| 1. |
- Långberg, Marie, et al.
(författare)
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Characterization of Native Oxide and Passive Film on Austenite/Ferrite Phases of Duplex Stainless Steel Using Synchrotron HAXPEEM
- 2019
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Ingår i: Journal of the Electrochemical Society. - : Electrochemical Society. - 0013-4651 .- 1945-7111. ; 166:11, s. C3336-C3340
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Långberg, Marie, 1988-, et al.
(författare)
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Lateral variation of the native passive film on super duplex stainless steel resolved by synchrotron hard X-ray photoelectron emission microscopy
- 2020
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Ingår i: Corrosion Science. - Stockholm, : Elsevier BV. - 0010-938X .- 1879-0496. ; 174
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Tidskriftsartikel (refereegranskat)abstract
- A native passive film on 25Cr-7Ni super duplex stainless steel was analyzed using synchrotron hard X-ray photoemission electron microscopy, focusing on variations between individual grains of ferrite and austenite phases. The film consists of an oxide inner layer and an oxyhydroxide outer layer, in total 2.3 nm thick. The Cr content is higher in the outer than the inner layer, ca. 80 % on average. The Cr content is higher on ferrite than austenite, whereas the thickness is rather uniform. The grain orientation has a small but detectable influence, ferrite (111) grains have a lower Cr content than other ferrite grains.
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| 3. |
- Långberg, Marie
(författare)
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Passivity & Breakdown of Super Duplex Stainless Steel : Studied with Electrochemical & Synchrotron Techniques
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Super duplex stainless steel consists of two phases: austenite and ferrite, and is a highly corrosion resistant material, with a wide range of applications. The corrosion resistance of stainless steels is determined by the performance of a spontaneously formed thin Cr oxide rich film with a thickness of 1-3 nm. This film makes the stainless steel passive towards further oxidation processes, corrosion. The passive film is a dynamic system where degradation and formation reactions occur simultaneously. Super duplex stainless steel is a multi-phase, multielement material which has a high corrosion resistance and the question is whether its microstructure and alloying elements are affecting its passive film properties. This thesis contains two parts: real time synchrotron measurements to study the degradation mechanism during anodic polarization which pushes the material toward oxidation processes; and ex-situ measurements to map the lateral thickness and microscopic elemental distribution in the passive film. The in-situ/operando synchrotron experiments combined several experimental techniques, including X-ray reflectivity (XRR), X-ray diffraction (XRD), X-ray fluorescence (XRF) and electrochemical impedance spectroscopy (EIS), to simultaneously characterize the structure and chemical/electrochemical properties, as well as their changes of the surface region of the samples. It was found that the oxide film became more defective with increasing potential, leading to a decreased density of the passive film. On the other hand, the Ni rich alloy surface layer below the oxide film showed an increasing density, indicating an increased concentration of heavy elements (Mo and Ni). The XRD data showed evidence of nanocrystalline passive film whereas the amorphousness of the passive film increased with increasing potential. The ex-situ investigations employed by hard X-ray photoelectron emission microscopy (HAXPEEM), providing chemical data from individual grains with different crystallographic orientations parallel to the sample plane. The Cr content was higher on the ferrite than the austenite, whereas the thickness was rather uniform. The grain orientation has a small but detectable influence on the thickness and Cr content of the native passive film.
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| 4. |
- Långberg, Marie, 1988-, et al.
(författare)
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Redefining passivity breakdown of super duplex stainless steel by electrochemical operando synchrotron near surface X-ray analyses
- 2019
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Ingår i: npj Materials Degradation. - Stockholm, : Springer Science and Business Media LLC. - 2397-2106. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Passivity determines corrosion resistance and stability of highly-alloyed stainless steels, and passivity breakdown is commonly believed to occur at a fixed potential due to formation and dissolution of Cr(VI) species. In this work, the study of a 25Cr–7Ni super duplex stainless steel in 1 M NaCl solution revealed that the passivity breakdown is a continuous degradation progress of the passive film over a potential range, associated with enhanced Fe dissolution before rapid Cr dissolution and removal of the oxide. The breakdown involves structural and compositional changes of the passive film and the underlying alloy surface layer, as well as selective metal dissolution depending on the anodic potential. The onset of passivity breakdown occurred at 1000 mV/Ag/AgCl, and Fe dissolved more on the ferrite than the austenite phase. With increasing potential, the passive film became thicker but less dense, while the underlying alloy surface layer became denser indicating Ni and Mo enrichment. Rapid Cr dissolution occurred at ≥1300 mV/Ag/AgCl.
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| 5. |
- Ornek, Cem, et al.
(författare)
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Hydrogen-Induced Micro-Strain Evolution in Super Duplex Stainless Steel-Correlative High-Energy X-Ray Diffraction, Electron Backscattered Diffraction, and Digital Image Correlation
- 2022
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Ingår i: FRONTIERS IN MATERIALS. - : Frontiers Media SA. - 2296-8016. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- The local lattice strain evolution during electrochemical hydrogen charging and mechanical loading in 25Cr-7Ni super duplex stainless steel were measured in-situ using synchrotron high-energy x-ray diffraction. Post-mortem electron backscattered diffraction analysis showed that the austenite phase underwent plastic deformation in the near-surface due to hydrogen-enhanced localized plasticity, where the ferrite phase experienced hardening. In bulk regions, the ferrite was the softer phase, and the austenite remained stiff. Digital image correlation of micrographs recorded, in-situ, during mechanical tensile testing revealed intensified plastic strain localization in the austenite phase, which eventually led to crack initiation. The absorption of hydrogen caused strain localization to occur primarily in austenite grains.
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| 6. |
- Zhang, Fan, et al.
(författare)
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Integration of electrochemical and synchrotron-based X-ray techniques for in-situ investigation of aluminum anodization
- 2017
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 241, s. 299-308
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Tidskriftsartikel (refereegranskat)abstract
- Anodization of aluminum alloys AA 6082 and AA 7075 was investigated in-situ with integrated electrochemical and synchrotron-based X-ray reflectivity (XRR) methods providing complementary information about the anodic processes taking place on the alloys. The stepwise potentiostatic polarization measurements reveal dynamic processes of the anodic oxide formation and dissolution, and the following electrochemical impedance spectroscopy measurements detect the break of the native oxide and the growth of typical two-layer anodic oxide film, while the XRR measurements show the growth of entire anodic oxide film whose thickness increases linearly with the increasing applied potential. The results indicate that while a stable anodic oxide can be formed on the both alloys with a similar growth factor, AA 7075 shows a thinner thickness of the barrier layer and a lower resistance of the oxide film. The electrochemical results suggest both localized and uniform anodic dissolution processes, which are more pronounced on AA 7075, demonstrating the effect of alloying elements on the growth of anodic oxides.
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| 7. |
- Örnek, Cem, et al.
(författare)
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In-situ synchrotron GIXRD study of passive film evolution on duplex stainless steel in corrosive environment
- 2018
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Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 141, s. 18-21
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Örnek, Cem, et al.
(författare)
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Influence of Surface Strain on Passive Film Formation of Duplex Stainless Steel and Its Degradation in Corrosive Environment
- 2019
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 166:11, s. 3071-3080
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Örnek, Cem, et al.
(författare)
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Operando time- and space-resolved high-energy X-ray diffraction measurement to understand hydrogen-microstructure interactions in duplex stainless steel
- 2020
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Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 175
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Tidskriftsartikel (refereegranskat)abstract
- Local strain development in the microstructure of a commercial 25Cr-7Ni super duplex stainless steel was mapped using high-energy x-ray diffraction during cathodic hydrogen charging under constant uniaxial load. The infusion of hydrogen resulted in tensile strains in austenite grains, one order of magnitude larger than those in the ferrite. Most strain evolution occurred at the near-surface, with compensating compressive forces developed in underlying regions, with up to two-times more compression occurring in the ferrite than the austenite. The strains along the loading axis were more pronounced than in the transverse direction, in which mostly compressive strains developed in the ferrite.
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