JOAO VICTOR DE SOUSA ARAUJO

JOAO VICTOR DE SOUSA ARAUJO

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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.
Microstructural, electrochemical and localized corrosion characterization of the AA2198-T851 alloy
2020 - ARAUJO, JOAO V. de S.; SILVA, REJANE M.P. da; DONATUS, UYIME; MACHADO, CARULINE de S.C.; COSTA, ISOLDA
In the present work, the microstructure, electrochemical behavior and localized corrosion of the AA2198-T851 Al-Cu-Li alloy were studied. The microstructure was correlated with corrosion results obtained by immersion, gel visualization and scanning electrochemical microscopy (SECM) tests. Immersion and gel visualization tests showed high kinetics of corrosion attack during the first hours of immersion. SECM analyzes by means of surface generation/tip collection (SG/TC) mode detected hydrogen evolution generated during spontaneous corrosion from severe localized corrosion (SLC) sites on the metal surface. SECM results revealed sites of intense hydrogen evolution after 2 h of immersion and increased amounts of corrosion products after 4 h of immersion. Hydrogen evolution sites detected by SECM were associated with severe localized corrosion (SLC).
Galvanic and asymmetry effects on the local electrochemical behavior of the 2098-T351 alloy welded by friction stir welding
2020 - MILAGRE, MARIANA X.; DONATUS, UYIME; MOGILI, NAGA V.; SILVA, REJANE M.P.; VIVEIROS, BARBARA V.G. de; PEREIRA, VICTOR F.; ANTUNES, RENATO A.; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; COSTA, ISOLDA
Scanning electrochemical microscopy (SECM) and scanning vibrating electrode technique (SVET) were used to investigate the electrochemical behaviour of the top surface of the 2098-T351 alloy welded by friction stir welding (FSW). The SVET technique was efficient in identifying the cathodic and anodic weld regions. The welding joint (WJ), which comprises the thermomechanically affected zone (TMAZ) and the stir zone (SZ), was cathodic relative to the heated affected zone (HAZ) and the base metal (BM). The reactivities of the welding joint at the advancing side (AS) and the retreating side (RS) were analyzed and compared using SECM technique in the competition mode by monitoring the dissolved oxygen as a redox mediator in 0.005 mol L−1 NaCl solution. The RS was more electrochemically active than the AS, and these results were correlated with the microstructural features of the welded alloy.
Effects of chloride ion concentration on the corrosion behavior of the AA2198-T8 alloy
2019 - MACHADO, CARULINE de S.C.; SILVA, REJANE M. da; ARAUJO, JOAO V. de S.; DONATUS, UYIME; MILAGRE, MARIANA X.; KLUMPP, RAFAEL E.; ROSSI, JESUALDO L.; COSTA, ISOLDA
In this work, the influence of chloride ions concentration on the corrosion behavior of the AA2198-T8 alloy was evaluated. Immersion test and electrochemical analyses were performed in sodium chloride solutions of three concentrations, 0.001 mol L-1, 0.005 mol L-1 and 0.01 mol L-1. The results showed that the AA2198-T8 alloy was susceptible to localized corrosion (LC) and to severe localized corrosion (SLC) in all conditions investigated. The electrochemical results obtained by open circuit potential measurements, cyclic voltammetry and potentiodynamic polarization curves were associated with the corroded microstructure of the alloy. Although electrochemical techniques allowed differentiating the corrosion resistance as a function of chloride concentration, the result was strongly influenced by the corroded/uncorroded area ratio related to the SLC.
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.
Exfoliation corrosion susceptibility in the zones of friction stir welded AA2098-T351
2019 - MILAGRE, MARIANA X.; DONATUS, UYIME; MACHADO, CARULINE S.C.; ARAUJO, JOAO V.S.; FERREIRA, RAPHAEL O.; SILVA, REJANE M.P.; ANTUNES, RENATO A.; COSTA, ISOLDA
In the present study, the exfoliation susceptibility of the weld zones in friction stir weldedAA2098-T351 was compared with that of the base metal (BM) according to ASTM G34 stan-dard practice. Friction stir welding (FSW) had a significant effect on the microstructure of theAl alloy tested and the susceptibility to exfoliation was strongly affected by the microstruc-ture. Different features of corrosion attack and exfoliation susceptibility were observed whenthe zones affected by FSW were tested isolated or coupled. Also, the near-surface deformedlayer had an important effect on the Al alloy susceptibility to exfoliation. These are themain findings of this work. The corrosion features were correlated with the microstructuralmodifications related to the welding process and with the electrochemical response. TheT1 phase morphology, distribution and size were critical for exfoliation susceptibility. Thestir zone (SZ) was the zone most resistant to exfoliation. However, resistance to exfoliationvaried with the temperatures reached in the heat affected zones (HAZs). The HAZ exposedto the lowest temperatures during welding, HAZ (LT), was the most susceptible to exfoli-ation, whereas the HAZ exposed to the highest temperatures, HAZ (HT), presented highresistance to exfoliation, similarly to the SZ. The ASTM-G34 practice was an effective anduseful method in identifying the different exfoliation resistances of the BM and the vari-ous zones affected by FSW. The results of this practice were supported by electrochemicalimpedance spectroscopy (EIS) tests.
Effect of surface treatments on the localized corrosion resistance of the AA2198‐T8 aluminum lithium alloy welded by FSW process
2019 - MACHADO, CARULINE de S.C.; KLUMPP, RAFAEL E.; AYUSSO, VICTOR H.; DONATUS, UYIME; MILAGRE, MARIANA X.; ARAUJO, JOAO V. de S.; MACHADO, GLAUSON A.F.; COSTA, ISOLDA
In this work, the effect of eight types of surface treatments on the corrosion resistance of friction stir welded samples of an AA2198‐T8 Al‐Cu‐Li alloy were tested and compared in an attempt to find suitable alternatives to toxic and carcinogenic hexavalent chromium treatments. All the samples were anodized and subjected to different post‐anodizing treatments. The post‐anodizing treatments were (1) hydrothermal treatment in Ce (NO3)3 6H2O solution; (2) hydrothermal treatment in Ce (NO3)3 6H2O solution with H2O2; (3) hydrothermal treatment in boiling water; (4) hexavalent chromium conversion coating; and (5) immersion in BTSE (bis‐1,2‐(triethoxysilyl) ethane. The corrosion resistance of the treated samples was evaluated by immersion tests in sodium chloride solution (0.1 mol L−1 NaCl) and electrochemical impedance spectroscopy (EIS) of the friction stir weldment. The results showed that among the alternative treatments, the Ce‐containing solutions presented the best corrosion resistance, especially when used without peroxide.
The effect of manufacturing process induced near-surface deformed layer on the corrosion behaviour of AA2198-T851 Al–Cu–Li alloy
2019 - DONATUS, UYIME; ARAUJO, JOAO V. de S.; MACHADO, CARULINE de S.C.; MOGILI, NAGA V.V.; ANTUNES, RENATO A.; COSTA, ISOLDA
The effect of the near-surface deformed layer on the corrosion behaviour of AA2198-T851 Al–Cu–Li alloy has been investigated using microscopy and electrochemical techniques. This shows that a deformed layer developed by rolling was more active but only exhibited superficial attack compared to a mechanically polished surface, which produced severe localised corrosion associated with the presence of hexagonal T1 particles. The rolled surface became increasingly corrosion resistant with time, but when coupled, galvanically enhanced severe localised corrosion sites developed on the surface over time.
Effect of unequal levels of deformation and fragmentation on the electrochemical response of friction stir welded AA2024-T3 alloy
2019 - QUEIROZ, FERNANDA M.; DONATUS, UYIME; RAMIREZ, OSCAR M.P.; ARAUJO, JOAO V. de S.; VIVEIROS, BARBARA V.G. de; LAMAKA, SVIATLANA; ZHELUDKEVICH, MIKHAIL; MASOUMI, MOHAMMAD; VIVIER, VINCENT; COSTA, ISOLDA; MELO, HERCILIO G. de
The effect of unequal levels of deformation and fragmentation on the electrochemical response of friction stir welded AA2024-T3 has been investigated using electron backscatter diffraction, scanning electron microscopy, global and localized electrochemical techniques. The friction stir welding process introduced unequal distribution and fragmentation of coarse intermetallic particles, such that more clusters of these particles were present in the thermomechanically affected zone of the weld. This resulted in a higher susceptibility to severe localized corrosion in this region when compared with the others. Results from electrochemical measurements using a microcell could not be clearly correlated with the corrosion behaviour because no significant differences were observed using these techniques. On the other hand, LEIS and SVET results were in agreement and correlated with the corrosion evolution at the surfaces of the tested samples.