Resumo em Inglês:

Metals solidification involves the transformation of the molten metal back into the solid state. Solidification structures impact heavily on the final product's characteristics. The microstructure effects on metallic alloys properties have been highlighted in various studies and particularly the dendrite arm spacing influence upon the mechanical properties such as tensile strength has been reported. In the present investigation, Al-10wt%Si-2wt%Cu and Al-10wt%Si-5wt%Cu alloys were directionally solidified upward under transient heat flow conditions. The experimental results include solidification thermal parameters such as tip growth rate and cooling rate, optical microscopy, volume fraction of the eutectic mixture, primary dendritic arm spacing and ultimate tensile strength. Experimental growth laws of primary dendrite arm spacing as a function of the solidification thermal parameters are proposed. The Hall-Petch mathematical expressions were used to correlate the ultimate tensile strength as a function of the primary dendritic arm spacing. It was found that the alloy with higher copper content had a more refined structure. More refined structures had higher ultimate tensile strength values.

Resumo em Inglês:

Ceramic oxide coatings were fabricated on Ti6Al4V alloy by micro arc oxidation (MAO) in silicate electrolytes, with nano-TiO2 and nano-Al2O3 and without nano-additives. Effects of nano additives on the structural and mechanical properties of the MAO coatings were analysed. The MAO coatings were investigated by scanning electron microscopy (SEM), Energy-Dispersive spectroscopy (EDS) micro-hardness and linear wear test. Results show that the surface morphology and tribological properties of MAO coatings are greatly influenced by nano additives in electrolytes. After the coating treatment the surface hardness values increased from 300 HV0.1 to 635 HV0.1. The hardness tests show that nano-Al2O3 additition coating has higher microhardness values than those without any additives. The results indicated that TiO2 and Al2O3 nanoparticles into the coatings make harder and denser surface and increase the wear resistance. The wear resistance of the nano-TiO2 and nano-Al2O3 additives coatings was enhanced about 5 times than without nano additives coating.

Resumo em Inglês:

The microstructure, mechanical properties and fracture behavior of as-cast Mg-10Gd-3Y-xZn-0.6Zr (x = 0, 0.5, 1 and 2 wt%) alloys have been investigated by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and tensile tests. The experimental results reveal that the microstructure of the alloy without Zn contains α-Mg and Mg24(Gd,Y)5 phase, the microstructure of the alloy with 0.5% Zn contained of α-Mg, (Mg,Zn)3(Gd,Y) and Mg24(Gd,Y,Zn)5 phase, whereas when Zn content was 1% and 2%, the Mg12(Gd,Y)Zn phase and some needle-shaped stacking faults notably appear and the Mg24(Gd,Y,Zn)5 phases completely disappear. Moreover, a new 18R long period stacking ordered (LPSO) phase is observed in grain boundaries with increasing Zn content up to 2%. The tensile tests indicate that the alloy containing 0.5% Zn shows the optimal mechanical properties and the ultimate tensile strength (UTS), yield strength (YS) and elongation are 228MPa, 172MPa and 5.1%, respectively. As indicated by fracture analyses, the fracture modes of the alloys with 0%, 1% and 2% Zn are brittleness transcrystalline fracture, and the tensile fracture mode of 0.5% Zn alloy is typical tough transgranular fracture.

Resumo em Inglês:

Samples of ductile cast irons alloyed with Cu, Cu-Ni and Cu-Ni-Mo were austempered, borided and boro-austempered and characterized for hardness and micro-adhesive wear behavior. The kinetics of layer formation was also studied. The boriding method used was molten borax bath, in periods of 2 and 4 hours at temperatures of 850, 900 and 950 ºC. The direct austempering treatment was performed immediately following the boriding treatment (from 850, 900 and 950 ºC) using molten salt baths at temperatures of 240, 300 and 360 ºC for 4 hours (boro-austempering treatment). For comparative purposes, the conventional austempering treatment was also conducted. Optical microscopy, scanning electron microscopy, Brinell hardness measurements (on the substrate) and Vickers (on the layers) were performed, along with micro-adhesive wear tests. The boriding treatment resulted in the formation of high hardness layers, in the range of 1450 to 1750 HV, with high wear resistance. The wear resistance of borided and boro-austempered samples were increased by 40 times when compared to as cast or austempered samples, indicating the high efficiency of this type of treatment in increasing the wear resistance of this material.

Resumo em Inglês:

Silicon (Si) nanostructures were prepared in the downstream of radiofrequency SF6/O2 mixture plasma generated in 13.56 MHz hollow cathode discharge system. Depending on the oxygen percentage in the mixture, the obtained Si nanostructures were characterized for their different properties: etching rate, morphology, optical reflectance, photoluminescence, spectral response and humidity sensing. It is found that the etching rate exhibits a maximum value when the O2 ratio reaches 5%. An interesting defect-induced "violet" luminescence is reported from the Si nanostructures, whose intensity depends on their density. The obtained Si nanostructures have shown to induce a spectral response (SR) enhancement, in comparison with a smooth Si substrate, of about 100 times at 1100 nm wavelength. A very short response time (1 sec) to the humidity was measured for 5% O2 in the SF6/O2 plasma mixture, which was found to be well-correlated with the porosity of the Si nanostructures.

Resumo em Inglês:

60NiTi, despite exhibiting attractive chemical and mechanical properties desirable for biomedical applications, has not yet been processed to a porous structure suitable for general bone replacement applications. In this research, elemental Ni and Ti powders were used to process and manufacture 60NiTi parts by employing conventional press-and-sinter method. Blended Ni and Ti powders provided the possibility of liquid formation in the samples during sintering which leaded to an increase in porosity. Different processing parameters such as pressing pressure, sintering temperature, heating rate and sintering holding time were investigated in a systematic way to obtain 60NiTi parts with approximately 30 Vol.% open porosity. Further, the effects of these processing parameters on the microstructure, phase structure and dimensional stability of the as-sintered parts were investigated. Porous parts with satisfactory dimensional stability were obtained in all cases. It was found that applying lower compaction pressure, final sintering temperatures of above 942°C, faster heating rates and shorter sintering time were beneficial in terms of obtaining parts with more open porosities. Samples sintered at a final temperature of 1050°C did not contain any elemental Ni or Ti material and were ready to be solutionized to obtain hard biocompatible 60NiTi parts.

Resumo em Inglês:

The randomness of phase compositions and their distribution as well as the micro cracks and pores in refractories result in the dependence of mechanical properties on the sample size. In this work, the size effects on fracture parameters including bending strength, elastic modulus and fracture toughness of high alumina bricks were investigated by testing samples of different sizes according to the national standard in China. The results showed that the smaller samples presented higher strength, while the larger samples possessed greater elastic modulus. Weibull modulus m of bending strength for high alumina bricks calculated for samples of two sizes, each group featured 32 samples, ranged from 11 to 12, which was higher than in other refractories such as low grade high alumina, magnesia-carbon and magnesia-chrome bricks. The scatter of the average strength and its standard deviation became stable when the sample number was more than 20. The fractal dimension of fracture surface for high alumina bricks was inversely and directly proportional to the sample size and the fracture toughness, respectively. The estimated fracture toughness of high alumina bricks was close to window glass and less than alumina and mullite.

Resumo em Inglês:

A one-pot electrosynthesis platform is reported for fabrication of Y3+ doped iron oxide nanoparticles (Y-IONPs). In this procedure, Y-IONPs are electro-deposited from an additive-free aqueous solution of iron(III) nitrate, iron(II) chloride and yttrium chloride. The analysis data provided by X-ray diffraction (XRD), field emission electron microscopy (FE-SEM) and energy-dispersive X-ray (EDX) confirmed that the deposited Y-IONPs sample is composed of magnetite nanoparticles (size≈20nm) doped with about 10wt% Y3+ cations. The performance of the prepared Y-IONPs as supercapacitor electrode material was studied using cyclic voltammetry (CV) and galvanostat charge-discharge (GCD) tests. The obtained electrochemical data showed that Y-IONPs provide SCs as high as 190.3 and 138.9 F g−1 at the discharge loads of 0.25 and 1 A g−1, respectively, and capacity retentions of 95.9% and 88.5% after 2000 GCD cycling. Furthermore, the results of vibrating sample magnetometer measurements confirmed better superparamagnetic behavior of Y-IONPs (Mr=0.32 emu g-1 and HCi= 6.31 G) as compared with pure IONPs (Mr=0.95 emu g-1 and HCi= 14.62 G) resulting from their lower Mr and Hci values. Based on the obtained results, the developed electro-synthesis method was introduced as a facile procedure for the preparation of high performance metal ion doped magnetite nanoparticles.

Resumo em Inglês:

In this work, the effect of flame spraying parameters on physical, structural and microstructural characteristics of Al2O3 - 13 wt.% TiO2 (AT-13) coatings were studied. NiCrAl and AT-13 feedstock powders were used for spraying a bond coat (BC) and a top coat (TC), respectively, onto a 7075 aluminum alloy substrate. The effect of acetylene-to-oxygen ratio and the spraying distance on surface roughness, crystalline phases, porosity and thickness of top coat were analyzed. The results showed that for the evaluated spraying conditions, the volumetric oxy-fuel ratio had significant effects on roughness, porosity and crystalline phases of the coating. On the other hand, the spraying distance affected the thickness of the coating and did not influence the formation of Al2TiO5 phase; no significant effect of spraying distance on roughness was observed. The results showed that an acetylene: oxygen volumetric ratio of 1:2.5 is preferable to obtain higher melting of the ceramic powders and therefore a denser coating with major content of γ-Al2O3 crystalline phase.

Resumo em Inglês:

Photodegradation of PCL was performed exposing injected specimens to ultraviolet radiation (UV-B) up to 9 weeks. Photodegradated PCL specimens were tested by Differential Scanning Calorimetry (DSC), Infrared Spectroscopy (FTIR), mechanical properties, Optical Microscopy (MO) and Scanning Electron Microscopy (SEM).Upon exposure decrease in elongation at break and increase of elastic modulus were verified, higher degree of crystallinity was observed for longer exposure what can be due to the chemi-crystallization mechanism. From IR spectra new carbonyl group (C=O) peaks were observed. Presence of micro cracks on specimens’ surface was identified by MO. From morphological analyses is suggested that the photodegradation in PCL takes place by bulk erosion mechanism.

Resumo em Inglês:

This paper aims to evaluate the synthesis and annealing parameters for production of nanometric Bi4Ti3O12 and its properties. The powders were obtained through the solution combustion route and the impacts of annealing temperature on the materials’ physicochemical features as well as their optical and electrical properties were investigated. Thus, the prepared powders were annealed at 600ºC, 700ºC and 800ºC and then characterized by several techniques. The results demonstrated that the combustion method was effective for production of nanocrystalline powders with high levels of purity. A trend for particle and crystallite growth was observed as the calcination temperature increased. X-Ray, HRTEM and Raman spectroscopy confirmed the crystalline nature of the powders, whereas impedance spectroscopy demonstrated a reduction of electrical resistance according to the calcination temperature applied. Optical properties were not highly influenced by annealing. The temperature of 600ºC was appropriate to produce crystalline particles with desirable low sizes for application.

Resumo em Inglês:

Mn-doped CeO2 flower-like microstructures have been synthesized by a facile one-step composite-hydroxide-mediated method. The structure, morphology, optical and the surface properties of Mn doped CeO2 have been investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), UV-Vis absorption spectroscopy and X-ray photoelectron spectroscopy (XPS). The XRD results confirmed the successful incorporation of Mn into the CeO2 lattice through the formation of face-centered cubic solid solution. The photocatalytic activities of the catalysts were evaluated by measuring the photodegradation efficiency of Rhodamine B (RhB) under ultraviolet light irradiation. With an optimal molar ratio of 1% in Mn/CeO2 the highest rate photodegradation was achieved under the experimental conditions. The enhanced photocatalytic activity can be attributed to the incorporation of multivalent Mn in CeO2 promoted the separation of photogenerated charges, inhibited the recombination of photogenerated carriers, and thus prolonged the charges lifetime to participate in the photocatalytic reaction.

Resumo em Inglês:

In this work, we used mass spectrometry to investigate ammonia (NH3) formed during the nitrocarburizing and nitriding processes of α-Fe sintered and low alloy steel by using d.c. glow discharges in different N2/H2/CH4 gas concentration mixtures. Experiments were conducted using two different configurations: one to collect and analyze species probed primarily in the bulk of the plasma, at a position distant from the heated sample; and the other to collect and analyze species very close to the reactive surface of the heated sample in such a way as to allow the analysis of lower concentration or residence time species, formed at the plasma/sample surface interface. Use of these configurations contributed to the investigation of the physical chemistry involved in the above plasma processes. An exchange the expected stoichiometry in ammonia formation in N2/H2/CH4 mixtures, with a shift towards higher nitrogen consumption, is observed and is interpreted an indication of nitrogen removal from the surface associated with ammonia and carbonitrides/nitrides formation. The present results point to the existence of a correlation between the nitrocarburizing and nitriding processes with respect to the formation of non-stoichiometric ammonia as a product.

Resumo em Inglês:

The current research shows the effect of structural and morphological differences of multilayer carbon nanotubes (CNT) on radar absorbing materials (RAM) performance. Two CNT samples, from different manufacturers, had their morphological and structural aspects investigated by XRD, SEM and SEM-FEG analyses. CNT/epoxy resin based nanostructured composites were prepared and characterized by reflectivity measurements in the X-band. SEM results show the formation of agglomerates in the composites and the XRD patterns show structural differences between the two CNT samples. The best RAM performance (-25 dB) was determined for the nanocomposite based on the CNT with the smallest stacking layers (Lc = 26.9 Å) associated to the longest length of nanofilament (10-20 µm). This characteristic can have contributed to the formation of an interconnected network in the composite favoring electrical conductivity and dielectric properties, with the consequent increase of the wave attenuation.

Resumo em Inglês:

In the present work, the AISI S1 steel was pack-borided in the temperature range 1123-1273 K for 2- 8 h to form a compact layer of Fe2B at the material surface. A recent kinetic approach, based on the integral method, was proposed to estimate the boron diffusion coefficients in the Fe2B layers formed on AISI S1 steel in the temperature range 1123-1273 K. In this model, the boron profile concentration in the Fe2B layer is described by a polynomial form based on the Goodman’s method. As a main result, the value of activation energy for boron diffusion in AISI S1 steel was estimated as 199.15 kJmol-1 by the integral method and compared with the values available in the literature. Three extra boriding conditions were used to extend the validity of the kinetic model based on the integral method as well as other diffusion models. An experimental validation was made by comparing the values of Fe2B layers’ thicknesses with those predicted by different diffusion models. Finally, an iso-thickness diagram was proposed for describing the evolution of Fe2B layer thickness as a function of boriding parameters.

Resumo em Inglês:

Films of polyvinyl alcohol (PVA), Methacrylic Acid - Ethyl Acrylate (MAA:EA) copolymer and their blends PVA:MAA:EA of composition 80:20, 60:40, 50:50, 40:60, 20:80 (wt %) were prepared by using the solution cast technique. The prepared films were investigated by structural, optical and thermal studies. X-ray diffraction (XRD) scans revealed the semicrystalline nature of the blends for lower concentrations of PVA up to 60 wt % and the amorphous nature for higher ones. Fourier transform infra-red spectroscopy (FTIR) of blend samples indicates that there is a compatibility between PVA and MAA:EA copolymers through the formation of hydrogen-bonding between their polar groups.SEM image of polymer blend suggested the presence structural reorganization of polymer chains. UV-Visible spectral analysis revealed that the intensity of the shoulder around 271 nm decreases with increasing MAA:EA content. In DSC analysis, a single glass transition temperature for each blend was observed, which supports the existence of compatibility of such systems. From the observed results, 50:50 (wt %) PVA/MAA:EA is found to be the optimum blending ratio.

Resumo em Inglês:

This work was based on the surface integrity analysis of hardened steel, AISI 4317 case carburized, quenched and tempered with 58 HRC, obtained by a turning operation executed with CBN (cubic boron nitride) tool, varying three basic cutting parameters (cutting speed, feed rate and cutting depth). The surface integrity characterization was conducted analyzing the behavior of the surface roughness Ra, residual stresses and with layer presence after turning. Also, the cutting forces were measured. The experimental planning used was a central composite design. The results and data were statistically treated by the Statistica software, enabling the generation of a mathematical model, relating the dependent variables with the independent variables. The roughness values Ra obtained after the experiments ranged from 0.31 to 2.8 µm, providing an indication that is possible to replace grinding process by hard turning using CBN tools that could reduce machining time and costs. The hard turning process generated compressive residual stresses profiles and white layer formation, from 1.1 to 5.1 µm, on the surface of the samples. The penetration force showed the highest values for the turning forces measurements. The lowest values for the cutting parameters represented the optimized surface integrity of the AISI 4317 steel.

Resumo em Inglês:

In the present work niobium based complex cubic perovskite oxide Ba2AlNbO6 ceramics were produced, characterized and their stability in crude petroleum environment was studied for inert ceramic embedding used in petroleum extraction. Ba2AlNbO6 ceramic powder was prepared by means of thermo-mechanical processing. Structural characteristics of calcined material were investigated by powder X - ray diffractometry, which presented a single phase complex cubic perovskite structure with lattice parameter a = 8.3418 Å. Compacted Ba2AlNbO6 ceramics were sintered at 1150ºC during 72 hours in ambient atmosphere. The microstructure of the sintered ceramics was studied by scanning electron microscopy and mechanical behavior was studied by Vicker's micro-hardness testing. The sintered ceramics were submerged in crude petroleum for 60 days. The ceramics were taken out from petroleum periodically and subjected to structural, microstructural and mechanical characterizations. The results showed that the ceramics submerged in crude petroleum did not suffer any change at any stage of submersion. These characteristics make this material suitable for inert ceramic embedding for sensors used in petroleum extraction.

Resumo em Inglês:

To study the influence of residual stress on the corrosion behavior of welded structures, methods such as residual stress measurement, microstructure observation, and corrosion morphology observation were used. The energy transformation model and corrosion-resistance constant model were utilized to reveal the mechanism of residual stress on the welded structures’ corrosion behavior. The results show that the fusion line was the region that is most heavily affected by corrosion and sustains more serious corrosion damage than other areas, resulting in the welded structure becoming a high-incidence area for corrosion cracking and failure. Residual tensile stress could reduce the activation energy and surface atomic density, and therefore decrease the corrosion resistance of the welded structures. The residual compressive stress decreased the activation energy needed by metal atoms to convert into metal ions in welded structures, and simultaneously increased the surface atomic density. The corrosion resistance of the welded structures ultimately increased owing to the combined influence of changes in activation energy and surface atomic density.

Resumo em Inglês:

In this work, the g-C3N4 nanoparticles decorated BiFeO3 microspheres composites (g-C3N4/BiFeO3) were successfully synthesized by hydrothermal treatment of g-C3N4 nanoparticles together with BiFeO3 microspheres. The SEM and HRTEM observation indicate that the C3N4 nanoparticles with size of 30-50 nm are well decorated on the surface of BiFeO3 microspheres. The photocatalytic activities of the samples are investigated by the degradation of methylene blue (MB) under the irradiation of simulated sunlight. The as-prepared g-C3N4/BiFeO3 composites exhibit remarkable enhanced photocatalytic activity compared with bare BiFeO3. More importantly, the photocataltic performance of the composites is further confirmed by the degradation of colorless phenol. Furthermore, the favorable catalytic stability of composites is demonstrated through the recycling photocatalytic experiment. The enhanced photocatalytic activity of g-C3N4/BiFeO3 composites is mainly attributed to the separation of the photogenerated electron-hole pairs, resulting from the migration of the photoinduced charge between g-C3N4 nanoparticles and BiFeO3. A possible photocatalytic mechanism for dye degradation over g-C3N4/BiFeO3 composite is proposed based on the active species trapping experiment, revealing that the photogenerated hole (h+) and hydrogen peroxide (H2O2) are regarded as the major active species for the decomposition of dye, while hydroxyl radicals (•OH) plays a minor role in the photocatalytic reaction.

Resumo em Inglês:

Many components for aerospace and automotive industries are currently manufactured using superplastic forming, being the fine-grained aluminum alloy AA5083 widely used for this proposes. However, the development of cavitation voids is inherent in this process and reduces the ductility of the alloy. Back pressure can be used to diminish the growth of cavitation void. The experimental conditions used in this work are in the best condition for nucleation and grow of cavitation, because of the coarse grain size (81 µm), large second phase particles (9 µm) and elevated test temperature (570ºC) in a AA 5083. Domes were formed at 570ºC and at a strain rate of 5x10-5 s-1 by blow forming with and without back-pressure. They were compared in terms of their final shape, thickness distribution, and quantity of cavitation voids. The effectiveness of the usage of back pressure to reducing the quantity of cavitation void was analyzed.

Resumo em Inglês:

The superficial coatings in micro-alloyed steel pipes has been a pointed way to decrease the corrosion problems in oil and gas industry. However, little emphasis has been given to the substrate. The effects of the deposition method on the steel microstructure and properties are still not well described. In this context, this work studied the effect of Ni superalloys clads on the phase transformations, microstructure and hardness of the heat-affected zone (HAZ) of an API steel. The underestimate of the HAZ might be dangerous, since, despite the coating good corrosion performance, the substrate HAZ may present a weak region, which may lead to an in-service coating tearing. In this work, Inconel 625 and Hastelloy C276 superalloys were clad on the steel surface by a laser deposition. Dilatometry, optical and scanning electron microscopy, and computational simulation were applied. The studied steel was originally constituted by tempered martensite. The austentizing temperature had a strong influence on the austenite grain size and on the steel CCT diagram. Due to that, the laser superalloy deposits promoted a complex HAZ, where grain growth occurred. A post-cladding heat treatment was proposed to homogenize the steel microstructure and to decrease the hardness gradient at the superalloy-steel interface.

Resumo em Inglês:

Nanotexturing processes that focus on enhancing the bone-implant contact, such as electropolishing, have been proposed. The aim of this work was to evaluate the influence of Ti6Al4V surface morphology on human embryonic stem cell-derived mesenchymal progenitor (hESCs-MP) growth. Three surface treatments were used in this study: mechanically polished samples and two types of electropolished samples that were treated for 4 min and 12 min, respectively. The systems were characterized by atomic force microscopy, contact profilometry, X-ray diffraction, and wettability. Each system was submitted to a cell culture containing hESCs-MP cells for 14 days, and the resultant cell growth on each system was then evaluated. The results indicated that surfaces with higher nanometric and micrometric roughnesses experienced greater hESCs-MP cell growth in osteogenic media. The same behavior was not observed for cell growth in non-osteogenic media due to the absence of dexamethasone, which is responsible for controlling protein adsorption on the surface.

Resumo em Inglês:

In this study, composites based on polyurethane (PU) derived from castor oil and montmorillonite/polypyrrole doped with dodecylbenzenesulfonic acid (MMt-PPy.DBSA) were developed. In order to investigate the potential use of these materials for electromagnetic shielding applications, the electrical and mechanical properties of PU/MMt-PPy.DBSA composites were determined and compared with composites containing neat PPy.DBSA. The electrical conductivity of PU/MMt-PPy.DBSA composites was found to be higher than those for PU/PPy.DBSA with a similar filler content. Additionally, with a higher conductive additive content, significant increases in the tensile stress (σ) and elastic modulus (E) were observed, suggesting that MMt-PPy.DBSA acts as reinforcing agent for the PU matrix. The electromagnetic interference shielding effectiveness (EMI SE) of composites is mainly dependent on the morphology and filler content. The PU/MMt-PPy.DBSA composite containing 25 wt % of MMt-PPy.DBSA showed a maximum EMI SE of -21 dB, which is similar to the value required for commercial applications (-20 dB). The results revealed that PU/MMt-PPy.DBSA composites are promising materials for electromagnetic shielding applications.

Resumo em Inglês:

The biggest challenge for the development of carbon nanotubes polymeric nanocomposites is in the suitable dispersion and distribution of the nanometric particles along the polymer matrix. Several preparation methods have been used to obtain nanocomposites, highlighting the mixture with polymer solution followed by solvent evaporation and the hot compacting. The first one has the advantage of allowing dispersion of the nanotubes in a low viscosity medium, while the second method is more environmental favorable due to reduced use of solvent. The aim of this work was to evaluate the influence of the preparation method on the electrical resistivity of PVC/carbon nanotubes nanocomposites, containing from 0.05 to 1.00%w of carbon nanotubes. The results showed a percolation threshold of 0.4%w and 0.15%w of nanotubes for the polymer solution method and hot compacting, respectively, and an electrical resistivity reduction of eight and nine orders of magnitude, respectively, compared to pure PVC. The tensile strength of PVC/MWNT nanocomposites was not affected by the presence or content of carbon nanotubes compared to PVC without addition of nanoparticles, regardless of the material preparation method, however the deformation at beak was largely reduced.

Resumo em Inglês:

This paper studied the effect of the austenite grain refinement on the tensile and impact properties of a cast Hadfield steel (12 % Mn, 1.2 %C and 0.65 % Si). The austenite grain refinement was obtained by hafnium inoculation. Microstructural characterization showed that the Hf-refined cast Hadfield steel featured a grain size of 600 µm, while the non-refined condition presented a grain size of 3000 µm. Mechanical test results indicated that the austenite grain refinement promoted an increase in the values of the yield stress (6%), the ultimate tensile strength (37%), the toughness (88%), the work-hardening coefficient (50%) and the Charpy absorbed energy (15%). Microscopic characterization of the fractured test-pieces indicated that the grain refinement increased the proportion of plastic deformation by the twinning mechanism and furthermore improved the values of the mechanical properties of the cast Hadfield steel considerably.

Resumo em Inglês:

Secondary refining slag samples with different chemical compositions (45-54 % CaO, 7-13 % Al2O3, 20-29 % SiO2, 9-16 % MgO, 0-5 % CaF2) were investigated to verify the influence of their effective viscosity on inclusion cleanliness of DIN 38MnS6 in a steelmaking plant. The steel samples were collected during the production process for analysis of inclusions. Using the commercial software FactSage 6.4, thermodynamic calculations were performed to determine the effective viscosity, solid fraction, liquid fraction and MgO saturation point of these slags at 1560ºC. The results showed that all the slags were saturated in MgO, revealing a better protection of the ladle refractory. The addition of 2 to 5 % of CaF2 reduced the effective viscosity values for the analyzed slags from 0.45 Pa∙s to 0.10 Pa∙s , in comparison to the slags without the addition of CaF2, with an effective viscosity of 0.40 Pa∙s, 0.27 Pa∙s and 0.22 Pa∙s, decreasing the level of non-metallic inclusions for some of the analysed heats. However, it was detected during the manufacturing process that high slag fluidity and re-oxidation events continue to be a challenge associated with reducing the level of non-metallic inclusions.

Resumo em Inglês:

The main objective of the present work is to build a model and analyze the dynamic evolution process of antiphase domain boundary (APDB) in FeAl alloy. The formation, evolution of APDB, long range order (LRO), the crystal structure transition, impact of temperature on LRO, are investigated. Comparisons with experiments proves that the model is competent for the dynamic investigation of APDB in microscopic scale and able to predict different boundary-types and their corresponding atoms distribution. The dynamic process shows that the initial distribution of premier micro domains determine the morphology of APDB. The morphological evolution of APDB significantly affects the quantity of APDB. The in situ observation shows that the crystal structure of a micro domain is altered by the APDB movement. The calculated LRO revealed that the atoms in Al-sublattice mainly contribute to the low order degree of FeAl at different temperatures.

Resumo em Inglês:

The characterization of sintered valve seat inserts (VSIs) after being subjected to different heat treatment operations has been carried out. The VSIs were obtained from three different alloys by mixing iron powder with AISI M3:2, AISI M2 high-speed steels, and AISI D2 tool steel. After sintering, the VSI were quenched in air followed by double tempering at seven different temperatures. The cooling rate during air quenching was measured by means of a thermocouple type k attached to a data acquisition system. The characterization of the mechanical and physical properties of the VSIs was achieved by measuring relative density, apparent hardness and crush radial strength. The resulting microstructures for the sintered parts were interpreted using the isothermal and continuous cooling transformation diagrams for similar alloys. The VSI obtained with AISI M3:2 and AISI M2 high-speed steels after air quenching and double tempering at 600 ºC showed the best results in terms of apparent hardness and crush radial strength.

Resumo em Inglês:

PET - poly (ethylene terephthalate) - bottle surfaces were exposed to chemical agents and evaluated with middle infrared spectroscopy (MIR) and near infrared hyperspectral imaging (HSI-NIR). Images (928-2.524 nm) were acquired at different times from bottle surfaces exposed to alkaline, acidic and ethanolic media. Savitzky-Golay smoothing (2nd order polynomial and 5-point window) combined with Standard Normal Variate (SNV) was used for pre-processing data. Scores from principal component analysis (PCA) on images showed discrimination of PET according to exposure time, particularly when employing NaOH. After the first two hours of chemical exposure, significant contribution of the (-C-O + OH) combination band indicated formation of glycol ethylene on the PET surface, which was confirmed from PCA loading plots. MIR reflectance spectra ranged from 4.000 to 650 cm-1. Changes in spectral intensities could be associated with depolymerization of PET when exposed to NaOH. These were confirmed with PCA and attributed to the carboxylate group of terephthalate.

Resumo em Inglês:

In the current work, XRD, SEM, EBSD and TEM techniques were used to evaluate the microstructure of stainless Fe-Mn-Si-Cr-Ni-Co shape memory steel processed by ECAE and annealed for one hour at temperatures ranging from 650ºC to 950ºC. The results were then correlated with the mechanical and shape-memory properties of the steel. It was observed that the samples containing large grains and a microstructure free of defects or precipitates presented a high volume fraction of multi-variant thermal martensite and stress-induced martensite, resulting in good shape recovery, owing to the memory effect. The grain refinement and precipitation of second-phase particles decreased the volume fraction and number of martensite variants and considerably increased the mechanical resistance, enhancing the elastic shape recovery. It was shown that shape memory properties were essentially related to the mechanical resistance of the matrix, which in turn was related to the microstructure.

Resumo em Inglês:

This work analyzed experimental and numerically the growth kinetics of β´precipitation of a Cu-4wt.%Ti alloy after aging at 400, 500 and 600 ºC for times from 0.0166 h to 200 h. Results indicated that the precipitation process is almost controlled by nucleation and growth during aging at 400 ºC, originating a slow growth kinetics of precipitation. In contrast, the coarsening of precipitates dominates the precipitation process during aging at 500 and 600 ºC. The interfacial energy of interface between the a matrix phase and β´ precipitates was determined to be about 0.1135, 0.0980 and 0.0725 Jm-2 for aging at 400, 500 and 600 ºC, respectively. These values suggest a coherent interface which is in agreement with the flat faces of β´ cuboid precipitates. Calculated Time-Temperature-Precipitation diagram for the β´ precipitation indicated good agreement with experimental results. Precipitation hardening was higher for the slower growth kinetics of precipitation.

Resumo em Inglês:

Elastomer thermoplastics are a class of polymeric materials that received industry attention due to the possibility of joining the elastic of elastomers with the thermoplastics processability. The synergistic properties are linked to the appropriate processing. This study evaluated the effect of rotor speed during polymer mixing and the dynamic vulcanization process of polypropylene and nitrile rubber blends. Bismaleimide was employed as multipurpose agent (crosslinking coagent for peroxide and compatibilizer). Morphology, mechanical properties, compression set and oil resistance tests were evaluated for compositions containing 50 and 70 PHR of elastomer. The compatibilization of TPV was realized by infrared spectroscopy. It was shown a compatibilizer effect and better dispersion, achieving the inversion phase, only studying the effect of processing conditions (rotor speed, addition sequence, additives), without any extra interfacial agent. There is a tendency to obtain better performance with decrease speed at dynamic vulcanization or/and at torque stabilization, mainly for blends with 50 PHR of rubber.

Resumo em Inglês:

Various mechanical components such as piston, cylinder blocks, brakes and drums, have to operate under high temperature condition during their service life. Therefore, to meet the demand of high strength materials, a detailed analysis of their synthesis and high temperature tensile behaviour is of utmost importance. Present study is an effort in this direction to develop AA5052/9vol. %ZrB2 insitu composite by salt-metal reaction technique. An insitu reaction between molten aluminium alloy and two inorganic salts K2ZrF6 and KBF4 begins at 860°C and continues up to 30 min. The resulting reaction product ZrB2 is desired reinforcement confirmed by XRD analysis. Microstructural study was performed to analyse grain size, particle morphology, and their distribution in the matrix. Tensile tests were conducted at temperatures ranging from room temperature (RT) to 200°C with an interval of 50ºC. The results revealed the decreasing trend of UTS and YS (0.2% off set) with increase in temperature; however ductility increased with temperature. The composite is able to maintain about 81% of its ambient temperature strength at 150°C and 72% at 200°C. Strain hardening exponent was not significantly affected with temperature and tensile properties were correlated with fractured surface morphology examined under SEM to understand the mechanism.

Resumo em Inglês:

The dispersion of nanoparticles in nanocomposites of an epoxy matrix reinforced with alumina (10nm) and zinc oxide (100nm) is analyzed using FIB/FESEM images, varying the volumetric fraction of fillers from 0.2 % to 6.0 %. The nanofillers dispersion images were transformed to binary files and the multifractal spectrum was calculated. From these data the relation between agglomerate and individual particle dimensionalities related to the interphase percolation was investigated. Interphase percolation of nanocomposites should be achieved when the dimensionality of agglomerations is greater than the dimensionality of individual particles. The actual percolation state of the interphase is determined, matching the experimental nanocomposites behavior for electrical behavior at AC and dielectric breakdown at DC.

Resumo em Inglês:

The response to ballistic impact of alumina-ultra high molecular weight polyethylene (UHMWPE) composites with different relative concentrations of alumina was investigated. The impact tests were carried out at subsonic speed using a compressed air system. The results showed that the depth of penetration (DOP) in a Medium Density Fiberboard (MDF) bulkhead protected by a disk of the composite decreased with increasing concentration of alumina in the composite. Scanning electron microscopy (SEM) images of composites with 80 %, 85 % and 95 % alumina showed transgranular, intergranular and ductile fracture mechanisms.

Resumo em Inglês:

Blends of ultra-high molecular weight polyethylene (UHMWPE) and different contents (0, 10, 20 and 30 wt%) of linear low-density polyethylene (LLDPE) with and without maleic anhydride-grafted LLDPE (LLDPE-g-MA) were prepared by melt blending and aging resistance, thermal and mechanical properties were evaluated. The degree of crystallinity increases with the content of LLDPE in the blends. On the other hand, the addition of compatibilizer agent modifies the crystallinity and the crystallite size. Non-compatibilized blends have excellent impact resistance properties and the addition of LLDPE-g-MA aids processing but decrease the impact resistance of the blends. Thermal and mechanical properties were greatly affected by thermal and water aging. The thermal aging leads to an increase in the degree of crystallinity and consequent a decrease in impact resistance.

Resumo em Inglês:

Drying has became critical to iron ore pellet production, due to increasing inability to withdrawal moisture from the green pellets, especially faced by goethitic iron ore producers. Most of the existing pelletizing furnaces do not support increase heating rates nor changes in furnaces length, without compromise pellet quality. The present study evaluates an innovative alternative for the actual fully convective drying process composed by an up-draught drying (UDD) and down-draught drying stage (DDD), through the application of microwave energy to assist the existing process. In the present work, the process was simulated in a pot grate where industrial parameters can be simulated. The microwave generator (power input of 10 MW and 915 MHz) was connected in a traditional static pot grate at the hood by a microwave conductor. The experiments show elimination of the over-wet zone at the upper layer of pellet observed at the traditional process. A reduction greater than 7% of the moisture in UDD was achieved, while the convective process adds extra moist to the green pellets modifying the pellet shape.

Resumo em Inglês:

PHB has interesting features such as biodegradability, sustainability and durability. However, it has a high cost, in addition to being hard, brittle and thermally unstable during processing. Therefore, it was found convenient to study the crystallization of PHB/20% babassu compounds, with the intention of reducing the cost of the composite, in addition to seeking improvements in thermal properties. In this work, the parameters of melt crystallization were studied for PHB/20% babassu compounds driven at different cooling rates under a nitrogen flow. Subsequently, crystallization parameters were compared for different cooling rates. A kinetic analysis of data obtained for melt crystallization was performed. Among the models studied, Pseudo-Avrami showed the best correlation with experimental data, with discrepancy between +6% and -4%. The Mo model presented a discrepancy between +15% and -8%. A modified Mo model discrepancies are reduced to +3% and -4% within the range of validity of the model.

Resumo em Inglês:

The use of eco-friendly corrosion inhibitors in metallurgical processing has increased interest due to the reduced environmental impact. Hence, the inhibitory effect of Aniba canelilla (Lauraceae) extract was studied in the corrosion of carbon steel in 1.0 mol∙L-1 hydrochloric acid solution. This acid is used during the surface treatment of steel processing. The carbon steel protection was observed by varying the extract concentration from 50 to 300 mg∙L-1. Polarization curves revealed that this extract acted as an adsorption inhibitor decreasing both anodic and cathodic current densities. A relatively high inhibition corrosion efficiency, close to 97%, was obtained with plant stem extracts by gravimetric measurements. Weight loss measurements showed that the extract remains active for at least 72 hours at room temperature. The adsorption process of this extract is properly represented by the Langmuir isotherm. Atomic force microscopy shows that inhibited acid medium produces a smooth surface.