MARIANA XAVIER MILAGRE
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Resumo IPEN-doc 28449 Microelectrochemical evaluation of severe localized corrosion sites developing on third-generation aluminium alloys2021 - IZQUIERDO, J.; SILVA, R.M.P. da; MILAGRE, M.X.; COSTA, I.; BETANCOR-ABREU, A.M.; SOUTO, R.M.Third-generation aluminium-copper-lithium alloys exhibit attractive mechanical properties, in particular light-weight and significant strength. However, the developed microstructure often results in severe localized corrosion (SLC) sites with fast in-depth pit propagation accompanied by H2 evolution.1 Such phenomena stem from a strong galvanic coupling, mainly established between Fe- and Cu-rich particles and the surrounding matrix. As a result, strong concentration and pH gradients develop throughout the aluminium surface, determining the local breakdown of the passive regime eventually provided by aluminium oxides and corrosion products. Understanding the development of such distributions is key to outline appropriate strategies for the prevention of fast degradation and materials failure. Scanning Electrochemical Microscopy (SECM) and Scanning Vibrating Electrode Technique (SVET) are capable of providing local information on the distribution of active sites and the presence of reactive chemical species. SVET has previously demonstrated the formation of gas bubbles ascribed to hydrogen evolution (i.e., electro-reduction process) at the anodically-activated sites,2,3; whereas local hydrogen production, oxygen consumption and pH changes are readily accessible using SECM, although with some limitations with regards to the detection of evolving gas.4 The present contribution reports recent advances in the investigation of local degradation phenomena occurring at the surface of Al-Cu-Li alloy AA-2098, as bare material and after friction stir welding. Oxygen consumption over nobler particles acting as cathodic sites, and SLC accompanied with strong acidification and H2 production at the local anodes were observed. The determined pH and concentration gradients allow to progress in the knowledge of the mechanistic aspects involved in the degradation processes on these materials.Resumo IPEN-doc 26824 Influence of surface finishing on the electrochemical activity of the 2098-T351 aluminum alloy2019 - SILVA, REJANE; MILAGRE, MARIANA; OLIVEIRA, LEANDRO; ANTUNES, RENATO; DONATUS, UYIME; COSTA, ISOLDAIn this work, scanning electrochemical microscopy (SECM) measurements were employed to characterize the electrochemical activities of polished and as-received surfaces of the 2098-T351 aluminum alloy (AA2098-T351). The effects of the near surface deformed layer (NSDL) and its removal by polishing on the electrochemical activities of the alloy surface were evaluated and compared by the use of different modes of SECM. Confocal Laser Scanning Microscopy (CLSM) and energy dispersive X-ray spectroscopy (EDS) were also employed to characterize the morphology of the surfaces. The surface chemistry was analyzed by X-ray Photoelectron Spectroscopy (XPS). The generation/tip collection (SG/TC) and competition modes of the SECM were used to study hydrogen gas (H2) evolution and oxygen reduction reactions, respectively. H2 evolution and oxygen reduction were more pronounced on the polished surface compared to the asreceived surface that revealed lower electrochemical activities showing that either the NSDL largely decreased the local electrochemical activities at the AA2098-T351 surface.Resumo IPEN-doc 25338 Application of scanning electrochemical microscopy (SECM) for local characterization of AA2098-T351 surface in different conditions2018 - SILVA, R.M.P.; MILAGRE, M.X.; COSTA, I.; OLIVEIRA, L.A. deAluminum alloys are commonly used in automotive and aerospace applications because of their good mechanical properties and low density. The aluminum-lithium (Al-Li) alloys are a class of Al-alloys which have some superior properties, such as lower densities than conventional ones and, for this reason, used as structural components in aircrafts. The addition of lithium aims to reduce density of the material with gains in the mechanical properties and in the specific modules, which is important for the aerostructures. However, the addition of this element usually increases localized corrosion susceptibility. The scanning electrochemical microscopy (SECM) technique can provide a good understanding about the corrosion behavior and the local reactions of this class of materials. In this work, different modes of SECM measurements were employed to characterize the AA2098-T351 surface in various conditions. The surface generation/tip collection (SG/TC) mode and competition mode were employed to study the hydrogen gas (H2) evolution and oxygen reduction, respectively, in the AA2098-T351 surface in the conditions: polished and unpolished. It was found that the main domains of H2 evolution and oxygen reduction are associated with the alloy surface in the polished condition.The feedback mode of SECM was employed to characterize the electrochemical activity of the surface after immersion in a solution containing ions chloride, in order to verify the influence of the oxide layer formation over the surface in the active/passive domains due the corrosion process. The previously attacked surface revealed a much lower electrochemical activity compared with the surface in the polished condition due to the protective character of the oxide formed during immersion test.