Performance and Surface Integrity of Ti6Al4V After Sinking EDM with Special Graphite Electrodes

Titanium and its alloys have high chemical reactivity with most of the cutting tools. This makes it difficult to work with these alloys using conventional machining processes. Electrical discharge machining (EDM) emerges as an alternative technique to machining these materials. In this work, it is investigated the performance of three special grades of graphite as electrodes when ED-Machining Ti6Al4V samples under three different regimes. The main influences of electrical parameters are discussed for the samples material removal rate, volumetric relative wear and surface roughness. The samples surfaces were evaluated using SEM images, microhardness measurements, and x-ray diffraction. It was found that the best results for samples material removal rate, surface roughness, and volumetric relative wear were obtained for the graphite electrode with 10-μm particle size and negative polarity. For all samples machined by EDM and characterized by x-ray (XRD), it was identified the presence of titanium carbides. For the finish EDM regimes, the recast layer presents an increased amount of titanium carbides compared to semi-finish and rough regimes.     

Nanostructured Systems Containing Rutin: In Vitro Antioxidant Activity and Photostability Studies

The improvement of the rutin photostability and its prolonged in vitro antioxidant activity were studied by means of its association with nanostructured aqueous dispersions. Rutin-loaded nanocapsules and rutin-loaded nanoemulsion showed mean particle size of 124.30 ± 2.06 and 124.17 ± 1.79, respectively, polydispersity index below 0.20, negative zeta potential, and encapsulation efficiency close to 100%. The in vitro antioxidant activity was evaluated by the formation of free radical ·OH after the exposure of hydrogen peroxide to a UV irradiation system. Rutin-loaded nanostructures showed lower rutin decay rates [(6.1 ± 0.6) 10⁻³ and (5.1 ± 0.4) 10⁻³ for nanocapsules and nanoemulsion, respectively] compared to the ethanolic solution [(35.0 ± 3.7) 10⁻³ min⁻¹] and exposed solution [(40.1 ± 1.7) 10⁻³ min⁻¹] as well as compared to exposed nanostructured dispersions [(19.5 ± 0.5) 10⁻³ and (26.6 ± 2.6) 10⁻³, for nanocapsules and nanoemulsion, respectively]. The presence of the polymeric layer in nanocapsules was fundamental to obtain a prolonged antioxidant activity, even if the mathematical modeling of the in vitro release profiles showed high adsorption of rutin to the particle/droplet surface for both formulations. Rutin-loaded nanostructures represent alternatives to the development of innovative nanomedicines.     

Corrosion-Erosion Effect on TiN/TiAlN Multilayers

The goal of this work is to study electrochemical behavior under corrosion-erosion conditions for [TiN/TiAlN] _n multilayer coatings with bilayer number (n) of 2, 6, 12, and 24 and/or bilayer period (??) of 1500, 500, 250, 150, and 125?nm deposited by a magnetron sputtering technique on Si (100) and AISI 1045 steel substrates. The Ti-N and Ti-Al-N structures for multilayer coatings were evaluated via x-ray diffraction analysis. Silica particles were used as the abrasive material in corrosion-erosion tests within the 0.5?M H₂SO₄ solution at impact angles of 30° and 90° over the surface. The electrochemical characterization was carried out using the polarization resistance technique (Tafel) to observe changes in corrosion rates as a function of the bilayer number (n) or bilayer period (??) and impact angle. Corrosion rate values of 359?mpy of uncoated steel substrate and 103?mpy for substrate coated with n?=?24 (???=?125?nm) under an impact angle of 30° were found. On the other hand, with an impact angle of 90° the corrosion rate exhibited 646?mpy on uncoated steel substrate and 210?mpy for substrate coated with n?=?24 (???=?125?nm). This behavior was related to the curves of mass loss for both coated samples and the surface damage was analyzed via SEM images for the two different impact angles. These results indicate that TiN/TiAlN multilayer coatings deposited on AISI 1045 steel are a practical solution for applications in erosive-corrosive environments.     

Crack healing in liquid-phase-pressureless-sintered silicon carbide–aluminum nitride composites

Crack healing in liquid-phase-pressureless-sintered SiC–AlN composites was investigated by introducing cracks into specimens and subsequently heat-treating the specimens. It was observed that cracks were healed and the strength was recovered. Cracks were filled with silica or mullite produced by the oxidation of the composites. It was shown that the healing temperature could be fixed in the range 1100–1300 °C and that large cracks up to about 300 μm could be healed completely. Our results imply that a simple oxidation heat-treatment can improve the reliability of silicon carbide–aluminum nitride components.     

Application of GPR in the Study of a Modern Alluvial Megafan: The Case of the Taquari River in Pantanal Wetland,West-Central Brazil

A novel and timely ground penetrating radar (GPR) survey has been carried out in Pantanal from Mato Grosso State, west-central Brazil. Fieldwork was carried out on February/2001 and August/2002 in an attempt to understand avulsion processes that are occurring within Taquari alluvial megafan. The main objectives were to map channel, crevasse and floodplain morphology, as well as active sedimentary bedforms. Many GPR profiles were acquired in the medium and lower Taquari River course. Subaqueous megaripples and exposed sand bars were identified in the medium fan area. Similar features were observed in the lower fan channels, where there were many crevasses in the marginal levees. During the flooding seasons, the flow splays out on to the floodplain, where new distributary channels are being formed. GPR data show that the lower fan, Taquari channel is topographically higher than the adjacent floodplain, thus favoring avulsion as a natural process of river course shifting. GPR data obtained during the wet and dry seasons, together with sedimentology information have been very important in characterizing the fluvial dynamics, and avulsion phenomena.     

Improvement of Electrochemical Surface Properties in Steel Substrates Using a Nanostructured CrN/AlN Multilayer Coating

Improvement of corrosion properties on AISI D3 steel surfaces coated with [CrN/AlN] _n multilayered system deposited for various periods (Λ) via magnetron sputtering has been studied in this work exhaustively. For practical effects compared were the latter properties with CrN and AlN single layers deposited with the same conditions as the multilayered systems. The coatings were characterized in terms of crystal phase; chemical composition, micro-structural, and electrochemical properties by x-ray diffractometry, energy dispersive x-ray, Fourier transforming infrared spectroscopy, atomic force microscopy, scanning electron microscopy, Tafel polarization curves, and electrochemical impedance spectroscopy. Corrosion evolution was observed via optical microscopy. Results from x-ray diffractometry analysis revealed that the crystal structure of [CrN/AlN] _n multilayered coatings has an NaCl-type lattice structure and hexagonal structure (wurtzite-type) for CrN and AlN, respectively, i.e., it was made non-isostructural multilayered. The best behavior was obtained by the multilayered period: Λ = 60 nm (50 bilayers), showing the maximum corrosion resistance (polarization resistance of 1.18 KΩ, and corrosion rate of 1.02 mpy). Those results indicated an improvement of anticorrosive properties, compared to the CrN/AlN multilayer system with 1 bilayer at 98 and 80%, respectively. Furthermore, the corrosion resistance of steel AISI D3 is improved beyond 90%. These improvement effects in multilayered coatings could be attributed to the number of interfaces that act as obstacles for the inward and outward diffusions of ion species, generating an increment in the energy or potential required for translating the corrosive ions across the coating/substrate interface. Moreover, the interface systems affect the means free path on the ions toward the metallic substrate, due to the decreasing of the defects presented in the multilayered coatings.     

THE LAMINAR FLOW TUBULAR REACTOR WITH HOMOGENEOUS AND HETEROGENEOUS REACTIONS II. Application to Reactor Modeling Involving Free Radical Reactions

The simulation of the complex polychlorination of methane in a non-isothermal photoreactor with laminar flow regime shows the usefulness of the integral equations deduced in Part I of this contribution. Improved iterative schemes for numerical solution have been implemented by using the particular equations proposed for species having slow, very fast and instantaneous reaction regimes.

From such integral equations, in a mathematically consistent form, deviations in the fields of predicted concentrations with and without the application of the local steady-state approximation for homogeneous reactions involving atomic and free radical species have been obtained. Similarly the fields of predicted concentrations applying the usual assumption of negligible wall reactions for the same highly reactive intermediate species has been compared with the reaction mechanisms that includes the wall reactions. A comprehensive analysis of the validity of these simplifying assumptions is presented.     

Moderate,but Not Excessive,Training Attenuates Autophagy Machinery in Metabolic Tissues

The protective effects of chronic moderate exercise-mediated autophagy include the prevention and treatment of several diseases and the extension of lifespan. In addition, physical exercise may impair cellular structures, requiring the action of the autophagy mechanism for clearance and renovation of damaged cellular components. For the first time, we investigated the adaptations on basal autophagy flux in vivo in mice’s liver, heart, and skeletal muscle tissues submitted to four different chronic exercise models: endurance, resistance, concurrent, and overtraining. Measuring the autophagy flux in vivo is crucial to access the functionality of the autophagy pathway since changes in this pathway can occur in more than five steps. Moreover, the responses of metabolic, performance, and functional parameters, as well as genes and proteins related to the autophagy pathway, were addressed. In summary, the regular exercise models exhibited normal/enhanced adaptations with reduced autophagy-related proteins in all tissues. On the other hand, the overtrained group presented higher expression of Sqstm1 and Bnip3 with negative morphological and physical performance adaptations for the liver and heart, respectively. The groups showed different adaptions in autophagy flux in skeletal muscle, suggesting the activation or inhibition of basal autophagy may not always be related to improvement or impairment of performance.     

Macrosegregation and microstructure dendritic array affecting the electrochemical behaviour of ternary Al–Cu–Si alloys

The aim of the present study is to evaluate the electrochemical corrosion behaviour of ternary as-cast Al–Cu–Si alloys. Electrochemical impedance spectroscopy (EIS), potentiodynamic anodic polarization techniques and an equivalent circuit analysis were used to evaluate the corrosion resistance in a 0.5 M NaCl solution at 25 °C. It was found that silicon and copper contents, which are affected by position in casting due to macrosegregation, and the dendrite arm spacing, can play an interdependent role on the corrosion behaviour. For the region with predominant Cu inverse segregation, i.e., close to the casting surface, the Cu content is the driving-force leading to a decrease in the corrosion resistance, but the favorable effect of the fineness of the dendritic array has also to be taken into account. However, from secondary dendrite arm spacings of about 15 μm up to coarser dendritic arrays, the Si particles seem to be the driving-forces related to the corrosion resistance and for these cases coarser microstructures were shown to improve the corrosion resistance.