MARIANA XAVIER MILAGRE

MARIANA XAVIER MILAGRE

Página do item completo

Resultados de Busca

Agora exibindo 1 - 10 de 15

Corrosion behaviour of the 2098-T351 Al–Cu–Li alloy after different surface treatments
2022 - BARBOZA, WANESSA das G.; MILAGRE, MARIANA X.; DONATUS, UYIME; MACHADO, CARULINE de S.C.; RAMIREZ, OSCAR M.P.; ARAUJO, JOAO V. de S.; SILVA, REJANE M.P. da; COSTA, ISOLDA
The effect of different surface treatments on the corrosion resistance of the AA2098 Al–Cu–Li alloy has been investigated. Surface characterization was performed using 3D optical profilometry, energy dispersive X-ray spectroscopy and scanning electron microscopy. The corrosion resistance of the 2098 alloy after the surface treatments was investigated in 0.1 mol L−1 NaCl solution by electrochemical techniques and microscopy. Corrosion results showed that the untreated and the chemically etched surfaces were more active than the mechanically abraded and mechanically polished surfaces owing to differences in the nature of the native oxides formed after the surface treatments. Corrosion rate and mode were also affected by how close the exposed surface was to the mid-thickness region of the AA2098-T351 plate relative to the actual top surface (before polishing). This is associated with the variation in the volume fraction and distribution of the T1 phase as the mid-thickness region of the AA2098-T351 plate is approached.
Corrosion behavior of the 6061 Al–Mg–Si alloy in different soils extracts
2022 - MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; MACHADO, CARULINE de S.C.; PEREIRA, MARCO S.; ANTUNES, RENATO A.; GENEZINI, FREDERICO; COSTA, ISOLDA
In this work, the corrosion behavior of the 6061 Al-alloy in different temper conditions was studied in different soil extracts using electrochemical and surface monitoring techniques. The results showed that the corrosion behavior of the 6061 alloy depends on the soil extract composition, with the highest electrochemical activities related to the soil extracts with the lowest nitrate and sulfate concentrations. The 6061-T6 condition was more susceptible to corrosion than the 6061-HCR one. The results were related to the higher amounts of MgSi particles in the 6061-T6 alloy compared to the 6061-HCR. Sulfate and nitrate ions acted as corrosion inhibitor reducing the corrosion kinetics of the 6061 alloy in solutions with high concentration of chloride ions.
Corrosion characterization of the 6061 Al–Mg–Si alloy in synthetic acid rain using neutron tomography
2022 - MILAGRE, MARIANA X.; PEREIRA, MARCO S.; GOMES, ANTONIO A.; SCAPIN, MARCOS; FRANCO, MARGARETH; YOKAICHIYA, FABIANO; GENEZINI, FREDERICO; COSTA, ISOLDA
Neutron tomography has gained increasing importance as an imaging technique for materials characterization. In general, neutron beams are able to show microstructure features of hydrogenous materials, even enfolded with thick metal layers. In the present paper, neutron tomography and observation of cross section images were successfully applied to investigate the corrosion features of the 6061 Al–Mg–Si alloy. The results showed good agreement between neutron 3D tomography and the cross section images obtained in the high attenuation areas of the samples, whereas significant differences in depth of corrosion penetration were obtained between the results from Neutron Tomography and 3D optical profilometry.
TSA anodising voltage effects on the near-surface coarse intermetallic particles in the AA2024-T3 and AA2198-T8 alloys
2022 - ARAUJO, JOAO V. de S.; MILAGRE, MARIANA X.; KLUMPP, RAFAEL E.; AYUSSO, VICTOR H.; DONATUS, UYIME; COSTA, ISOLDA
In this study, the behaviour of the micrometric particles of the AA2198-T8 alloy during anodising at various voltages and the effect of anodising voltage on the anodised surface morphology have been investigated in a tartaric-sulfuric acid anodising solution. The results were compared with that of the AA2024-T3 alloy. For the AA2198-T8 alloy, partial dissolution of these particles occurred at 0, 3 and 4 V. Besides, for potentials above 5 V, there is a preferential dissolution of the intermetallic particles. For the AA2024-T3 alloy, the results indicated a total dissolution of the micrometric particles at 0 V and a partial dissolution at 3 V, whereas above 4 V total dissolution occurred. Between 1 and 2 V, no dissolution was observed for both alloys. The preferential dissolution of the micrometric particles resulted in defects in the anodic film and cavities on the anodised surfaces.
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.
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.
Exfoliation and intergranular corrosion resistance of the 2198 Al–Cu–Li alloy with different thermomechanical treatments
2020 - ARAUJO, JOAO V. de S.; MILAGRE, MARIANA X.; FERREIRA, RAPHAEL O.; MACHADO, CARULINE de S.C.; BUGARIN, ALINE de F.S.; MACHADO, IZABEL F.; COSTA, ISOLDA
In this study, the resistance to exfoliation and intergranular corrosion (IGC) of the 2198 Al–Cu–Li alloy submitted to different thermomechanical treatments (T3, T8, and T851) was investigated. The tests were carried out following the standard practices, ASTM G34‐18 and ASTM G110‐15, respectively. All the tested alloys showed susceptibility to exfoliation and some alloys showed susceptibility to IGC, but the artificially aged alloys presented a higher tendency to exfoliation. The extensive hydrogen evolution reaction (HER) was observed on the surfaces of artificially aged alloys when immersed in the EXCO solution. The HER resulted in an increase in solution pH with the time of immersion. Also, the weight losses related to the artificially aged alloys were higher than that of the naturally aged ones. The T8 treatment was the only condition that resulted in susceptibility to both, intergranular and transgranular corrosion, whereas the T851 treatment did not show IGC susceptibility, only transgranular corrosion. Finally, the 2198‐T3 condition showed the highest corrosion resistance among the thermomechanical treatments tested. The results of the 2198 alloy subjected to various treatments were compared with that of the 2024‐T3 alloy. This last alloy showed higher resistance to exfoliation and IGC as compared with the 2198 alloy.
Galvanic coupling effects on the corrosion behavior of the 6061 aluminum alloy used in research nuclear reactors
2020 - MILAGRE, MARIANA X.; DONATUS, UYIME; SILVA, REJANE M.P.; BETANCOR-ABREU, ABENCHARA M.; RAMIREZ, OSCAR M.P.; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; SOUTO, RICARDO M.; COSTA, ISOLDA
The 6061 alloy is used in different thermomechanical conditions in research nuclear reactors. Nuclear fuel plates are manufactured by the picture frame technique (PFT) and the 6061 alloy is used as cladding for the nuclear fuel “sandwiches”. After the PFT process, these nuclear plates are placed in a case made of 6061-T6 alloy. In this work, the galvanic effects of coupling the 6061 alloy in the T6 and PFT temper conditions were investigated in different chloride-containing solutions. The results showed that galvanic coupling was favored between the PFT and 6061-T6 alloy. A potential difference of about 50 mV was observed between the temper conditions. This was attributed to differences in β’’ phase density between the two conditions (T6 and PFT) which was indicated by microhardness results. The 6061 alloy in the PFT condition was cathodic in relation to the T6 one. Results from conventional electrochemical techniques were in agreement with the local measurements. Local electrochemical techniques such as the SVET, SECM and LEIS were useful in characterizing the electrochemical behavior of the galvanically coupled alloys.
Effects of Picture Frame Technique (PFT) on the corrosion behavior of 6061 aluminum alloy
2020 - MILAGRE, MARIANA X.; DONATUS, UYIME; MOGILI, NAGA V.; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; KLUMPP, RAFAEL E.; FERNANDES, STELA M.C.; SOUZA, JOSE A.B. de; COSTA, ISOLDA
The 6061 Al–Mg–Si alloy is used in nuclear fuel plates of nuclear research reactors which are fed with fuel in plate shapes. The production of these plates is based on the picture frame technique (PFT). The picture frame technique (PFT) is a manufacturing process for the fabrication of nuclear fuel plates where the nuclear fuel is encapsulated by Al alloy plates and thermomechanically processed to generate a set with reduced thickness. The effects of PFT on the corrosion resistance of the 6061 aluminum alloy were evaluated in this study by immersion and electrochemical tests in 0.005 mol L−1 NaCl solution. The results showed that the PFT fabrication process increases the corrosion resistance of the 6061 alloy in relation to the conventional 6061-T6, due phase dissolution and lower content of β’’ phase. Also, corrosion propagation gradually changes, with an increasing number of processing steps, from intergranular to intragranular corrosion attack.
Correlating the modes of corrosion with microstructure in the friction stir welded AA2198-T8 alloy in aqueous hydrogen peroxide-chloride medium
2019 - MACHADO, CARULINE de S.C.; DONATUS, UYIME; MILAGRE, MARIANA X.; MOGILI, NAGA V.V.; GIORJÃO, RAFAEL A.R.; KLUMPP, RAFAEL E.; ARAUJO, JOAO V. de S.; FERREIRA, RAPHAEL O.; COSTA, ISOLDA
In this study, different types of localized corrosion in the friction stir welding (FSW) zones of an AA2198-T8 when the alloy is subjected to a corrosion test in a hydrogen peroxide–chloride solution (according to ASTM G110 standard) has been investigated. The corrosion modes were correlated with microstructure, especially with respect to the T1 phase and coarse Al-Cu-Fe phase distribution across the weldment. Simulated thermal profile and microhardness measurements were used to establish the variations in T1 phase distribution. Two types of corrosion were observed in the FSW zones: intense pitting and intergranular corrosion—type I; and the formation of cavities and trenches—type II. Type I is associated with the T1 phase while type II is associated with Al-Cu-Fe coarse intermetallics. Both types were found on the base metal (BM) and heat affected zone, but the type I reduced in the latter toward the stir zone (SZ). The SZ/thermomechanically affected zone (TMAZ) exhibited only type II. Also, Cu enrichment was observed around the type II sites in the SZ/TMAZ. Furthermore, an inverse correlation between microhardness and corrosion resistance which was related to T1 phase concentration in the different zones was also observed. Moreover, the SZ and BM were isolated and evaluated by an immersion test and electrochemical analysis using the ASTM G110 test solution. The results indicated galvanic coupling effects, as the SZ was strongly attacked when exposed separately compared to when it was coupled with the other zones.