Results proposed that the water of the Parnaíba River in the city of Teresina (Piauí, Brazil) has microorganisms (Pseudomonas putida and Pseudomonas aeruginosa) capable of degrading these bionanocomposite films, particularly the films with 3 wt% organoclay. Our data indicated the bacteria Pseudomonas aeruginosa degraded dexterously all the films. This work collaborates with the preservation of the environment and expands the use of bionanocomposites in expendable items with the development of films with properties favorable to biodegradation in aquatic environments. It is believed that PHB/clay/PP-g-MA films emerge as a promising alternative for the packaging industry.

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In this study, aluminum alloy 7075 (AA7075) nanopowders were prepared by High-Energy Ball Milling (HEBM) in a bath of isopropyl alcohol. The process was investigated in different milling times and silicon carbides (SiC) reinforcement percentual. The effects of these parameters on the samples were characterized by X-ray diffraction (XRD), Laser Diffraction (LD), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS). The XRD analyses showed that as the grinding time increases, the micro deformation also increases, while the crystallite and particle size decrease until a constant value at 480 min. If the percentual of SiC reinforcement increases until 5 percent, there is a minimum change in the results compared to AA 7075 milling 480 min with no reinforcement. On the other hand, when the AA7075 was milled for 480 min and reinforced by 10 percent SiC, the best structural refinement result was achieved.

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This work reports the study of the compatibilization of the blend of biopolyethylene and biopolyamide 6.10, both biobased. In this work, two polymers functionalized with maleic anhydride (PE-g-MA and SEBS-g-MA) were used as compatibilizers of the blend. The blends were prepared in a single screw extruder and subsequently molded by injection. SEM results showed the immiscibility of the Bio-HDPE/PA6.10 blend. With the addition of the compatibilizers, a compatible interface was formed. The DSC results showed changes in the crystallization behavior of the two phases with the addition of compatibilizers. FTIR results suggested that there was a reaction between the maleic anhydride of the compatibilizers and the terminal amino groups of the polyamide. The blend containing PE-g-MA showed greater stiffness, with an increase in the modulus of elasticity in relation to Bio-HDPE, while the blends containing SEBS-g-MA showed excellent resistance to impact and high elongation at break.

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This study seeks to synthesize, by the sol-gel method, an organic-inorganic hybrid coating of polyurethane, siloxane and silver nanoparticles to cover titanium prostheses, aiming to act as an anticorrosive protection barrier, inhibiting the release of metallic ions in the human body. In this context, a hybrid based on the TEOS (tetraethyl orthosilicate) alkoxide precursor was used to carry out the acid hydrolysis/condensation process. Then, silver nanoparticles were added, and the mixture was done with the incorporation of polycaprolactone diol, followed by the addition of hexamethylene diisocyanate, to form polyurethane. The hybrid coatings were applied on titanium plates, and morphological, physical-chemical and electrochemical characterizations were carried out, as well as the evaluation of bactericidal and antifungal activity, in order to evaluate the performance of the coatings and the influence of diferente concentrations of silver nanoparticles (10 mL, 20 mL and 40 mL). The results showed that although Híbrido 10 (lowest concentration of silver nanoparticles, 10 mL) presented the best morphological characteristic without cracks and with satisfactory roughness to obtain the best bacterial behavior, the Híbrido 20 sample presented the best electrochemical performance.

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High Chromium Cast Iron (HCCI) has demonstrated its effectiveness as a potential material for applications in severe environments due to its remarkable wear resistance attributed to the volumetric fraction of carbides in the microstructure. This study investigates a novel high-alloyed composition of white cast iron named High Entropy White Cast Iron (HEWCI), which merges the concepts of HCCI and high entropy alloys. Specifically designed chemical compositions incorporating Vanadium (V), Molybdenum (Mo), and Nickel (Ni) were employed to enhance its wear resistance properties. The solidification path, microstructural characterization, and wear responses of HEWCI were evaluated. XRD and SEM techniques were carried out for characterization purposes. Linearly reciprocating ball-on-flat sliding wear tests were conducted using a high-frequency reciprocation rig (HFRR) tribometer, assessing wear volume, linear wear rate, specific wear rate (κ), and coefficient of friction (COF). The results revealed microstructural refinement and precipitation of new carbides through V, Ni, and Mo additions. This approach demonstrates that adding carbide-forming elements and refining the microstructure are promising strategies for enhancing wear performance in HEWCI alloys.

Resumo em Inglês:

Nickel-based alloys containing high amount of Cr are desirable materials for the production of critical components that operate under high temperature and severe corrosion conditions. The description of flow behaviors for these alloys is key to designing the hot formation process for achieving the excellent mechanical properties of components. This work aims to study the flow behaviors of Ni-38Cr-3.8Al alloy during thermal deformation. A series of isothermal compression experiments were carried out at temperatures of 1148 K, 1223 K, 1298 K, 1373 K, 1448 K and 1523 K, and strain rates of 0.01 s-1, 0.1 s-1, 1 s-1 and 10 s-1. Results show that the obtained true stress-strain curves exhibit the softening characteristics of dynamic recrystallization (DRX) and dynamic recovery (DRV). The flow stress decreases with temperature increasing and strain rate decreasing. To further quantitatively describe the flow behaviors, an improved segmented Arrhenius constitutive equation was developed according to the softening characteristics under different temperatures. In these equations, the variable coefficients, including activation energy Q and material constants (structure factor A, stress exponent n, stress parameters α), were fitted as the polynomial functions of true strain. Furthermore, a typical Arrhenius constitutive equation was also solved. The comparisons between experimental stress and predicted results obtained from the typical and improved constitutive equations were conducted, and the correlation coefficient (R) and average absolute relative error (AARE) were calculated as 0.932, 15.83%, and 0.9963, 5.61%, respectively. It suggests that the improved constitutive equation can adeptly describe the flow behaviors of Ni-38Cr-3.8Al alloy.

Resumo em Inglês:

The aim of this investigation was to study and evaluate the fracture toughness (KICV) of an AISI M3:2 high speed steel that was prepared by powder metallurgical processing, which consisted of uniaxial cold compaction of irregularly shaped water atomized powders, without and with 0.3% of carbon in the form of graphite, followed by vacuum sintering to obtain compacts with densities close to its theoretical value. The sintered steels were then hardened by austenitizing, quenching and triple tempering. Chevron fracture toughness test samples were prepared from the compacts and the tests conducted to determine KICV. The microstructures of the specimens were examined by scanning electron microscopy (SEM), and the composition of the phases determined by x-ray diffraction analysis (XRD). The sizes of the primary carbides and of the austenite grains were determined using Quantikov digital analysis software. No significant difference in fracture toughness (KICV) between the two high speed steels AISI M3:2, austenitized at the different temperatures, was observed.

Resumo em Inglês:

The welding of metallic materials by the Friction Stir Welding (FSW) method is a very attractive process for preserving their characteristics, especially for copper and its alloys that require high heat input and present many distortions by traditional methods. However, it is a great challenge to produce welds free of defects and maintain or improve their mechanical properties. In the current literature data on FSW parameters for copper and its alloys are scarce. In this study, tests were performed with a combination of four tool rotations (750, 850, 950, 1050 rev.min-1) and two welding speeds (20 and 60 mm.min-1), maintaining the tool inclination angle in 3° and waiting time of 5 seconds. The objective of this work is to analyze the microstructure and mechanical performance of lap joints of the UNS C19400 alloy joined by FSW. The process temperature was monitored to trace the heating profile of the process, in addition to microhardness and shear strength tests, in addition to optical microscopy for analysis. The joints welded by the parameters Ω 950 rev.mm-1 𝛖 20mm.min-1 obtained a mechanical performance of 73% compared to the characteristics of the base metal and despite the appearance of volumetric defects at the microstructural level, the metallurgical transformations of recovery and recrystallization of the grains observed in the microstructure played a key role in the result.

Resumo em Inglês:

A direct-doping method was tested to design new composite-glasses by incorporating lanthanum niobate nanocrystals (NC) in tellurite glasses. NC powder were grinding with glass powder before heating-quenching, with the main investigation approached of best parameters for NC suitable homogenization but limited dissolution. Thermal analysis signalizes that prior heat-treatment of NC promotes higher transparency and limits NC dissolution. These materials with visually detectable NC aggregates exhibited glass transition temperatures close to the starting glass. LaNbO4 phase was hardly detected by X-ray diffraction because of the low weight ratio and partial dissolution but the monoclinic polymorph could be identified for lower time. UV-visible-NIR transmission spectra also related progressive lower transparency with light scattering of NC aggregates. Photoluminescence suggest that lower times allowed to ensure the NC environment with lower crystallinity around Eu3+-ions in final composite-glass. These results pave the way for designing new materials containing NC not achievable by conventional nucleation-growth methods.