Materials Science Forum Vol. 1012

Abstract: The contact between fuels and various metals used in vehicles make them susceptible to corrosion. Aluminum is a metal widely used in automotive components owing to its corrosion resistance as well as mechanical properties. The ABNT 14359 standard establishes a method for determining fuel corrosion; however, it is restricted to copper and fossil fuels. In this standard, corrosion is assessed qualitatively by visual comparison of patterns, which can lead to uncertain results. The methodology used in this study involves the immersion of metallic materials in fuels for a specific period of time for further analysis by scanning electron microscopy (SEM), and electrochemical analysis by electrochemical impedance spectroscopy (EIS) and anodic potentiodynamic polarization (APP). The results indicated that aluminum alloy AA 3003 is suitable for use in the production of vehicle components that will be in contact with biodiesel, diesel, ethanol, or gasoline, since no serious case of corrosion occurred.

Abstract: In this work the calibration of an Alternative Current Potential Drop (ACPD) system was performed to monitore laboratory mechanical tests on marine environment under cathodic protection. The calibration was done on CT type specimens of API 5L X65 steel dimensioned according to ASTM E1820 standard., The crack propagation during a tensile test with displacement control in an ACPD equipment was monitored through the performs points collection by two channels: one that monitors the crack growth and another that monitors a region free of crack. Using a profile projector and graphical data processing and analysis software, the area of ​​the fracture surface of the specimen was meansured, which allowed to correlate a crack size with a corresponding value of potential drop and the calibration curve. In order to verify verify the efficacy and precision of the technique, step loading tests were performed on API 5L X65 steel test specimens, submerged in synthetic sea water under the overprotection potential of-1300mV_Ag/AgCl. The results of the calibration showed few dispersed errors, and the main factors of this dispersion may be related to the geometry of the specimen and with variations in current flow density, which is influenced by corners and edges and by the presence of pick-up inductive. The calibration and its effectiveness can be verified through the results of the tests in marine environment, presenting crack lengths close to the actual values, confirming the effectiveness of the ACPD technique.

Abstract: The purpose of the plasma oxidation process is to increase the hardness, corrosion resistance and to improve the biocompatibility properties of Ti6Al4V alloys by thickening the natural oxide in the material, which is produced by this treatment. The aim of this work is to verify the effect of temperature on the thickness, hardness and wear resistance of the Ti6Al4V alloy treated with plasma oxidation. The treatment was performed using a Pulsed DC vacuum reactor, with a gas ratio of 60% Ar and 40% O₂ and 1.65 torr pressure for 1 hour of treatment, at temperatures of 480°C, 520°C, 670°C and 705°C. In regards to the multilayer formation of anatase and rutile, it was observed that the layer thickness increased as the treatment temperature increased. The increase of surface hardness provided by the treatment caused a considerable increase in the wear resistance of the studied material. The greatest layer thickness and surface hardness were obtained for the material treated at 705°C, but the lowest wear volume was obtained for the material treated at 520°C.

Abstract: Investigations have been performed to study the effects of the electrolyte composition on the properties of anodized films grown on AZ31B magnesium alloy. The corrosion protection ability of the oxide layers was explored by using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy. Film morphology was examined by scanning electron microscopy and confocal laser scanning microscopy. In spite of its higher roughness average, the film formed in the silicate and hydroxide mixed solution enhanced the protective properties of the anodized layer, thus reducing the substrate dissolution rate.

Abstract: Is the concern with latent phenomenon of sensitization, as it exposes austenitic stainless steels to one of the most severe types of corrosion, intergranular, caused by chrome impoverishment in some regions after the material has been treated thermally in a temperature range between 450°C and 850°C. The aim of this study is to identify the conditions under which the stainless steel AISI 304 austenitic will sensitize, microstructural analysis and reactivation potentiodynamics technique by Double cycle method (DL-EPR). In steel samples were subjected to different ranges of time and temperature. The behavior of the degree of sentiment reveals that the rainfall happens so intense under the conditions under study with the exception of 900oC - 1, 2, and 6, which was observed and proven both by microstructural analysis and the DL-EPR.

Abstract: Corrosion rate behavior of laser welded dual-phase galvanized steel, DP 600, has been assessed in comparison with the material without the laser weld, in 3.5% NaCl solution. Three combinations of both scanning speed and laser power parameters were selected, maintaining the thermal input of 30 J mm^-1, calculated as the ratio between the laser beam power [W] and the scanning speed [mm s^-1]. The corrosion studies included measurements of open circuit potential, micro and macro polarization, showing higher corrosion rates as scanning speed decreased. Optical microscopy showed the formation of a grain size refined morphology in the heat affected zone and fusion zone. A mechanism has been proposed to explain the corrosion behavior as a function of the laser parameters, which dictated the galvanized coating vaporization.

Abstract: The aim of this study was to investigate and compare the relationship between corrosion resistance and roughness in the samples of carbon steel SAE 1020 and DOMEX^® 700 MC steel. Surfaces with different roughnesses were compared. The metal alloys were analyzed via electrochemical impedance spectroscopy (EIS), anodic potentiodynamic polarization (APP), roughness tester and scanning electron microscopy (SEM). It was observed that the samples exhibited different behavior with respect to corrosion resistance, according to the surface conditions and materials that were tested. The lowest roughness values represented the best results in the electrochemical tests. The samples of carbon steel with lower maximum depth of valleys (Rv) showed the best protection properties compared to other samples.

Abstract: The in situ chemical deposition of polypyrrole (Ppy) in presence of different concentrations of salicylic acid (SA) directly at copper 99.9% surface in ethanol solution using hydrogen peroxide as catalyst was studied. In all the concentrations, 50.0, 25.0, 12.5 and 6.25 mmol L^-1 the polymerization was possible. The layer formed on the copper surface showed to be adherent and homogeneous. Its morphology presented as compact microspheres. The polarization curves showed a positive displacement in the corrosion potential of copper with undoped Ppy when compared to the polished copper surface. Copper surfaces containing doped Ppy-SA also showed an increase to the positive direction in the corrosion potential and the corrosion current density decreases more sharply in the presence of SA as dopant. These results indicated that Ppy+SA can act as a protective layer on copper surface and improve the corrosion protection. The protection efficiency of the coating was Cu surface < Cu+Ppy < Cu+Ppy+SA 50.0 < Cu+Ppy+SA 25.0 < Cu+Ppy+SA 12.5 < Cu+Ppy+SA 6.25 mmol L^-1.

Abstract: Metal coating films were deposited on the surface of the pieces of non-conducting polymers, acrylonitrile butadiene styrene (ABS), high impact polystyrene (HIPS) and poly (lactic acid) (PLA). These three polymers have been used since they are the main raw materials available for fusion and deposition molding equipment. In order to achieve surface metallization by electrodeposition, it was necessary to apply a pre-treatment using the chemical polymerization technique in solution with the electroconductive polymer polypyrrole (PPy) was deposited on the specimens. A uniform layer of PPy was deposited on the surface of the specimens of the ABS and HIPS polymers, while in the specimen of the polymer PLA this layer showed uniformity faults. After this pretreatment was possible to perform copper electrodeposition, creating the metallic coatings on the ABS / PPy, HIPS / PPy and PLA / PPy surfaces. This metallic coating was uniform in all specimens except the one of the PLA polymer that was not sanded. The adhesion of the coating was evaluated by the adhesion test with tape and the quality of the appearance (absence of visual defects), the morphology, the uniformity, the thickness, the conductivity and the adhesion quality of the films were analyzed.

Abstract: Despite the success of osseointegrated implants, some biomechanical problems such as loosening or fracture of the abutment, crown fixation screw loosening and prosthetic instability, are common problems reported in the literature. Thus, the objective of the present study was to analyze the pullout resistance of straight and angled abutments in narrow diameter implants installed by means of friction. The specimen was composed of an implant of 3.3 mm x 11 mm fixed 2 mm above of a resin block. The abutments were fixed by friction receiving 3, 5 and 7 strikes of 0.05 J along the implant axis, and were positioned with 0 ̊, 10 ̊ and 20 ̊ of angulation. The abutments were subjected to pullout load, totalizing 10 repetitions for each test, i.e., the abutment was reinserted up to 10 times in the same implant. The results showed higher values of pullout load for the abutments with 7 strikes, and no statistical difference with 5 strikes suggesting better mechanical stability.