CARULINE DE SOUZA CARVALHO MACHADO

CARULINE DE SOUZA CARVALHO MACHADO

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Investigação da atividade eletroquímica de liga Al-Cu-Li após processo de soldagem por fricção e mistura
2023 - SILVA, REJANE M.P. da; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; RAMIREZ, OSCAR M.P.; MACHADO, CARULINE de S.C.; ANTUNES, RENATO A.; COSTA, ISOLDA
In this work, the local electrochemical activity of the zones coupled by Friction Stir Welding (FSW) of an Al-Cu-Li alloy was studied and the results were correlated to the microstructural characteristics of each zone. Electrochemical studies were carried out in the zones affected by welding using cyclic voltammetry (CV) and scanning electrochemical techniques (namely, SECM - Scanning Electrochemical Microscopy and LEIS – Local electrochemical impedance spectroscopy). The results showed that the welding joint (WJ) is predominantly cathodic relatively to the heat affected zones (HAZ). The HAZ was always anodic and showed the highest electrochemical activities among the tested ones. The high electrochemical activity of the HAZ was associated with the effect of galvanic coupling between the cathodic region (WJ) and the anodic region (HAZ). In addition, the advancing side (AS) presented increased electrochemical activity compared to the retreating one (RS).
Estudo da resistência à corrosão dos materiais envolvidos no sistema de armazenamento de combustível nuclear queimado (CNQ) do reator IEA-R1
2022 - PIOVESAN, JOAO V.R.; GABBARDO, ALINE D.; MACHADO, CARULINE de S.C.; COSTA, ISOLDA
A homemade electrochemical hanging droplet cell to evaluate the corrosion resistance of friction stir weld zones of the AA2198-T8 Al-Cu-Li alloy
2021 - MACHADO, CARULINE de S.C.; HERNANDEZ, JOSE W.C.; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; DONATUS, UYIME; COSTA, ISOLDA
In this study, the corrosion resistance of the different zones of the AA2198-T8 alloy welded using friction stir welding (FSW) was investigated by immersion and electrochemical tests during exposure to 0.005 mol L-1 NaCl solution. After immersion tests, the welding zones were classified in two groups, according to their severe localized corrosion (SLC) morphology. Zones exposed to higher temperatures during welding presented intergranular attack, whereas those exposed to lower temperatures presented intragranular attack. Electrochemical measurements performed employing a homemade hanging droplet cell revealed potential galvanic coupling between the two groups. The base metal (BM) presented the most anodic potentials. The open circuit potential (OCP) increased from BM towards the stir zone (SZ). The results obtained by the hanging droplet cell were reproducible and coherent with the classification of the zones in the two proposed groups. The homemade electrochemical hanging droplet cell proved a very reliable tool to investigate the electrochemical behavior of the FSWed zones in Al-Cu-Li alloys.
A cerium-based nanocoating for corrosion protection of clad on AA 2024-T3 alloy
2021 - KLUMPP, RAFAEL E.; MACHADO, CARULINE de S.C.; ARAUJO, JOAO V. de S.; ANTUNES, RENATO A.; MAGNANI, MARINA; COSTA, ISOLDA
Aluminum alloys are susceptible to localized corrosion resulting in a major risk for aircrafts due to the extensively use of this material in their structures. Therefore, the surface protection of these alloys against corrosion is fundamental. In this work, an eco-friendly surface pretreatment cerium based for corrosion protection alternatively to chromate based ones was developed and applied on the clad of the 2024-T3 aluminum alloy. The corrosion resistance of the modified surface was evaluated by electrochemical impedance spectroscopy, polarization and Scanning Vibrating Electrode Techniques The results obtained were compared to a chromium based conventional treatment and revealed that the coating layer resulting from the tested treatment resulted in a film composed by spherical nodular nanostructures of cerium that improved the corrosion resistance of the alloy studied and it was comparable to the effect of treatment with hexavalent chromium showing it is an promising alternative to replacing treatments based on environmental harmful treatments.
Compreendendo os mecanismos de corrosão de ligas de Al-Cu-Li
2022 - ARAUJO, JOAO V. de S.; SILVA, REJANE M.P. da; VIVEIROS, BARBARA V.; MILAGRE, MARIANA X.; MACHADO, CARULINE de S.C.; COSTA, ISOLDA
In this study, the corrosion mechanism of an Al-Cu-Li alloy manufactured by two different treatment routes (T3 and T851) was evaluated by immersion and electrochemical tests in solutions containing chloride ions (Cl-). For both alloys, the formation of cavities on the surface was associated with micrometer-sized intermetallics (IM’s), however, in addition to this attack, the alloy submitted to T851 treatment also presented an attack called severe localized corrosion (SLC), caused by the preferential attack to the nanometric T1 (Al2CuLi) phase. The electrochemical concepts involved in these two types of attacks were discussed. During the IM’s corrosive process, whereas the O2 reduction occurred over the IM’s, the Al dissolution is favored around the particle, forming trenching and cavities (with 2 and 6 mm of depth). On the other hand, the mechanism associated with the SLC is related to the formation of a differential aeration cell followed by the evolution of H2, with greater depth of attack penetration (8 and 35 mm). Additionally, by the use of the Scanning Vibrating Electrode Technique (SVET), it was concluded that the higher anodic currents observed for the T851 temper were related to the relation between the anodic area (Aa) and the cathodic area (Ac).
Corrosion resistance of precipitation-hardened Al alloys
2021 - DONATUS, UYIME; BODUNRIN, MICHAEL O.; OLAYINKA, AYOTUNDE; MILAGRE, MARIANA X.; OLOYEDE, OLAMILEKAN R.; ARIBO, SUNDAY; ARAUJO, JOAO V. de S.; MACHADO, CARULINE de S.C.; COSTA, ISOLDA
The corrosion resistance of conventional (AA2024-T3, AA6082-T6 and AA7050-T7451) and the new generation (AA2050-T84, AA2098-T351, AA2198-T8, and AA2198-T851) precipitation-hardened alloys has been studied and compared using electrochemical and non-electrochemical approaches. The AA6082-T6 was the most resistant alloy followed by the new generation Al-Cu-Li alloys, except the AA2050-T84. All the alloys exhibited pseudo-passivity, except for the AA2024-T3 alloy which presented the highest number of pitting sites per cm2 and also exhibited the most insidious form of corrosion amongst the alloys tested. However, the alloy with the highest corrosion depth was the AA2050-T84 alloy followed by the AA2024-T3 and AA7050-T7451 alloys. Intergranular corrosion was associated with rapid rates of penetration. In addition to the microstructural features of the alloys before corrosion, the modes of localized corrosion in the alloys were also influenced by evolving microstructural features (such as re-deposited Cu) during corrosion.
Influence of chloride ions concentration on the development of severe localised corrosion and its effects on the electrochemical response of the 2198-T8 alloy
2021 - MACHADO, CARULINE de S.C.; SILVA, REJANE M.P. da; ARAUJO, JOAO V. de S.; MILAGRE, MARIANA X.; DONATUS, UYIME; VIVEIROS, BARBARA V.G. de; KLUMPP, RAFAEL E.; COSTA, ISOLDA
The development of severe localised corrosion (SLC) on the 2198-T8 alloy was investigated in solutions of various NaCl concentrations (0.001, 0.005 and 0.01 mol L−1). Immersion tests, optical profilometry, conventional and local electrochemical analyses were performed to evaluate the corrosion behaviour of the alloy. Immersion tests showed that the alloy is susceptible to SLC in all conditions, although the pits sizes were dependent on the solution concentration. The largest anodic areas, corresponding to SLC sites, were observed for the sample immersed in 0.001 mol L−1 NaCl, whereas pits with similar sizes were observed for the samples immersed in solutions with 0.005 and 0.01 mol L−1 of NaCl. Moreover, the maximum depth of attack was observed for the sample immersed in 0.001 mol L−1 NaCl. These results were in agreement with the scanning ionselective electrode technique (SIET) maps which showed stronger acidification on the sample exposed to 0.001 mol L−1 NaCl solution.
How microstructure affects localized corrosion resistance of stir zone of the AA2198-T8 alloy after friction stir welding
2021 - MACHADO, CARULINE de S.C.; DONATUS, UYIME; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; VIVEIROS, BARBARA V.G. de; KLUMPP, RAFAEL E.; PEREIRA, VICTOR F.; COSTA, ISOLDA
In this study, the microstructure and corrosion resistance of the stir zone (SZ) of the AA2198-T8 Al-Cu-Li alloy welded by friction stir welding (FSW) were investigated by microscopy, immersion tests and electrochemical techniques such as measurements of open circuit potential variation with time, and scanning vibrating electrode technique (SVET) measurements. A low chloride-containing solution (0.005 mol L−1 NaCl) was employed in the corrosion studies and severe localized corrosion (SLC) was observed in the SZ related to intergranular attack. The results were compared to those of the non-affected areas by FSW, also known as base metal (BM). In the BM, SLC was found and the type of attack related to it was intragranular. In both zones, BM and SZ, SLC was due to precipitates of high electrochemical activity, specifically T1 (Al2CuLi) phase in the BM, whereas TB (Al7Cu4Li) / T2 (Al6CuLi3) in the SZ. Scanning vibrating electrode technique (SVET) analysis was very useful in the study of SLC in the AA2198-T8 alloy showing the development of high anodic current densities at the mouth of the SLC sites.
Corrosion protection of the AA2198-T8 alloy by environmentally friendly organic-inorganic sol-gel coating based on bis-1,2-(triethoxysilyl) ethane
2021 - KLUMPP, RAFAEL E.; DONATUS, UYIME; SILVA, REJANE M.P. da; ANTUNES, RENATO A.; MACHADO, CARULINE de S.C.; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; VIVEIROS, BARBARA V.G. de; COSTA, ISOLDA
In this work, a surface coating composed of organic‐inorganic hybrid sol‐gel based on bis‐1,2‐(triethoxysilyl) (BTSE) ethane was applied on AA2198‐T8 samples, and its effect on corrosion resistance was investigated and compared with that of a chromate layer formed in a solution with hexavalent chromium ions. The corrosion resistance of BTSE coated samples was evaluated by immersion tests in sodium chloride solution (0.005 mol/L NaCl) and monitored by global electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and local electrochemical techniques such as scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM). The formed coating layers were characterized by X‐ray photoelectron spectroscopy (XPS). The results pointed out that the BTSE is an effective alternative coating for corrosion protection of new generation Al‐Cu‐Li alloys and could replace chromates obtained in toxic and carcinogenic CrVI containing solutions leading to improved corrosion protection.
Hybrid composites with glass fiber and natural fibers of sisal, coir, and luffa sponge
2021 - SILVA, ROSANA V. da; VOLTZ, HIURY; ITMAN FILHO, ANDRE; MILAGRE, MARIANA X.; MACHADO, CARULINE de S.C.
Hybrid composites with synthetic and natural fibers are a good choice in the field of composites, as they combine the good mechanical performance of synthetic fibers with the advantages of natural fibers. In this work, polymeric hybrid composites associating glass fiber and natural fibers were developed. Three hybrid composites were developed: sisal/ glass, coir/glass and Luffa/glass. The composites are five-layer laminate, three layers of E-glass interspersed with two layers of natural fibers that can be sisal, coir, or Luffa sponge (Luffa Cylindrica). In addition to hybrid composites, a five-layer fiberglass composite was also manufactured. The composites were manufactured by compression molding technique using orthophthalic polyester resin as matrix. Tensile and flexural tests were performed to characterize the composites. Considering the three hybrid composites, the best behavior was observed for the sisal/glass composite, being a potential replacement for fiberglass. The order of performance was the same in the tensile and flexural tests, sisal/glass, coir/glass, and luffa/glass, in this order. In the specimen’s fracture analysis, for both tests, it was observed that the fracture was quite located with no damage in regions far from the fracture. This behavior indicates good adhesion between the layers of natural and synthetic fibers, despite the discrepancy of their properties.