Resumo em Inglês:

Abstract High Chromium Cast Iron (HCCI) is mostly utilised in environments under severe abrasion and corrosion wear conditions, and research on this material with added niobium obtained positive results regarding wear resistance. The casting process has surface finish and dimensional accuracy limitations compared to machining processes. There are too few studies about HCCI machinability and no one about HCCI with niobium additions. HCCI machinability studies may allow new applications for this material when excellent surface finish and high dimensional accuracy are required. This study analyses the influence of 0.5% Nb addition on the microstructure and machinability of a HCCI alloy with 25.6% Cr and 3.2% C. The samples were heat treated and subsequently machined in dry cutting conditions. Annealing was used to facilitate the pre-machining of the samples, which were later quenched and tempered. Microstructure and hardness were analysed at each stage of the heat treatment. The material was machined after tempered using polycrystalline cubic boron nitride (pcBN) tools. The alloys solidified in the hypereutectic condition. The addition of niobium reduced the hardness and carbide volumetric fraction, increased the service life of the cutting tools in all tests, provided better surface finishing and modified the wear mechanisms.

Resumo em Inglês:

Abstract In the present work, the warm roll bonding (WRB) technique was adopted to fabricate 3 layers of Aluminum-perforated Copper 260-Aluminum (AL/perforated CU/AL), and five layers of (AL/Polyurethane (PU)/perforated CU/PU/AL) sandwich composites. Two different tests were adopted, namely peel test and small punch test (SPT), to study the peel strength and flexural behavior of these sandwich composites, respectively. The main manufacturing parameters, including interface properties, rolling speed, and the number of passes, which control the strength and integrity of these sandwich composites were studied experimentally. Furthermore, the three-dimensional finite element method was carried out to study the effect of the presence of pre-crack on the peeling test and SPT specimens numerically. The present results indicated that the peeling resistance is mainly dependent on the roughness of the interface and elapsed time in manufacturing processes. The flexural behavior of sandwich composites measured from SPT agrees with the first principles of mechanics of materials, i.e. there is a marginal effect of the bond strength between the layers.

Resumo em Inglês:

Abstract In Brazil, the production of each ton of steel generates approximately 621 kg of waste and direct co-products. One of the components that generates a high amount of waste is the refractory material used in the steel process. So, in this study, the possibility of using MgO-C refractory waste from steel casting pots after their deterioration for the formation of chemically bonded phosphate ceramics was investigated. This work aims to study the recovery of industrial solid waste from MgO-C refractories by determining the processing conditions necessary to obtain magnesium phosphate ceramics. Three mean particle size of the waste and three potassium monophosphate:MgO ratio in the mixture were adopted. All mixtures showed the formation of the K-struvite phase and a strong relationship between the compressive strength and porosity properties. The highest compressive strength value obtained, 7.51 ± 0.24 MPa, is sufficient for use in several areas of engineering. It was also possible to statistically represent, using a quadratic model, the variation in porosity in relation to the phosphate content and particle size of the waste, obtaining porosities ranging from 14% to 25%. Taking into account this study used a waste, the evaluation of its environmental impact assumed an important role. The waste showed no appreciable toxicity, while some samples W3-20 showed toxicity to Allium cepa L. and Artemia salina. Considering the presented properties, the obtained material could be used as a structural block, filters, support for catalysts, and repair element for cement-based structures and roadways.

Resumo em Inglês:

The first stage of the solidification of metal alloys is nucleation, during this stage is defined the number of grains present in the final structure, just as the conditions in which the same will grow. The application of pressure in the solidification is mostly studied as an operational parameter, and its effects are described and commented extensively in literature. The objective of this paper is to study the effect of pressure on nucleation, still not to describe but to explain it, for this purpose the pressure is treated as a thermodynamic variable. From this analysis it was possible to determine the real influence of pressure on the activation energy, being clear that its effect is equivalent and co-dependent to that of the undercooling, and can thus cause considerable variations in the activation energy, much larger than what is proposed in previously published papers that approach the subject, causing a considerable stimulus on nucleation. It was also observed that the curve that represents the effect of pressure on the activation energy proposed in this paper, has a similar form to the curves that describe how the pressure refines structures, resulting from the process of solidification under pressure reported in literature.

Resumo em Inglês:

Abstract Bacterial colonization plays a key role on the pathogenesis of peri-implantitis and may be influenced by titanium surface topography. The aim of this in vitro study was to evaluate the influence of titanium topography after fluoride ions deposition in the bacterial colonization. Machined (M), double acid-etched (DE) and double acid-etched surface with fluoride ions deposition (Nano F-) were analyzed by scanning electron microscopy, contact angle and roughness (Ra). Streptococcus mutans viability was quantified by Live/Dead Baclight bacterial viability kit. The mean Ra/contact angle values were 0.20 μm/69.13°, 0.53 μm /92.82° and 0.56 μm/94.33° for M, DE and Nano F-, respectively. M surface presented significantly lower live bacterial counts when compared to the Nano F- surface (p=0.007). The dead bacteria count was higher on the Nano F- surface (p=0.001) than on the M and DE surfaces. Crystalline deposition of fluoride ions (Nano F-) promoted an increase in dead bacteria on the tested titanium surface.

Resumo em Inglês:

Abstract Recently, Dai et al. published a paper in Research Materials 2019; 22(5): e20190311. They have investigated the visible-light photocatalytic activity of the synthesized Bi2WO6 powders1. In the context of determining of band gap energy based on diffuse reflectance measurements, the cited authors make some mistakes, which are clarified in the present letter.

Resumo em Inglês:

Abstract Titanium and its alloys are widely used as implant materials and many studies to accelerate the osseointegration have been performed. This work aims to evaluate the formation of a bioactive surface in commercially pure titanium (cp-Ti) grade 4 after alkali (AT) and heat treatments at 600 °C (AHT600) and 900 °C (AHT900). Characterization techniques were SEM, AFM, Raman, TF-XRD, wettability, nanoindentation and indentation adhesion. Additionally, SBF soaking tests were performed to evaluate apatite growth and showed that alkali and heat treatment accelerates apatite growth. The AT samples formed sodium hydrogen titanate (1 µm thick), and AHT600 and AHT900 formed sodium titanate (1 µm thick), while rutile TiO2 increased with temperature, reaching up to 5 µm thick and the surface changed from slightly hydrophilic to fully hydrophilic. Roughness and surface area increased, especially in AHT900. The hardness of the surface layer was significantly increased by the heat treatment.

Resumo em Inglês:

Abstract This paper presents the characterization of austenite to pearlite transformation in rail steels (premium and standard) using dilatometry. The critical transformation temperatures were measured as a cooling rate function and the obtained microstructures were qualitatively and quantitatively characterized. Aiming to study the transformation kinetics, three equations proposed by technical literature were evaluated in order to predict the transformation evolution. Experimental and calculated CCT diagrams were compared. It was concluded once the kinetics of phase transformation in rail steels is well characterized, it can be used as reference to enable suitable heat treatment to obtain pearlitic microstructures for the standard steel as refined as those of premium. The minor prior austenite grain size of the standard steel favoured the pearlite nucleation, however its highest Mn, Nb and Si contents delayed the growth stage. All equations evaluated in order to predict the kinetics of austenite to pearlite transformation under continuous cooling were satisfactory.

Resumo em Inglês:

Abstract An electrochemical sensor based on a modified glassy carbon electrode (GCE) with reduced graphene oxide and Ni-Au nanoparticles (Ni(OH)2/AuNp/rGO/GCE) was developed for the determination of ethylene glycol. The graphene oxide was reduced electrochemically at the electrode surface by chronoamperometry, the gold nanoparticles were deposited by chronopotentiometry while the nickel hydroxide nanoparticles were deposited by cyclic voltammetry. The characterization of graphene oxide was performed by Raman spectroscopy, X-ray diffraction (XRD) and transmission-mode scanning electron microscopy (TSEM), while the modified electrodes were characterized by scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) analysis. The determination of ethylene glycol was performed by cyclic voltammetry due to the regeneration of the active sites, preventing loss of the sensor signal. The modified GCE with rGO and Ni(OH)2/AuNp showed a good performance obtaining a linear range of 0.24 to 1.4 mmol L-1 with a correlation coefficient of 0.9903, limits of detection and quantification (49 and 162 µmol L-1, respectively) and high stability with 500 continuous analysis cycles.

Resumo em Inglês:

Abstract Herein, metal-oxide-semiconductor fields effect transistors (MOSFET) are fabricated and characterized. p− type germanium dioxide coated onto Au/n-CdSe substrates and top contacted with carbon point contacts is used to form the MOSFET devices. The structural investigations which were carried out with the help of X-ray diffraction technique revealed large lattice mismatched polycrystalline layers of CdSe and GeO2. The design of the energy band diagram has shown the formation of two Schottky arms (Au/n− CdSe, C/GeO2) at the interfaces of the n− CdSe/p− GeO2 layers. The capacitance-voltage characteristics which are recorded in the frequency domain of 1.0-50.0 MHz revealed the ability of formation of NMOS and PMOS layers. The signal frequency controlled built in potential is tunable in the range of 2.34 and 5.18 eV. In addition, the conductance and capacitance spectral analyses in the frequency domain of 10-1800 MHz revealed the domination of current conduction by tunneling and correlated barriers hoping below and above 760 MHz, respectively. In addition to its features as MOSFET devices, the Au/CdSe/GeO2/C hybrid devices are found to be appropriate for use as microwave cavities.

Resumo em Inglês:

Abstract In this work, surface mechanical attrition treatment (SMAT) was employed to rejuvenate ZrCuAlNi bulk metallic glass (BMG) plate. Differential scanning calorimetry (DSC), atomic force microscopy (AFM) and nanoindentation analyses were carried out to evaluate stored energy and micro-mechanical properties of treated BMGs. According to DSC results, 10 min SMAT process increased the stored energy of BMG plates up to 50%. AFM analysis showed that the structural rejuvenation occurred in the bulk of samples and just a slight rejuvenation gradient was detected from the front to the back side of BMG plates. Nanoindentation analysis indicated that the structural rejuvenation is consistent with anelastic strain induced under the SMAT process. It was also found that an optimum treatment time is needed for maximum rejuvenation in the BMGs. This event is due to the fact that the glassy structure is able to store a critical anelastic strain, which leads to a saturated condition in rejuvenation.

Resumo em Inglês:

Abstract Supermartensitic steels represent a new sub-class of martensitic stainless steels with higher toughness and corrosion resistance than conventional grades. These properties were improved by the drastic reduction of carbon content, and the addition of nickel and molybdenum. These chemical composition changes also increased the weldability of these steels, since the soft and ductile martensite formed is not susceptible to cold cracking during welding. However, post weld heat treatment may be necessary for uses in sour, aggressive and embrittlement environments. This work investigates the mechanical properties of a weld produced by gas tungsten arc welding (GTAW) of a pipe of 12%Cr supermartensitic stainless steel with 625 nickel alloy as filler metal. The response of the weld metal to post weld heat treatments at 650oC was also evaluated.

Resumo em Inglês:

Abstract The synthesis of SSZ-13 was studied by evaluating the influence of two types of crystallization seeds with CHA structure (S1 seeds prepared in fluoride medium and S2 seeds by the conversion of zeolite Y), SiO2/Al2O3 (28, 40, 60 and 100) and OH/SiO2 (0.6 and 0.8) ratios. Choline chloride was used as the structure-directing agent and the crystallizations occurred at 140 ºC from 24 to 96 h. S1 seeds led to the coexistence of zeolites SSZ-13 and P, while S2 seeds promoted in all SiO2/Al2O3 ratios and OH/SiO2 = 0.8, the formation of pure SSZ-13 after 24 h. The SSZ-13 samples are formed by clusters of crystals with cuboid-like morphology and exhibited textural properties typical of CHA framework. SSZ-13 zeolite led to a decrease in the temperature and the activation energy required for the degradation of ultra-high molecular weight polyethylene polymer, demonstrating its efficiency as catalyst in this process.

Resumo em Inglês:

Abstract This study investigates the effect of hydrothermal aging on the properties of glass fiber reinforced polymer (GFRP) rebars manufactured with isophthalic polyester or vinylester resin and glass fiber type E. The GFRP rebars were immersed in an alkaline solution (pH 12.6) for 1000 h at different temperatures (23 and 60 ºC), and their deterioration was evaluated based on microstructural and chemical changes (using SEM, DSC, XRF, and FTIR techniques), moisture absorption, and variation in mechanical properties. The results indicated an increase in the presence of voids and water absorption of the rebars with accelerated aging, with a reduction in the glass transition temperature of the resin and alteration of the chemical composition of the glass fiber. The comparison between the experimental results indicates that the rebars with matrix in vinylester resin present greater chemical resistance than the rebars with a polyester matrix. The degradation of the rebar also resulted in a reduction of approximately 6% in the tensile strength of the rebar and 2% in the modulus of elasticity. Using the damage model, it was possible to identify that the reduction in mechanical strength was associated with the simultaneous degradation of the resin and glass fiber due to the alkaline attack.

Resumo em Inglês:

Abstract The use of natural additives in biodiesel has been investigated, however, there is limited information in the literature in relation to their influence on corrosion resistance and oxidative stability. This work aims to investigate the oxidative stability of biodiesel and the corrosion resistance of carbon steel (AISI 1020) in contact with soybean biodiesel solutions (B100) in the presence and absence of natural additives such as: rosmarinic acid, curcumin, gingerol, eugenol, thymol and quercetin. Corrosion and microscopy tests were used to assess corrosion resistance. The Rancimat technique was used to study oxidative stability. The results obtained indicate that curcumin was the best additive in relation to oxidative stability, while rosmarinic acid showed better performance in inhibiting corrosion. The effect of these substances is related to the presence of phenolic compounds or the existence of oxygen in its molecular structure.

Resumo em Inglês:

Abstract The development of carbon nanotubes reinforced metal matrix composites merits relevant attention due to its capacity of improve the hardness and strength of the metal. However, the production of this kind of composite presents many challenges, such as the dispersion and adhesion of carbon nanotubes in the metallic matrix, wich may affect the composite consolidation. The present study aimed the development of composites using an age hardening aluminum alloy reinforced with 0.5 wt.% of multiwalled carbon nanotubes (MWCNT) as well as a hybrid composite based on the mixture of pure aluminum powder and the former composite. AA7050 alloy and pure aluminum matrix composites were processed by ultrasonic mixing, hot pressing and hot extrusion. Subsequently, the materials were submitted to aging heat treatments. The samples were analysed by Scanning Electron Microscopy, X-Ray Diffraction, Atomic Force Spectroscopy, Raman spectroscopy, and Vickers microhardness. It was verified the feasibility in manufacturing the composites by the powder metallurgy route proposed in this work. The AA7050 composite reinforced with 0.5 wt.% MWCNT presented higher hardness than other similar composites in the literature with higher carbon nanotubes content. The aged composite hardness increased 72% in comparison with the present one in the as extruded condition.

Resumo em Inglês:

Abstract Despite the high potential of the freeze-casting technique for production of porous inorganic substrates, there is a lack of studies on tubular geometries and their mechanical behavior under different pressure scenarios. In this work, the mechanical behavior of tubular freeze-cast alumina substrates was assessed by mathematical models from experimental O-ring tests. The stress distributions revealed a concentration of tensile stresses (within 0.2-25.0 MPa) on the plane of the load, causing brittle fracture. Furthermore, the results confirmed that the honeycomb model for brittle material adequately predicted the mechanical strength of the tubular freeze-cast substrates. Finally, fracture criteria from honeycomb model was used to estimate the maximum homogeneously distributed pressures, such as in fluids, that the substrates can withstand. This configuration represents more precisely practical conditions, though is hard to experimentaly replicate. Therefore, the developed procedure is paramount to simulate the mechanical behaviour of the tubular freeze-cast substrates under real operating conditions.

Resumo em Inglês:

Abstract The use of high permittivity materials on substrates of a microstrip antenna was developed with Bismuth Niobate ceramic doped with vanadium Oxide (BiNbO4 (V2O5)) and compared with an antenna of silicon dioxide substrate (SiO2) using Ansys software HFSS and CST Studio. The ceramic antenna has -20 dB at 3.5 GHz and the silicon dioxide antenna -24.7 dB of reflection coefficient. The bandwidth values are 80 MHz for the bismuth ceramic antenna and 100 MHz for the silica antenna. The results demonstrate that the proposed BiNbO4 antenna has great advantage compared to those mentioned in terms of volume reduction, presenting results similar to those antennas with higher volume. In addition, we use copper periodic structures (EBG) in order to increase the gain in associated with the use of BiNbO4 with addition of V2O5 on the antenna substrate leading to a reduction in the total volume. Therefore, the proposed Bismuth Niobate antenna proves to be an excellent alternative for 5G technology and microwave S band (2-4 GHz) devices, highlighting the mentioned advantages.

Resumo em Inglês:

Abstract The Vanadis® 8 is a tool steel used in the manufacture of dies, punches and tools. It has a high carbon content combined with chromium, molybdenum and vanadium, and presents good performance in its mechanical properties. Usually, its chips obtained by machining are sold to companies that use remelting. However, this technique is considered expensive and harmful to the environment. Therefore, this work aimed to analyze the efficiency of the addition of vanadium carbide (VC) and molybdenum carbide (Mo2C) in the high energy ball milling of the Vanadis® 8 steel. Microstructural analysis were performed in the pure steel and with 3% of VC and Mo2C additions. The milling parameters used were: speed of 350 rpm, ball-to-powder weight ratio of 15:1 and times of 4, 8 and 12 hours. The results indicated that the Vanadis® 8 steel milled with VC presented the best microstructural results in all of the conducted tests.

Resumo em Inglês:

Abstract The turbine blades play a crucial role in the efficiency of the steam turbines system, which can also lead to safety and economic implications in a catastrophic failure. The propagation of fatigue cracks is a relevant issue, especially if there are safety issues involving human life or the environment or significant economic losses. This work investigated the failure of a turbine blade of a 25 MW cogeneration power plant. One found several deformation marks and debris in the primary crack origin at the blade's base. They were responsible for the fretting fatigue type wear. The blade material matches the composition of X20CrMo13 steel; however, the hardness shows a higher average value (250±4.7) than typical standard values of 220–240 HB.

Resumo em Inglês:

Abstract In this work, CH3NH3PbI3 perovskite thin films were deposited by the spray-coating method in ambient conditions using different deposition temperatures and annealing times. They were then exposed to high humidity in order to investigate the relation between processing parameters and degradation mechanisms. FTIR and XRD analyses identified two degradation mechanisms, one reversible, the formation of monohydrated perovskite, CH3NH3PbI3∙H2O, and another irreversible, the decomposition of perovskite into PbI2 and CH3NH3I. It was found that perovskite degradation is very sensitive to deposition parameters and that long annealing times at high temperatures increase compound stability, retarding reversible degradation even after a long exposure to ambient conditions. This is attributed to the formation of a small amount of PbI2 during deposition that acts as a protective layer against moisture, preventing the formation of monohydrated perovskite. Additionally, no signs of dihydrated perovskite were found in the films even after 50 days of exposure to high humidity.

Resumo em Inglês:

Abstract In this work, Ag doped NaSbO3 (ANS) was successfully synthesized and applied an efficient visible light photocatalyst. The properties of catalyst were fully characterized, and DFT (the density functional theory) computation was utilized to investigate the photocatalytic mechanism. The various characterization findings proved that Ag atoms were perfectly doped into NaSbO3 crystals, which greatly reduced the band gap, and made ANS catalyst exhibit excellent visible light absorption performance. In addition, ANS appeared great photocatalytic activities and remarkable stability. Also, electrochemical characterizations illustrated that ANS possessed stronger ability of generating and transferring electrons and holes under visible light, and the doping of Ag atoms reduced the resistance of charge transfer, thus effectively accelerated the photocatalysis reaction. Moreover, through ESR characterization and scavengers coexistent experiments, •OH and •O2- were considered to be active radicals that played a crucial role in the photodegradation process. Furthermore, DFT calculation demonstrated that ANS displayed obvious visible light excitation performance via reducing the band gap. The improvement of work function enhanced the oxidation ability of photogenerated holes, forming more hydroxyl radicals, thus boosted the photodegradation of pollutants.

Resumo em Inglês:

Abstract Magnetic nanopowders were developed by functionalization of bimagnetic core@shell nanoparticles with cysteine (CoFe2O4@ɣ-Fe2O3@Cys), which present a core with high saturation magnetization (CoFe2O4) combined with a shell with high long-term chemical stability (ɣ-Fe2O3) and a sorptive L-cysteine layer. Samples of two different mean sizes were elaborated and characterized by XRD, TEM, FTIR, SER, zetametry and SQUID magnetometry. The adsorption of Pb(II) by the magnetic nanopowders was investigated as a function of pH, time, and pollutant concentration. The Langmuir model fitted well the adsorption data indicating monolayer adsorption, and a maximum adsorption capacity of 1.2 mg/g was found for pH 5. The kinetic data were well correlated to the pseudo-second-order model and the best equilibrium time was 120 min. The adsorption mechanism mainly involves electrostatic interactions in pH 5-7 and hard–soft-acid–base interactions in low pH. Moreover, the nanoparticles were recovered and reused in readsorption experiments keeping a good removal efficiency.

Resumo em Inglês:

Abstract Shielded metal arc butt welded joints for 9%Ni steel using nickel-based filler metal were analyzed by optical microscopy, scanning electron microscope, as well as transmission electron microscopy. The nanoindentation method was used to study the correlation between the structure and micromechanical properties of the fusion welded joint. The results show that there is a microstructural evolution from melted deposit to 9%Ni base steel. A significant coarse lath martensite-bainite mixture has been obtained in 9%Ni steel close to the fusion boundary while the retained austenite distributing in grain boundary of lath martensite has reduced to an undetectable level. In fusion boundary, an intermetallic layer has been observed which corresponds to the epitaxial growth of weld metal. The analysis of stress-strain behavior using nanoindentation shows that the heat-affected zone of coarse grains exhibits ductility loss and quantitative plastic deformation failure. The fusion boundary has the lowest value of yield stress while the coarse grained heat affected zone has the maximum value of yield stress.

Resumo em Inglês:

Abstract The identification of peptides that can be coupled to magnetic nanoparticles and be directed against specific receptors has been developed and applied intensively in various biomedical applications, such as magnetic resonance imaging (MRI), to diagnose neurodegenerative diseases. This work describes the properties of magnetic zero-valent iron (nZVI) nanoparticles coated with silica and subsequently decorated with a peptide as a biomarker of neuroinflammation. The synthesized nanostructured compounds were systematically characterized by XRD, SEM, AFM, DLS, FTIR and VSM techniques. Biotin-Streptavin-HRP system was carried out to confirm the peptide's anchoring to the surface of the nanoparticles. The results showed that this nanostructured compound is an excellent candidate as a contrast agent capable of being used in magnetic resonance imaging, which would optimize the diagnosis of neuroinflammatory lesions compared to current contrast media.

Resumo em Inglês:

Abstract The effect of growth conditions and post treatments on the properties of calcium phosphate films electrodeposited by a potentiostat of the authors’ design and construction is presented. The electrolyte used was formed with 0.025 M (NH4)H2PO4 and 0.042 M Ca(NO3)2.4H2O, and its pH was kept at 5. A voltametric analysis was performed to determine the necessary potential values to obtain the films. Additionally, the temperature of the electrolyte was varied to determine its influence on the properties of the deposited films. The films were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The films deposited at -1.4 V and -1.7 V present the brushite phase. The thermal post-treatment favored the formation of octagonal calcium phosphate in amorphous phase, while the basic treatment provided the OH- groups necessary for the formation of hydroxyapatite. The low cost potentiostat implemented presents excellent characteristics for obtaining films with similar characteristics to those obtained with a conventional potentiostat.

Resumo em Inglês:

Abstract The objective of the experimental work is to enhance the machining capability of electrical discharge machining by suspending equal proportion of metal powders such as, molybdenum, nickel, and chromium in EDM 30 oil. Three different control factors such as peak current, pulse on time and powder concentration were varied to analyze the response factors namely material removal rate, surface roughness and radial overcut. The cause of powders concentration on material removal rate (MRR), surface roughness (SR), and radial overcut (ROC) have been investigated. An electron dispersive spectroscopy was utilized to investigate the surface revealed the deposition of nickel and chromium in the machined surface. Machined surface was focused to atomic force microscopy and scanning electron microscopy. Analysis of variance (ANOVA) results showed that peak current is the foremost factor in affecting MRR, SR and ROC.

Resumo em Inglês:

Abstract Ti10Fe5Si5Cr3Nb composite coatings were fabricated using laser cladding technique. Laser power was varied from 800W to 1200W while the scanning speed was kept constant at 1.5 m/min. The microstructural analysis of the samples was conducted by using optical microscope, X-ray diffractometer and scanning electron microscope coupled with energy dispersive spectroscopy. Potentiodynamic polarization and diamond indenter were used to study the corrosion and microhardness properties of the alloy. The alloy exhibited a dendritic microstructure with Si-rich dispersed phase. Grain coarsening was observed to be dependent on coating depth. The microhardness was high at the top and decreased with coating depth. No improvement in corrosion resistance was noticed but the presence of Cr in the alloy promoted passivation.

Resumo em Inglês:

This study investigates the effect of aramid fabric orientation angle on the mechanical characteristics of 2-D basalt-aramid/epoxy hybrid interply composites. Hybrid laminates were fabricated by sandwiching three layers of basalt between the aramid face sheets using compression molding process. The composites were tested for tensile, flexural, interlaminar shear strength (ILSS) and Charpy impact test to understand the influence of aramid fabric orientation angle on the mechanical behaviour of hybrid composites. Results show that mechanical strengths of the hybrid laminates decline with increase in the orientation angle of aramid fabric. The (01A/03B/01A) composite possess the highest tensile, flexural, ILSS and impact properties followed by (301A/03B/301A) and (451A/03B/451A) composites. The fractured samples were analysed to identify the failure modes using scanning electron microscope (SEM) and optical microscope. The examination revealed that primary reason for (301A/03B/301A) and (451A/03B/451A) specimen failure was due to the delamination, fibre pull out and matrix crack. Strong interfacial bonding was observed between the fibre and matrix in case of (01A/03B/01A) composites.

Resumo em Inglês:

Abstract This contribution reports on an experimental polishing procedure, that is comprised of early grinding in Al2O3 slurries and late polishing in colloidal silica, which is used for preparing the nitrided region of a plasma nitrided austenitic stainless steel, for crystallographic analysis via electron backscatter diffraction (EBSD). The suitability of the polished surfaces for conducting EBSD characterization was assessed through an analysis of both the surface roughness (appraised by atomic force microscopy) and the quality of the Kikuchi diffraction patterns. We observed that as-nitrided virgin surfaces were not suitable for EBSD characterization, due to intense surface roughening, which was induced by the nitriding process itself. At the subsurface region, exposed by on-top mechanical polishing, the flatter nature of the polished surfaces allowed the acquisition of EBSD patterns with enough quality for microtexture analysis. A resolution of 100 nm in the total removed layer was attainable via careful control of the polishing parameters. Close parallelism between the polished and original surfaces was verified.