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Örnek, Cem
Publications (10 of 15) Show all publications
Långberg, M., Örnek, C., Zhang, F., Cheng, J., Liu, M., Granaes, E., . . . Pan, J. (2019). Characterization of Native Oxide and Passive Film on Austenite/Ferrite Phases of Duplex Stainless Steel Using Synchrotron HAXPEEM. Journal of the Electrochemical Society, 166(11), C3336-C3340
Open this publication in new window or tab >>Characterization of Native Oxide and Passive Film on Austenite/Ferrite Phases of Duplex Stainless Steel Using Synchrotron HAXPEEM
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2019 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 166, no 11, p. C3336-C3340Article in journal (Refereed) Published
Abstract [en]

A new measurement protocol was used for microscopic chemical analysis of surface oxide films with lateral resolution of 1 mu m. The native air-formed oxide and an anodic passive film on austenite and ferrite phases of a 25Cr-7Ni super duplex stainless steel were investigated using synchrotron hard X-ray photoemission electron microscopy (HAXPEEM). Pre-deposited Pt-markers, in combination with electron backscattering diffraction mapping (EBSD), allowed analysis of the native oxide on individual grains of the two phases and the passive film formed on the same area after electrochemical polarization of the sample. The results showed a certain difference in the composition of the surface films between the two phases. For the grains with (001) crystallographic face // sample surface, the native oxide film on the ferrite contained more Cr oxide than the austenite. Anodic polarization up to 1000 mV/(Ag/AgCl) in 1M NaCl solution at room temperature resulted in a growth of the Cr- and Fe-oxides, diminish of Cr-hydroxide, and an increased proportion of Fe3+ species. by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited.

Place, publisher, year, edition, pages
Electrochemical Society, 2019
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-254081 (URN)10.1149/2.0421911jes (DOI)000470207900001 ()
Note

QC 20190625

Available from: 2019-06-25 Created: 2019-06-25 Last updated: 2019-07-09Bibliographically approved
Kharitonov, D. S., Sommertune, J., Örnek, C., Ryl, J., Kurilo, I. 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, 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.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Aluminium, Alloy, Raman spectroscopy, SEM, XPS, Vanadate inhibitor
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-244484 (URN)10.1016/j.corsci.2018.12.011 (DOI)000457950400023 ()2-s2.0-85059158841 (Scopus ID)
Note

QC 20190321

Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2019-04-04Bibliographically approved
Anantha, K. H., Örnek, C., Ejnermark, S., Thuvander, A., Medvedeva, A., Sjostrom, J. & Pan, J. (2019). Experimental and modelling study of the effect of tempering on the susceptibility to environment-assisted cracking of AISI 420 martensitic stainless steel. Corrosion Science, 148, 83-93
Open this publication in new window or tab >>Experimental and modelling study of the effect of tempering on the susceptibility to environment-assisted cracking of AISI 420 martensitic stainless steel
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2019 (English)In: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 148, p. 83-93Article in journal (Refereed) Published
Abstract [en]

The resistance to environment-assisted cracking (EAC) of AISI 420 martensitic stainless steel (MSS) was investigated in 0.3 M NaCl solution (room temperature) at constant loads for 30 days. The steel tempered at 250 degrees C was superior to the 500 degrees C-temper, which showed corrosion pits favouring cracking. The fracture surface showed faceted grains, cleavage, striations, and inter- and transgranular cracks, suggesting a mixed stress corrosion cracking (SCC) and hydrogen embrittlement (HE) mechanism as the cause for EAC. Finite element modelling (FEM) indicated strain/stress localization at the mouth of deep pits and at the wall of shallow pits, displaying the favoured locations for pit-to-crack transition.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Martensitic stainless steel, Residual stress, Tempering, Environment-assisted cracking, Pit-to-crack transition
National Category
Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-244485 (URN)10.1016/j.corsci.2018.12.010 (DOI)000457950400009 ()2-s2.0-85058373436 (Scopus ID)
Note

QC 20190321

Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2019-04-04Bibliographically approved
Örnek, C., Långberg, M., Evertsson, J., Harlow, G., Linpe, W., Rullik, L., . . . Pan, J. (2019). Influence of Surface Strain on Passive Film Formation of Duplex Stainless Steel and Its Degradation in Corrosive Environment. Journal of the Electrochemical Society, 166(11), C3071-C3080
Open this publication in new window or tab >>Influence of Surface Strain on Passive Film Formation of Duplex Stainless Steel and Its Degradation in Corrosive Environment
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2019 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 166, no 11, p. C3071-C3080Article in journal (Refereed) Published
Abstract [en]

The effect of surface strain on the passive film evolution of SAF 2507 super duplex stainless steel exposed to ambient air and 0.1 M NaCl solution with varying anodic polarization at room temperature has been investigated using in-situ grazing incidence X-ray diffraction (GIXRD) in combination with electrochemical measurements. Surface strain affected the crystallinity of the passive film as such that the surface oxides/hydroxides were predominantly amorphous, with some minor crystalline CrOOH and FeOOH present in the film. Crystalline CrOOH was seen to diminish in volume upon immersion in the NaCl solution, well-possibly becoming amorphous during anodic polarization, whereas crystalline FeOOH was seen to increase in volume during polarization to the passive potential regime. Strain relaxation, associated with metal dissolution, occurred in both austenitic and ferritic grains during immersion in the electrolyte. Anodic polarization to the transpassive regime led to maximum strain relaxation, occurring more on the austenite than the ferrite. The selective transpassive dissolution nature of the ferrite was significantly reduced due to large strains in the austenite. Passive film breakdown was reflected by enhanced dissolution of Fe, Cr, Mo and Ni occurring simultaneously around 1300 mV vs. Ag/AgCl. 

Place, publisher, year, edition, pages
ELECTROCHEMICAL SOC INC, 2019
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-249787 (URN)10.1149/2.0101911jes (DOI)000463697200001 ()
Note

QC 20190424

Available from: 2019-04-24 Created: 2019-04-24 Last updated: 2019-06-11Bibliographically approved
Örnek, C., Leygraf, C. & Pan, J. (2019). On the Volta potential measured by SKPFM - fundamental and practical pects with relevance to corrosion science. Corrosion Engineering, Science and Technology, 54(3), 185-198
Open this publication in new window or tab >>On the Volta potential measured by SKPFM - fundamental and practical pects with relevance to corrosion science
2019 (English)In: Corrosion Engineering, Science and Technology, ISSN 1478-422X, E-ISSN 1743-2782, Vol. 54, no 3, p. 185-198Article, review/survey (Refereed) Published
Abstract [en]

The Volta potential is an electron-sensitive parameter and describes the ermodynamic propensity of a metal to take part in electrochemical actions. It has found widespread acceptance among corrosion searchers due to its connection to the corrosion potential and its sy measurability in local scale, being often used to study localised rrosion phenomena and micro-galvanic activities. The principle object this paper is to provide a comprehensive, fundamental insight into e meaning of the Volta potential and to define a polarity convention measured potentials by the scanning Kelvin probe force microscopy KPFM) in order to assess local nobilities in microstructures. nditions to relate the Volta potential with the mixed-potential theory e discussed and a possible connection to corrosion phenomena plained. The limitations of the Volta potential as well as the SKPFM chnique are also aimed to be explained, with some practical formation to maximise the output of high quality data.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
Volta potential, scanning Kelvin probe force microscopy, Surface potential, Work function, nobility, corrosion
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-248314 (URN)10.1080/1478422X.2019.1583436 (DOI)000461631700001 ()2-s2.0-85063102596 (Scopus ID)
Note

QC 20190405

Available from: 2019-04-05 Created: 2019-04-05 Last updated: 2019-04-05Bibliographically approved
Örnek, C., Leygraf, C. & Pan, J. (2019). Passive film characterisation of duplex stainless steel using scanning Kelvin probe force microscopy in combination with electrochemical measurements. npJ Materials Degradation, 3(1), 1-8
Open this publication in new window or tab >>Passive film characterisation of duplex stainless steel using scanning Kelvin probe force microscopy in combination with electrochemical measurements
2019 (English)In: npJ Materials Degradation, ISSN 2397-2106, Vol. 3, no 1, p. 1-8Article in journal (Refereed) Published
Abstract [en]

The characterisation of passive oxide films on heterogeneous microstructures is needed to assess local degradation (corrosion, cracking) in aggressive environments. The Volta potential is a surface-sensitive parameter which can be used to assess the surface nobility and hence passive films. In this work, it is shown that the Volta potential, measured on super duplex stainless steel by scanning Kelvin probe force microscopy, correlates with the electrochemical properties of the passive film, measured by electrochemical impedance spectroscopy and potentiodynamic polarisation. Natural oxidation by ageing in ambient air as well as artificial oxidation by immersion in concentrated nitric acid improved the nobility, both reflected by increased Volta potentials and electrochemical parameters. Passivation was associated with vanishing of the inherent Volta potential difference between the ferrite and austenite, thereby reducing the galvanic coupling and hence improving the corrosion resistance of the material. Hydrogen-passive film interactions, triggered by cathodic polarisation, however, largely increased the Volta potential difference between the phases, resulting in loss of electrochemical nobility, with the ferrite being more affected than the austenite. A correlative approach of using the Volta potential in conjunction with electrochemical data has been introduced to characterise the nobility of passive films in global and local scale.

Keywords
Scanning Kelvin probe force microscopy; SKPFM; Volta potential; Duplex Stainless Steel; Corrosion; Electrochemical Nobility; Electrochemical Measurements; Polarization; Electrochemical Impedance Spectroscopy
National Category
Metallurgy and Metallic Materials Materials Engineering Corrosion Engineering Condensed Matter Physics
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-248530 (URN)10.1038/s41529-019-0071-8 (DOI)
Note

QC 20190507

Available from: 2019-04-09 Created: 2019-04-09 Last updated: 2019-05-07Bibliographically approved
Örnek, C. (2019). Stress Corrosion Cracking and Hydrogen Embrittlement of Type 316L Austenitic Stainless Steel Beneath MgCl2 and MgCl2: FeCl3 Droplets. Corrosion, 75(6), 657-667
Open this publication in new window or tab >>Stress Corrosion Cracking and Hydrogen Embrittlement of Type 316L Austenitic Stainless Steel Beneath MgCl2 and MgCl2: FeCl3 Droplets
2019 (English)In: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 75, no 6, p. 657-667Article in journal (Refereed) Published
Abstract [en]

The atmospheric corrosion, as well as environmentally assisted cracking behavior of 316L austenitic stainless steel (UNS S31603) beneath MgCl2 and MgCl2: FeCl3 droplets under elastic and elastic-plastic strain exposed for 6 months at 50 degrees C and 30% relative humidity were investigated. Shallow and deep corrosion sites with filiform corrosion along with stress corrosion cracking (SCC) were formed beneath the salt-laden droplets, and the potential role of hydrogen embrittlement (HE) and crevice corrosion in damage evolution elucidated. Elastic strain (0.1%) was sufficient to cause SCC cracking as well as HE under droplets with 145 mu g/cmth> of chloride, with the severity of cracking increasing with increasing chloride deposition density (CDD). Elastic-plastic strain (0.2%) increased the propensity to both corrosion and SCC/HE, with cracks seen under droplets having CDD as low as 14.5 mu g/cm(2). Elastic-plastic strain was further seen to facilitate and accelerate pitting corrosion, leading to pits with more penetration depth. The extent of corrosion and cracking increases with increasing chloride deposition density, with ferric ions having more severe effect, in particular promoting localized corrosion with multiple nucleation sites. The work reported here was brought into a larger context of stainless steel corrosion and discussed in light of better understanding atmospheric corrosion of structural components such as nuclear waste storage containers.

Place, publisher, year, edition, pages
NATL ASSOC CORROSION ENG, 2019
Keywords
atmospheric corrosion, austenitic stainless steel, crevice corrosion, hydrogen-assisted cracking, pitting corrosion, strain, stress corrosion cracking
National Category
Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-254008 (URN)10.5006/3090 (DOI)000469356600009 ()2-s2.0-85069692291 (Scopus ID)
Note

QC 20190814

Available from: 2019-08-14 Created: 2019-08-14 Last updated: 2019-08-14Bibliographically approved
Örnek, C. & Engelberg, D. L. (2019). Toward Understanding the Effects of Strain and Chloride Deposition Density on Atmospheric Chloride-Induced Stress Corrosion Cracking of Type 304 Austenitic Stainless Steel Under MgCl2 and FeCl3:MgCl2 Droplets. Corrosion, 75(2), 167-182
Open this publication in new window or tab >>Toward Understanding the Effects of Strain and Chloride Deposition Density on Atmospheric Chloride-Induced Stress Corrosion Cracking of Type 304 Austenitic Stainless Steel Under MgCl2 and FeCl3:MgCl2 Droplets
2019 (English)In: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 75, no 2, p. 167-182Article in journal (Refereed) Published
Abstract [en]

Type 304 (UNS S30400) austenitic stainless steel was exposed for 6 months under elastic (0.1%) and elastic/plastic (0.2%) strain to MgCl2 and mixed MgCl2:FeCl3 droplets with varying chloride deposition densities (1.5 mu g/cm(2)-1,500 mu g/cm(2)) at 30% relative humidity (RH) and 50 degrees C. The occurrence of pitting corrosion, crevice corrosion, atmospheric chloride-induced stress corrosion cracking (AISCC), and hydrogen embrittlement (HE) was observed, and the average crack growth rates estimated. Exposure to elastic/plastic strain resulted in longer and more severe cracks. AISCC was found at chloride deposition densities down to 14.5 mu g/cm(2), whereas no cracks were seen at lower deposition densities, with cracks developing at pit or crevice corrosion sites. More severe cracks were seen under MgCl2 droplets as contrasted to mixed MgCl2:FeCl3 salt droplets, which were seen to promote more localized corrosion sites with deeper penetration and in conjunction with shorter crack lengths. Differences in AISCC propagation rates and associated crack morphologies are discussed in relation to understanding long-term atmospheric corrosion exposures.

Place, publisher, year, edition, pages
NATL ASSOC CORROSION ENG, 2019
Keywords
atmospheric-induced stress corrosion cracking, austenitic stainless steel, ferric chloride (FeCl3), hydrogen embrittlement, magnesium chloride (MgCl2), nuclear waste storage
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-244105 (URN)10.5006/3026 (DOI)000456870100009 ()
Funder
Swedish Research Council, 2015-04490
Note

QC 20190219

Available from: 2019-02-19 Created: 2019-02-19 Last updated: 2019-02-19Bibliographically approved
Örnek, C. (2018). Additive manufacturing–a general corrosion perspective. Corrosion Engineering, Science and Technology, 53(7), 531-535
Open this publication in new window or tab >>Additive manufacturing–a general corrosion perspective
2018 (English)In: Corrosion Engineering, Science and Technology, ISSN 1478-422X, E-ISSN 1743-2782, Vol. 53, no 7, p. 531-535Article in journal (Refereed) Published
Abstract [en]

Metallic additive manufacturing will replace some materials produced by conventional fabrication methods in the nearest future. However, corrosion will remain an important aspect needed to be prevented. The corrosion behaviour of additively manufactured alloys has been sparsely studied and very little work has been published so far. In this article, a general discussion about materials produced by additive manufacturing will be provided. 

Place, publisher, year, edition, pages
Taylor and Francis Ltd., 2018
Keywords
3D printing, additive manufacturing, Corrosion, microstructure, Corrosion prevention, Corrosive effects, 3-D printing, Corrosion behaviour, Fabrication method, General corrosion, 3D printers
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-236640 (URN)10.1080/1478422X.2018.1511327 (DOI)000443862200012 ()2-s2.0-85052307586 (Scopus ID)
Funder
Swedish Research Council, 2015-04490
Note

Export Date: 22 October 2018; Article; Correspondence Address: Örnek, C.; Division of Surface and Corrosion Science, Department of Chemical Science and Engineering, KTH Royal Institute of Technology, Drottning Kristinas Väg 51, Sweden; email: ornek@kth.se. QC 20181113

Available from: 2018-11-13 Created: 2018-11-13 Last updated: 2018-11-13Bibliographically 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, 165(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. 165, 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 FeAl3 intermetallic 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.

Place, publisher, year, edition, pages
Electrochemical Society Inc, 2018
National Category
Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-230561 (URN)10.1149/2.0341803jes (DOI)000431790700049 ()2-s2.0-85044021625 (Scopus ID)
Note

QC 20180724

Available from: 2018-07-24 Created: 2018-07-24 Last updated: 2018-07-24Bibliographically approved
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