Scielo RSS <![CDATA[Materials Research]]> vol. 21 num. 4 lang. en <![CDATA[SciELO Logo]]> <![CDATA[Solution Treatment Behaviors of 6061 Aluminum Alloy Prepared by Powder Thixoforming]]> Powder thixoforming (PTF) was a promising processing technology that can be used to fabricate high strength particle reinforced aluminum matrix composites, and a pioneer 6061 matrix alloy was fabricated utilizing PTF to investigate its solution treatment behaviors. A comparison study with traditional permanent mold cast (PMC) 6061 alloy disclosed that PTF alloy showed significantly reduced pore amount with only 0.16% (3.50% for PMC alloy). During solution treatment, PTF alloy displayed a much quicker solutionization progress than PMC alloy because of coarse eutectic phases and primary dendrites in latter alloy, its peak values of 14.5%, 241 MPa and 195 MPa in elongation, ultimate tensile strength and yield strength were achieved at 560ºC, an enhancement of 81.3%, 33.9% and 97.0%, respectively, compared with as-fabricated alloy. The dissolution of eutectic phases plays a dominative role in the growth of the primary α phases and secondarily primary α phases within 535ºC. However, the coarsening after 535ºC is subject to a mixture model involving atom diffusion along grain boundaries and through the crystal lattice. The superior tensile strengths of PTF alloy than PMC alloy resulted from decreased grain size, enhanced solid solution strengthening, reduced porosities and decreased harmful effect of insoluble phases in PTF alloy. <![CDATA[The Effect of Controlled Shot Peening on the Microstructure and Fatigue Behavior of Wet Copper-Based Powder Metallurgy Friction Plates]]> The effects of shot peening treatments on the microstructure and fatigue behavior of the teeth root in wet copper-based powder metallurgy friction plates were investigated and an efficient method for selecting optimal shot peening parameters for friction plates was proposed. Different experimental processes including microscopy observation, microhardness, roughness and X-ray diffraction measurements have been performed to characterize the treated surface of specimens. It is found that fatigue life of friction plates firstly increases and then decreases with the increase of Almen intensity, and the optimal fatigue life has improved over 55%. It is considered that both surface grain refinement and high residual compressive stress are the main ingredients responsible for the improved fatigue life. With further increase of Almen intensity, surface roughness of the teeth root gradually increases to a critical point, where rough peened surface may induce crack initiation due to stress concentration, and finally lead fatigue deteriorate. <![CDATA[Numerical Analysis of Twin-Roll Casting of Strips With Profiled Cross-Section]]> The relatively high production costs of innovative materials with tailored properties such as Tailor Welded Blanks, Patchwork Blanks, Tailor Heat Treated Blanks and Tailor Rolled Blanks are responsible for a growing interest in new cost-effective production methods. One of the promising energy-saving and environmental friendly technologies for the production of tailored blanks is twin-roll casting. In the study a new alternative method for twin-roll casting of strips with profiled cross-section is proposed, which uses one or more preloaded endless steel strips with an antiadhesive coating for profiling of the formed strip on a pair of the common cylindrical shells. As a primary stage for the practical process design, numerical simulation of the process using the finite element software package ANSYS is realized. In this way, dependencies of the strip elements outlet temperature, deformation zone length and elements outlet speed on the varied strips thickness and total solidification-deformation zone length are established. Based on the simulation results, a procedure for the twin-roll casting process design is suggested. <![CDATA[Preparation, Characterization and Photostability of Nanocomposite Films Based on Poly(acrylic acid) and Montmorillonite]]> Polyacrylic acid (PAA)/clay mineral (SWy-1) nanocomposites were prepared by intercalation in solution and their photostability was evaluated. For the nanocomposite films containing 5, 10 and 20 wt % in SWy-1 mass occurred intercalation along with some clay exfoliation, while for PAA/30%SWy-1, the intercalation of PAA chains into the clay interlayers was observed. Scanning Electron Microscopy (SEM) images of the films suggested that nanocomposite films are homogeneous, indicating efficient dispersion of the polymer matrix into the SWy-1 clay. The thermal degradation temperatures of depolymerisation for the nanocomposite films were higher (362-370 °C) than pure PAA (361 °C), which means that the presence of SWy-1 clay promotes thermal stabilization.The photooxidative degradation of pure PAA and nanocomposite films was followed using Size Exclusion Chromatography (SEC). The degradation rate constant for pure PAA was higher than nanocomposite films; therefore, the increase of SWy-1concentration detained the degradation of PAA. The presence of SWy-1 clay contributes for the photostabilization of the material. SWy-1 has ability to disperse the incident light as well as also to absorb part of the UV light instead of PAA, hence minimizing the degradation rate. <![CDATA[Lubricated Conditions Imposed on Coating Multi-layer on Wear Resistance Under Cr<sub>2</sub>O<sub>3</sub> Effect]]> Lubricated pin-on-disk sliding wear tests were performed on applied to Al-0.1Mg-0.35Ni-Si Alloy by using the spray coating method has been investigated. Different loads were 5, 10, and 15 N at a sliding velocity, 1.32 m/s at room temperature and 60% relative humidity. The surfaces were analyzed by using X-ray diffraction the residual (XRD), energy dispersive (EDS), scanning of (SEM) and (AFM), respectively. The results have showed that the thickness of Cr2O3 coating was significantly related under the identical cold spray condition. These methods have contributed much of the understanding of quality and properties of surfaces. The (Cr2O3) coating has great potential as a wear-resistant. The hardness increased from 102 ± 5 HV to 116.4 ± 2.5 HV at coating thickness 45 µm and friction coefficient reduced from 0.29 to 0.24; and the wear rate was about 2.11X10-13 m3N-1m-1 while hardness was increased from 102 ± 5 HV to 108 ± 3.5 HV at coating thickness 15 µm. The friction reduced from 0.31 to 0.29 at same coating thickness alloys, and the wear rate was about 2.73X10-13 m3N-1m-1. The tribological properties of Cr2O3 coating have exhibited low friction and beneficial to improve the adhesion which was clear on worn surfaces of Cr2O3 coating. Crack, powder flocculation and powder formation are caused by the wear mode of the surface. Brittle fracture was found; while, adhesion and oxidation are the main mechanism of wear during the test. <![CDATA[Kinetics of Vacancy Doping in SrTiO<sub>3</sub> Studied by <em>in situ</em> Electrical Resistivity]]> The kinetics of annealing to transform stoichiometric SrTiO3 insulator into a vacancy-doped semiconductor-superconductor was revisited by in situ electrical resistivity measurements. SrTiO3 single crystals were grown by Floating Zone Method. Using a homemade apparatus several electrical resistivity as a function of time were measured at different temperatures, which allows one to study the creation of vacancies during annealing under vacuum. The activation energy for the oxygen vacancies formation/charge doping in SrTiO3 was estimated as 1.4±0.3 eV using solid-state kinetics approach. <![CDATA[Novel Route for Fabrication of ZnO nanorods-Au Nanoparticles Hybrids Directly Supported on Substrate and their Application as Gas Sensors]]> The aim of this study was to develop a novel, simple and fast route to prepare ZnO nanorods (NRs) -Au nanoparticles (NPs) hybrids directly supported on a substrate to be used in gas sensor devices. The ZnO NRs were promptly grown on interdigitated Au electrodes Al2O3 substrates by chemical bath deposition at a low temperature. After that, Au NPs were deposited by sputtering. Results obtained by XRD, SEM, EDX and TEM showed the perpendicularly aligned growth of the ZnO NRs with a hexagonal base on the substrate and the Au NPs homogeneously covered the ZnO NRs surface. The ZnO NRs-Au NPs hybrids-based sensor exhibited an improved sensor response for H2 and O2 gases compared to the ZnO NRs at 300 ºC. Due to the ability to prepare homogeneous hybrids with high surface directly supported on the substrate; the developed route might provide a convenient approach to preparing gas sensor devices. <![CDATA[Thermomechanical Modelling of FSW Process Using a Cylindrical Tool in an Aluminum Alloy Alclad AA 2024-T3]]> The Friction Stir Welding Process (FSW/P) is an innovative technique to join metals using the plasticity, not occurring the melting. It was initially applied in aluminum alloys, but recently it has been extended to other materials, for example, copper, steel alloys, polimers and others. In this work it is analyzed the thermo mechanical modelling of the energies involved in the FSW process, performed using AA2024-T3 Alclad aluminum alloy. The temperature of the process surface was also calculated in the interval where it was not measured by type k thermocouples, visual inspection, forging force and energy per weld length analysis were also performed. The equations developed in this work were able to describe the behavior found in the experimental data of temperature and energy per weld length, which allows concludes that can be used to define any temperature point in a region of interest. <![CDATA[Transport Properties of Polycrystalline Mixed Copper-Zinc Ferrites]]> Polycrystalline mixed Cu-Zn spinel ferrites with general formula Cu1-xZnxFe2O4 (x = 0.0, 0.1, 0.3, 0.5 and 0.7) have been prepared by solid-state reaction method. The effect of Zn2+ ions on transport properties such as DC and AC resistivity, dielectric constant and dielectric loss tangent has been presented in this paper. The resistivity increases with Zn content and decreases with frequency which have been explained by Verway's hopping mechanism. Decrease of DC electrical resistivity with increasing temperature has been observed and activation energy has been found to increase with increasing Zn content. The dielectric constant is found to decrease with increasing Zn content as well as increasing of frequency has been explained on the basis of space charge polarization. In this communication, an attempt has been made to explain the conduction mechanism of Cu-Zn ferrites on the basis of electronic hopping frequency between Fe2+ and Fe3+ ions. <![CDATA[Identification of Humidity Sensing Mechanism in MgAl<sub>2</sub>O<sub>4</sub> by Impedance Spectroscopy as Function of Relative Humidity]]> MgAl2O4 is a humidity sensing material, which high melting point requires high sintering temperatures. In this work, manganese oxide was used as a sintering aid to obtain MgAl2O4 samples sintered at 1350°C with a microstructure suitable for humidity sensing. Impedance spectroscopy analyses were performed at several levels of relative humidity, indicating that this correlation is possible within the range of 10-80% of relative humidity. <![CDATA[Designing a Microstructural Array Associated with Hardness of Dual-phase Cu-Zn Alloy Using Investment Casting]]> A comparative investigation on the microstructural morphologies and hardness values of Cu-35 wt.% Zn and Cu-30 wt.% Zn with 1.5 wt.% Al content is provided. Distinctive specimens by using traditional investment casting were produced. Specimens withdrawn from distinct locations along the castings were thermally and microstructural analyzed. Thermally and chemically induced microstructural modifications affecting the microstructure and hardness are discussed. It is found that components (specimens) located at different positions along of the pattern tree casting have distinctive hardness values. This is associated with Cu segregation and cooling rate. It is also found that solidified piece under a cooling rate ~0.12 K/s has hardness 20% higher than the specimen solidified under 0.07 K/s. Duplex brass with Widmanstätten structure constitutes the resulting microstructure array. This seems to be associated with Al content, while both Zn and Al contents are associated with cooling rate as responsible parameter to induce Widmanstätten structure formation. <![CDATA[Band Structure, Charge Distribution and Optical Properties of AlP<sub>x</sub>Sb<sub>1-x</sub> Ternary Semiconductor Alloys]]> The present contribution studies on the composition dependence of the electronic and optical properties of the zinc-blende alloy system AlPxSb1-x. The calculations are performed using a pseudopotential approach under the virtual crystal approximation. Features such as electronic band structure, energy band-gaps, refractive index, dielectric constants and valence and conduction charge densities are determined and their compositional dependence are examined and discussed. The aim of this paper is to provide new data for electronic and optical properties by varying the alloy composition x and to see to what extent the compositional disorder affects the properties of interest. The effect of alloy disorder on the energy band-gaps and electron charge densities is found to be important for getting a meaningful agreement with experiment. Our results show a direct-band gap bowing parameter of 2.7 eV which agrees very well with experiment. Moreover, a transition between indirect band gaps is found to occur twice. Besides, bonding and ionicity are discussed in terms of electron charge distribution. The information derived from the present study can be useful for optoelectronics applications. <![CDATA[Colocid Dye - A Potential Corrosion Inhibitor for the Corrosion of Mild Steel in Acid Media]]> Corrosion inhibition nature of Colocid dye on the corrosion of mild steel in acid media was analyzed using weightloss and electrochemical methods. The results of electrochemical and weightloss studies indicated that Colocid acid could act as a potential inhibitor for mild steel in acid media. It has been observed that the inhibition efficiency increases with inhibitor concentration and the inhibition efficiency of Colocid acid dye for the corrosion of mild steel in 1.0 M HCl solution is larger than that in 0.5 M H2SO4 solution.Potentiodynamic polarization studies showed that the dye molecule is of mixed type inhibitor. The adsorption of the compound on the mild steel surface obeyed Langmuir adsorption isotherm. The potential of zero charge was measured to find corrosion inhibition mechanism in these media. <![CDATA[The Iron Sulfides Crystal Growth from the Halide Melts]]> A new approach to a single crystals growth of the iron sulfide phases of definite structure and nonstoichiometry is developed and applied. This approach is based on the method of crystal growing from solution melts. This approach is based on the crystallization or recrystallization of iron sulfides from iron sulfide solutions in iron dihalide melts under fixed sulfur vapor pressure in the closed system in non-isothermal (two-temperature) conditions. It allows to regulate the composition and structure of the resulting iron sulphide. In particular, at a relatively low pressure (&lt;0.4 atm), pyrrhotite with a trigonal 3T structure is synthesized. At higher pressure pyrite β-FeS2 is grown. Reaction scheme for the formation of iron sulphides based on the reversible oxidation of sulfur by iron dihalide is proposed and substantiated. On the base of the {pyrite + marcasite} - mixture annealing under the melts of the deepest eutectic compositions of KCl - FeCl2 and NaCl - KCl - FeCl2 systems, the instability of the marcasite phase regarding the pyrite one (at least, for T ≥ 340°C) was shown. <![CDATA[Biodegradation of Poly (3-hydroxybutyrate) /Eggshellsystems]]> In this work, biocomposites of poly (3-hydroxybutyrate) (PHB) / calcium carbonate from Rhea Americana eggshells were prepared and the effects of the addition of the inorganic filler in the polymeric matrix were assessed. The residue (powder) of the eggshell calcined at 400 ºC or in natura was inserted into a PHB solution for preparation of films via casting. Powder samples were characterized by X-Ray Fluorescence (XRF), X-Ray diffraction (XRD) and Thermogravimetry (TG/DTG) and films were characterized by X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM) and biodegradation tests according to the ASTM G 160-03 norm: the results were reported as weight loss and visual inspection by optical microscopy (OM). From the results of the XDR, it was perceived that the peaks in the diffractograms of the powder obtained by milling the Rhea Americana eggshells corresponded to the diffraction patterns of the Calcite crystals, which is a calcium carbonate polyform, and that the calcination preserved the crystalline structure, maintaining the calcium carbonate in the samples. For the biocomposites, a peak characteristic to the calcium carbonate in 29.57º was detected, indicating the insertion of the filler to the polymer matrix. Through SEM the presence of small agglomerates, probably due to polymer particles that were not dissolved, was observed for the pure PHB film. With the addition of the filler in natura a greater porosity was formed in the surface of the biocomposite films, and with the calcined filler, homogeneous films with reduced porosity were obtained. From the weight loss and OM results, it was observed that the filler inserted into the polymeric matrix catalyzes the biodegradation process up to 60 days evaluation in different ways, depending on the type of sample used. <![CDATA[On the Machinability and Surface Finish of Superalloy GH909 Under Dry Cutting Conditions]]> GH 909 alloy is a kind of low thermal expansion superalloy with high strength and low expansion coefficient. It is mainly used for manufacturing of aero-engine turbine casings, sealing ring, vanes and other gap control parts, to improve the working efficiency and thrust of the engine as well as to reduce gas loss and fuel consumption. However, the machinability is still a problem that restricts the application of GH909. This paper investigated the machinability referring to cutting forces, surface quality and tool wear in the milling process with carbide tool. The main conclusions are: (1) GH909 has similar machinability with other Nickel-based alloys, cutting velocity does not have great influence on cutting forces for small radial cutting depth. (2) Good machined surface quality can be get for cutting velocity around 70m/min. (3) To get good tool performance and reduce tool wear rate, cutting velocity can be set to no larger than 80m/min. <![CDATA[Erratum: Influence of Austenitizing on the Mechanical Properties of Maraging 300 and Sae 4340 Steels - Comparative Study]]> GH 909 alloy is a kind of low thermal expansion superalloy with high strength and low expansion coefficient. It is mainly used for manufacturing of aero-engine turbine casings, sealing ring, vanes and other gap control parts, to improve the working efficiency and thrust of the engine as well as to reduce gas loss and fuel consumption. However, the machinability is still a problem that restricts the application of GH909. This paper investigated the machinability referring to cutting forces, surface quality and tool wear in the milling process with carbide tool. The main conclusions are: (1) GH909 has similar machinability with other Nickel-based alloys, cutting velocity does not have great influence on cutting forces for small radial cutting depth. (2) Good machined surface quality can be get for cutting velocity around 70m/min. (3) To get good tool performance and reduce tool wear rate, cutting velocity can be set to no larger than 80m/min.