| 1. |
- Helbert, Varvara, et al.
(författare)
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Corrosion behavior of additively manufactured AISI 316L stainless steel under atmospheric conditions
- 2022
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Ingår i: Materials and corrosion - Werkstoffe und Korrosion. - : John Wiley and Sons Inc. - 0947-5117 .- 1521-4176. ; 73:11, s. 1833-
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Tidskriftsartikel (refereegranskat)abstract
- This study investigated the corrosion behavior of AISI 316L produced by direct energy deposition (DED). Microstructural and chemical analysis showed a homogeneous distribution of Si and Si–Mn inclusions of 0.5–1 µm and the Cr and Mo enrichment within interdendritic areas. Scanning Kelvin probe analysis of additively manufactured stainless steel highlighted a regular “striped-like” surface potential feature with a potential gradient of 30 mV for a mean value of 0.320 ± 0.017 V versus standard hydrogen electrode. It can be related to the presence of the residual stress in the oxide film and the complex thermal history due to the fabrication process. A cyclic corrosion test simulating atmospheric conditions revealed the same corrosion properties for stainless steel fabricated by DED compared to cold rolled one. Various surface preparations of 316L were also exposed for corrosion tests. It was found that the “as-received” and “brushed” surfaces exhibited poorer corrosion resistance due to the presence of an as-build defective layer. However, prior passivation of brushed surface, machining, or mechanical grinding down to P1200 improve significantly the corrosion resistance. © 2022 French Corrosion Institute part of RISE Research Institutes of Sweden. Materials and Corrosion published by Wiley-VCH GmbH.
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| 2. |
- Helbert, Varvara, et al.
(författare)
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Effect of cathodic polarisation switch-off on the passivity and stability to crevice corrosion of aisi 304l stainless steel
- 2021
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 14:11
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Tidskriftsartikel (refereegranskat)abstract
- The effects of cathodic polarisation switch-off on the passivation of AISI 304L stainless steel in air and its crevice corrosion susceptibility in 3.5 wt.% NaCl aqueous electrolyte were investigated. Scanning Kelvin probe (SKP) data showed that the oxide film is significantly destabilised and the rate of steel passivation in air is slowed down. Thermal desorption analysis (TDA) highlighted that hydrogen absorption is proportional to the applied cathodic current density. A special crevice corrosion set-up was designed to realise simultaneous reproducible monitoring of potential and galvanic current to study the impact of prior cathodic polarisation on crevice corrosion onset. © 2021 by the authors.
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| 3. |
- Helbert, Varvara, et al.
(författare)
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Hydrogen effect on the passivation and crevice corrosion initiation of AISI 304L using Scanning Kelvin Probe
- 2021
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Ingår i: Corrosion Science. - : Elsevier Ltd. - 0010-938X .- 1879-0496. ; 182
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Tidskriftsartikel (refereegranskat)abstract
- Scanning Kelvin Probe was applied to study passivation of AISI 304L stainless steel after cathodic polarisation. The rate of passivation in air decreased as a function of duration and current density. X-ray Photoelectron Spectroscopy showed enrichment of the surface film by hydroxides of Fe (II) that was the result of hydrogen effusion from the bulk. SKP measured a decreased potential drop in the passive film. Pre-polarisation accelerates the crevice corrosion of steel in presence of chlorides. Using SKP mapping, increased hydrogen sub-surface concentration and lower level of passivity was observed in anodic zones of the crevice.
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| 4. |
- Helbert, Varvara, et al.
(författare)
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Kinetics of corrosion reactions on press hardened steel in atmospheric conditions under thin electrolyte films
- 2023
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Ingår i: Electrochimica Acta. - : Elsevier Ltd. - 0013-4686 .- 1873-3859. ; 458
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Tidskriftsartikel (refereegranskat)abstract
- Steels with high mechanical performance are prone to hydrogen embrittlement and environmental assisted cracking. Under atmospheric corrosion conditions, the source of hydrogen can be the steel corrosion process itself or galvanic coupling with a metallic coating. Electrochemical behaviour of Press Hardened Steel (PHS) under electrolyte films of different thicknesses using local electrochemical techniques was studied on a fundamental level. Scanning Vibrated Electrode Technique (SVET) was applied to study the evolution and localization of the corrosion process during PHS immersion in NaCl electrolyte. Kelvin Probe (KP) was used as a reference electrode to obtain cathodic and anodic polarization curves on PHS surfaces which were covered by thin electrolyte films (60 to 500 µm) of 0.1 M NaOH and 0.6 M NaCl. For both electrolytes, a strong increase in the oxygen reduction rate due to the decreasing of electrolyte thickness has been clearly demonstrated. Data are correlated well with a theoretical plot determined by Nernst-Fick equation. The influence of the rust layers on the kinetics of corrosion reactions under thin electrolyte films was investigated using KP. © 2023
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| 5. |
- Nazarov, Andrei, et al.
(författare)
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Scanning Kelvin Probe for Detection in Steel of Locations Enriched by Hydrogen and Prone to Cracking
- 2023
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Ingår i: Corrosion and Materials Degradation. - : Multidisciplinary Digital Publishing Institute (MDPI). - 2624-5558. ; 4:1, s. 158-173
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen, due to corrosion processes, can degrade high strength steels (HSS) through embrittlement and stress corrosion cracking mechanisms. Scanning Kelvin probe (SKP) mapping of surface potential was applied, to visualize the locations with an increased subsurface concentration of hydrogen in mild steel and martensitic HSS. This work can help to determine the reasons behind hydrogen localization in a steel microstructure, leading to embrittlement and hydrogen-assisted cracking. Cathodic charging was used to insert hydrogen, which decreased the steel potential. Hydrogen effusion in air passivates steel, increasing the potential of HSS and mild steel. The passivation of steels was monitored depending on different conditions of cathodic pre-charging and the amount of absorbed hydrogen. The SKP could determine the area of diffusible hydrogen and the area of cracks. In addition, low potential locations linked to the hydrogen trapped in the deformed HSS microstructure were also determined, which delayed the steel passivation. Mild steel showed a uniform potential distribution related to interstitial hydrogen, without potential extremes attributed to locally accumulated hydrogen. Thus, SKP sensing can detect locations containing increased concentrations of hydrogen and sensitive to steel cracking.
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| 6. |
- Ootsuka, Shinji, et al.
(författare)
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Quantification of subsurface hydrogen in corroding mild steel using Scanning Kelvin Probe calibrated by electrochemical permeation technique
- 2023
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Ingår i: Corrosion Science. - : Elsevier Ltd. - 0010-938X .- 1879-0496. ; 221
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Tidskriftsartikel (refereegranskat)abstract
- Scanning Kelvin probe (SKP) can be applied for mapping of subsurface hydrogen in steels. The good spatial resolution is combined with poor quantification. Controversy, the electrochemical permeation technique (EPT) is extremely sensitive to hydrogen flux but has low spatial resolution. Thus, a local hydrogen quantification method using SKP measurements calibrated by EPT was developed. The fixed amount of hydrogen flux in mild steel membrane was obtained by cathodic polarization and was detected using the two methods. A semi-logarithmic relationship between SKP potential drop and the hydrogen sub-surface concentration underneath of the corroding surface was established. SKP quantification was applied for mapping the subsurface hydrogen in steel corroding under various atmospheric corrosion conditions.
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| 7. |
- Vucko, Flavien, et al.
(författare)
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Quantification of Hydrogen Flux from Atmospheric Corrosion of Steel Using the Scanning Kelvin Probe Technique
- 2023
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Ingår i: Metals. - : MDPI. ; 13:8, s. 1427-1427
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Tidskriftsartikel (refereegranskat)abstract
- The atmospheric corrosion of high-strength steels can lead to hydrogen absorption directly linked to hydrogen embrittlement or delayed fracture phenomena. A scanning Kelvin probe (SKP) and electrochemical permeation technique (EPT) were applied to correlate the potential of an oxidized surface with the flux of hydrogen across a thin steel membrane. The side of the membrane opposite the corroding or electrochemically charged area was analyzed. The potential drop in the oxide was calibrated in terms of surface hydrogen activity, and SKP can be applied in situ for the mapping of hydrogen distribution in the corroding metal. A very low flux of hydrogen can be characterized and quantified by SKP, which is typically observed under atmospheric corrosion conditions. Therefore, hydrogen localization that drives steel durability under atmospheric corrosion conditions can be evaluated.
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