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Kharitonov, D., Sommertune, J., Örnek, C., Ryl, J., Kurilo, I., Claesson, P. M. & Pan, J. (2019). Corrosion inhibition of aluminium alloy AA6063-T5 by vanadates: Local surface chemical events elucidated by confocal Raman micro-spectroscopy. Corrosion Science, 148, 237-250
Open this publication in new window or tab >>Corrosion inhibition of aluminium alloy AA6063-T5 by vanadates: Local surface chemical events elucidated by confocal Raman micro-spectroscopy
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2019 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 148, p. 237-250Article in journal (Refereed) Published
Abstract [en]

Chemical interactions between aqueous vanadium species and aluminium alloy AA6063-T5 were investigated in vanadate-containing NaCl solutions. Confocal Raman and X-ray photoelectron spectroscopy experiments were utilised to gain insight into the mechanism of corrosion inhibition by vanadates. A greenish-grey coloured surface layer, consisting of V+4 and V+5 polymerized species, was seen to form on the alloy surface, especially on top of cathodic micrometre-sized IMPs, whereby suppressing oxygen reduction kinetics. The results suggest a two-step mechanism of corrosion inhibition in which V+5 species are first reduced to V+4 or V+3 species above cathodic IMPs, and then oxidized to mixed-valence V+5/V+4 polymerized compounds. 

Keywords
A. Alloy, A. Aluminium, B. Raman spectroscopy, B. SEM, B. XPS, C. Vanadate inhibitor, Corrosion inhibitors, Electrolytic reduction, Sodium alloys, Sodium chloride, Transition metal compounds, Vanadium alloys, X ray photoelectron spectroscopy, Chemical interactions, Corrosion inhibition, Local surfaces, Mechanism of corrosion, Oxygen reduction kinetics, Two-step mechanisms, Vanadium species, Aluminum corrosion
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-37038 (URN)10.1016/j.corsci.2018.12.011 (DOI)2-s2.0-85059158841 (Scopus ID)
Note

 Funding details: Belarusian State University, BSU; Funding details: IP2015067574; Funding details: Ministry of Education of the Republic of Belarus, 20161135; Funding details: Stiftelsen för Strategisk Forskning; Funding details: Kungliga Tekniska Högskolan, KTH; Funding details: Sjögren’s Syndrome Foundation, RMA11-0090; Funding details: Knut och Alice Wallenbergs Stiftelse;

Available from: 2019-01-17 Created: 2019-01-17 Last updated: 2019-06-28Bibliographically approved
Kharitonov, D. S., Örnek, C., Claesson, P. M., Sommertune, J., Zharskii, I. M., Kurilo, I. I. & Pan, J. (2018). Corrosion Inhibition of Aluminum Alloy AA6063-T5 by Vanadates: Microstructure Characterization and Corrosion Analysis. Journal of the Electrochemical Society, 5(3), C116-C126
Open this publication in new window or tab >>Corrosion Inhibition of Aluminum Alloy AA6063-T5 by Vanadates: Microstructure Characterization and Corrosion Analysis
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2018 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 5, no 3, p. C116-C126Article in journal (Refereed) Published
Abstract [en]

Corrosion inhibition of aluminum alloy AA6063-T5 by vanadates (NaVO3) in 0.05 M NaCl solution has been investigated by electrochemical and weight loss measurements, and associated with microstructure and Volta potential data. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy analyses confirmed the presence of micrometer-sized Fe-rich Al4.01MnSi0.74, Al1.69Mg4Zn2.31, and FeAl3intermetallic phases (IMPs) and nanometer-sized CuAl2, ZnAl2, and Mg2Si precipitates in the microstructure. Scanning Kelvin probe force microscopy measurements showed Volta potential differences of up to 600 mV between the microstructure constituents indicating a high susceptibility to micro-galvanic corrosion, with interphase boundary regions exhibiting the highest propensity to corrosion. Most IMPs had cathodic character whereas some nanometer-sized Mg-rich particles exhibited anodic nature, with large Volta potential gradients within interphase regions of large cathodic particles. Electrochemical potentiodynamic polarization measurements indicated that the vanadates provided mixed corrosion inhibition effects, mitigating both oxygen reduction, occurring on cathodic IMPs, and anodic metal dissolution reaction, occurring on anodic sites, such as Mg2Si and interphase boundary regions. Electrochemical measurements indicated that the sodium metavanadate inhibitor blocks active metal dissolution, giving high inhibition efficiency (>95%) during the initial exposure, whereas long-term weight loss measurements showed that the efficacy decreases after prolonged exposure.

Keywords
Aluminum Alloy AA6063-T5 Sodium Metavanadate (NaVO3) Corrosion Inhibition Microstructure Characterization Scanning Kelvin Probe Force Microscopy (SKPFM) Electrochemical Impedance Spectroscopy (EIS)
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-34071 (URN)10.1149/2.0341803jes (DOI)2-s2.0-85044021625 (Scopus ID)
Available from: 2018-07-06 Created: 2018-07-06 Last updated: 2019-06-17Bibliographically approved
Örnek, C., Reccagni, P., Kivisäkk, U., Bettini, E., Engelberg, D. L. & Pan, J. (2018). Hydrogen embrittlement of super duplex stainless steel – Towards understanding the effects of microstructure and strain. International journal of hydrogen energy, 43(27), 12543-12555
Open this publication in new window or tab >>Hydrogen embrittlement of super duplex stainless steel – Towards understanding the effects of microstructure and strain
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2018 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 43, no 27, p. 12543-12555Article in journal (Refereed) Published
Abstract [en]

The effects of austenite spacing, hydrogen charging, and applied tensile strain on the local Volta potential evolution and micro-deformation behaviour of grade 2507 (UNS S32750) super duplex stainless steel were studied. A novel in-situ methodological approach using Digital Image Correlation (DIC) and Scanning Kelvin Probe Force Microscopy (SKPFM) was employed. The microstructure with small austenite spacing showed load partitioning of tensile micro-strains to the austenite during elastic loading, with the ferrite then taking up most tensile strain at large plastic deformation. The opposite trend was seen when the microstructure was pre-charged with hydrogen, with more intense strain localisation formed due to local hydrogen hardening. The hydrogen-charged microstructure with large austenite spacing showed a contrasting micro-mechanical response, resulting in heterogeneous strain localisation with high strain intensities in both phases in the elastic regime. The austenite was hydrogen-hardened, whereas the ferrite became more strain-hardened. SKPFM measured Volta potentials revealed the development of local cathodic sites in the ferrite associated with hydrogen damage (blister), with anodic sites related to trapped hydrogen and/or micro voids in the microstructure with small austenite spacing. Discrete cathodic sites with large Volta potential variations across the ferrite were seen in the coarse-grained microstructure, indicating enhanced susceptibility to micro-galvanic activity. Microstructures with large austenite spacing were more susceptible to hydrogen embrittlement, related to the development of tensile strains in the ferrite.

Keywords
Austenite spacing, Hydrogen embrittlement, Load partitioning, Super duplex stainless steel, Volta potential, Austenite, Ferrite, Hydrogen, Microstructure, Stainless steel, Strain hardening, D. digital image correlation (DIC), Heterogeneous strain, Large plastic deformation, Methodological approach, Scanning Kelvin probe force microscopy, Volta potential variation, Tensile strain
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-34295 (URN)10.1016/j.ijhydene.2018.05.028 (DOI)2-s2.0-85047740574 (Scopus ID)
Note

Export Date: 30 July 2018; Article; CODEN: IJHED; Correspondence Address: Örnek, C.Drottning Kristinas Väg 51, Sweden; email: ornek@kth.se

Available from: 2018-08-06 Created: 2018-08-06 Last updated: 2019-06-17Bibliographically approved
Örnek, C., Långberg, M., Evertsson, J., Harlow, G., Linpé, W., Rullik, L., . . . Pan, J. (2018). In-situ synchrotron GIXRD study of passive film evolution on duplex stainless steel in corrosive environment. Corrosion Science, 141, 18-21
Open this publication in new window or tab >>In-situ synchrotron GIXRD study of passive film evolution on duplex stainless steel in corrosive environment
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2018 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 141, p. 18-21Article in journal (Refereed) Published
Abstract [en]

This paper presents new findings about the passive film formed on super duplex stainless steel in ambient air and corrosive environments, studied by synchrotron grazing-incidence X-ray diffraction (GIXRD). The passive film, formed in air, was seen to be a nano-crystalline mixed-oxide. Electrochemical polarisation to the passive region in aqueous 1 M NaCl at room temperature resulted in an increase of the passive film thickness, preferential dissolution of Fe, and partial loss of crystallinity. After termination of polarization to the transpassive regime, reformation of the mixed-oxides was observed, showing a thicker, semi-crystalline, and more defective nature (more vacancies) with further new oxides/hydroxides.

Keywords
De-alloying, Duplex stainless steel, Grazing-incidence X-ray diffraction (GIXRD), Oxide film, Passivity, Selective dissolution, Crystalline materials, Dealloying, Dissolution, Oxide films, Polarization, Sodium chloride, Steel corrosion, X ray diffraction, Corrosive environment, Electrochemical polarisation, Grazing-incidence X-ray diffraction, Preferential dissolution, Super duplex stainless steel, Stainless steel
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-34501 (URN)10.1016/j.corsci.2018.06.040 (DOI)2-s2.0-85049421217 (Scopus ID)
Note

 Funding details: 2015-04490, VR, Vetenskapsrådet;

Funding details: 2015-06092, VR, Vetenskapsrådet;

Available from: 2018-08-09 Created: 2018-08-09 Last updated: 2019-06-17Bibliographically approved
A. Hosseini, V., Karlsson, L., Örnek, C., Reccagni, P., Wessman, S. & Engelberg, D. (2018). Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method. Materials Characterization, 139, 390-400
Open this publication in new window or tab >>Microstructure and functionality of a uniquely graded super duplex stainless steel designed by a novel arc heat treatment method
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2018 (English)In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 139, p. 390-400Article in journal (Refereed) Published
Abstract [en]

A novel arc heat treatment technique was applied to design a uniquely graded super duplex stainless steel (SDSS), by subjecting a single sample to a steady state temperature gradient for 10 h. A new experimental approach was used to map precipitation in microstructure, covering aging temperatures of up to 1430 °C. The microstructure was characterized and functionality was evaluated via hardness mapping. Nitrogen depletion adjacent to the fusion boundary depressed the upper temperature limit for austenite formation and influenced the phase balance above 980 °C. Austenite/ferrite boundaries deviating from Kurdjumov–Sachs orientation relationship (OR) were preferred locations for precipitation of σ at 630–1000 °C, χ at 560–1000 °C, Cr2N at 600–900 °C and R between 550 °C and 700 °C. Precipitate morphology changed with decreasing temperature; from blocky to coral-shaped for σ, from discrete blocky to elongated particles for χ, and from polygonal to disc-shaped for R. Thermodynamic calculations of phase equilibria largely agreed with observations above 750 °C when considering nitrogen loss. Formation of intermetallic phases and 475 °C-embrittlement resulted in increased hardness. A schematic diagram, correlating information about phase contents, morphologies and hardness, as a function of exposure temperature, is introduced for evaluation of functionality of microstructures. 

Keywords
475 °C-embrittlement, Chi phase, Functionally graded microstructure, Nitrogen loss, R-phase, Sigma phase, Austenite, Chromium compounds, Cold rolling, Embrittlement, Hardness, Heat treatment, Microstructure, Nitrogen, Nitrogen compounds, Phase equilibria, Schematic diagrams, Stainless steel, Functionally graded microstructures, R phase, Temperature
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-33894 (URN)10.1016/j.matchar.2018.03.024 (DOI)2-s2.0-85044113030 (Scopus ID)
Note

 Funding details: VINNOVA; Funding details: 2016-02834; Funding details: 20140130; Funding text: The financial support from the KK-foundation for the research school SiCoMaP ( 20140130 ) and the DUWELTOOL project ( 2016-02834 ) funded by Vinnova is acknowledged.

Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2019-06-17Bibliographically approved
Örnek, C., Liu, M., Pan, J., Jin, Y. & Leygraf, C. (2018). Volta Potential Evolution of Intermetallics in Aluminum Alloy Microstructure Under Thin Aqueous Adlayers: A combined DFT and Experimental Study. Topics in catalysis, 61(9-11), 1169-1182
Open this publication in new window or tab >>Volta Potential Evolution of Intermetallics in Aluminum Alloy Microstructure Under Thin Aqueous Adlayers: A combined DFT and Experimental Study
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2018 (English)In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028, Vol. 61, no 9-11, p. 1169-1182Article in journal (Refereed) Published
Abstract [en]

In this work, first-principle density functional theory (DFT) was used to calculate the work function and Volta potential differences between aluminum alloy matrix and two intermetallic phases (Mg2Si and Al2Cu) with varying surface terminations as a function of adhering monolayers (ML) of water. The calculated data were compared with experimental local Volta potential data obtained by the scanning Kelvin probe force microscopy (SKPFM) on a commercial aluminum alloy AA6063-T5 in atmospheric environments with varying relative humidity (RH). The calculations suggest that the surface termination has a major effect on the magnitude and polarity of the Volta potential of both intermetallic phases (IMP’s). The Volta potential difference between the IMP’s and the aluminum matrix decreases when the surface is gradually covered by water molecules, and may further change as a function of adhering ML’s of water. This can lead to nobility inversions of the IMP’s relative to the aluminum matrix. The measured Volta potential difference between both IMP’s and their neighboring matrix is dependent on RH. Natural oxidation in ambient indoor air for 2 months led to a nobility inversion of the IMP’s with respect to the aluminum matrix, with the intermetallics showing anodic nature already in dry condition. The anodic nature of Al2Cu remained with the introduction of RH, whereas Mg2Si became cathodic at high RH, presumably due to de-alloying of Mg and oxide dissolution. The DFT calculations predicted an anodic character of both IMP’s in reference to the oxidized aluminum matrix, being in good agreement with the SKPFM data. The DFT and SKPFM data were discussed in light of understanding localized corrosion of aluminum alloys under conditions akin to atmospheric exposure. 

Keywords
Aluminum, Aqueous adlayer, DFT, Intermetallics, SKPFM, Volta potential, Aluminum corrosion, Anodic oxidation, Atmospheric corrosion, Atmospheric humidity, Binary alloys, Copper alloys, Dealloying, Density functional theory, Localized corrosion, Magnesium compounds, Matrix algebra, Metallic matrix composites, Molecules, Silicon alloys, Vapor deposition, Adlayers, Commercial aluminum alloys, First-principle density-functional theories, Localized corrosion of aluminums, Scanning Kelvin probe force microscopy, Volta-potential difference, Aluminum alloys
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-33762 (URN)10.1007/s11244-018-0939-9 (DOI)2-s2.0-85045260197 (Scopus ID)
Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2019-06-17Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3029-6493

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