| 1. |
- Liew, YanHam, et al.
(författare)
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In-situ time-lapse SKPFM investigation of sensitized AA5083 aluminum alloy to understand localized corrosion
- 2020
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Ingår i: Journal of the Electrochemical Society. - : IOP Publishing Ltd. - 0013-4651 .- 1945-7111. ; 167:14
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Tidskriftsartikel (refereegranskat)abstract
- Sensitized AA5083-H2 aluminum alloy was exposed to chloride-laden thin-film electrolyte at ambient temperature (20%–85% relative humidity) and the local Volta potential measured, in-situ and in real-time, using the Scanning Kelvin Probe Force Microscopy, with the intention to elucidate the earliest stage of localized corrosion. Positive Volta potentials vs alloy matrix were measured for magnesium silicides in ambient air, which, however, underwent a severe nobility loss during corrosion, causing their nobility to invert to active potentials (negative) relative to the alloy matrix. The reason for the nobility inversion was explained by the preferential dissolution of Mg2+, which resulted in an electropositive surface. Aluminides, both with and without silicon, were seen to form the main cathodes at all exposure conditions. The local alloy matrix next to closely-separated aluminides were seen to adopt the Volta potential of the neighbor aluminides, which, hence, resulted in local corrosion protection. The phenomenon of nobility adoption introduced in this work raises questions regarding the anode-to-cathode ratio, which was observed to change during corrosion, and the resulting impact to localized micro-galvanic corrosion. This work further demonstrates that it is necessary to measure the Volta potential during corrosion to reflect the true relationship between the Volta potential and corrosion potential or breakdown potential. © 2020 The Author(s).
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| 2. |
- Zhang, Fan, et al.
(författare)
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Anodisation of aluminium alloy AA7075 – Influence of intermetallic particles on anodic oxide growth
- 2020
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Ingår i: Corrosion Science. - : Elsevier Ltd. - 0010-938X .- 1879-0496. ; 164
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure and Volta-potential analyses were conducted to characterise intermetallic-particles (IMPs) in AA7075-T5. EIS and AFM were applied under operando-conditions to investigate anodisation processes. IMPs have pronounced influence on the growth of anodic aluminium oxide (AAO) films resulting in low charge-transfer resistance. Cu-bearing constituents show cathodic-character, whereas Mg2Si and MgZn2 particles show anodic-character. During anodisation, Al7Cu2Fe remain stable with peripheral-dissolution around boundary. De-alloying of S-phase particles leads to the detachment. Mg2Si undergoes de-alloying at low potential, and re-passivation at high potential. MgZn2 dissolves entirely upon anodization. Localised-dissolution in large-IMPs boundaries or nanometre-sized IMPs facilitates bubble evolution, confirming local breakdown of barrier-layer.
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| 3. |
- Örnek, Cem, et al.
(författare)
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Metastable precursor structures in hydrogen-infused super duplex stainless steel microstructure – An operando diffraction experiment
- 2020
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Ingår i: Corrosion Science. - : Elsevier Ltd. - 0010-938X .- 1879-0496. ; 176
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Tidskriftsartikel (refereegranskat)abstract
- We report the evolution of metastable precursor structures during hydrogen infusion in the near-surface region of a super duplex stainless steel. Grazing-incidence x-ray diffraction was employed to monitor, operando, the lattice degradation of the austenite and ferrite phases. Electrochemical hydrogen charging resulted in the splitting of the diffraction peaks of the austenite phase, suggesting the evolution of a metastable precursor structure. This may be explained by the formation of quasi-hydrides, which convert back into the austenite parent structure during hydrogen effusion. The ferrite showed less lattice deformation than the austenite and no phase transformation.
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| 4. |
- 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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| 5. |
- Örnek, Cem, et al.
(författare)
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Real-Time Corrosion Monitoring of Aluminum Alloy Using Scanning Kelvin Probe Force Microscopy
- 2020
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 167:8
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of the Volta potential of grade AA6063-T5 aluminum alloy microstructure with various intermetallic phases (IMP) during corrosion exposure to chloride-laden thin-film electrolytes at ambient temperature has been investigated, in situ and in real-time, using scanning Kelvin probe force microscopy (SKPFM), to gain insight into local corrosion processes. Trenching around micrometer-sized IMPs, de-alloying, oxidation, and the deposition of corrosion products were observed, which led to an inversion of the electrochemical nobility of the IMPs relative to the alloy matrix. Most of the IMPs showed cathodic Volta potentials (high nobility) relative to the matrix at 40%-80% relative humidity (RH), which became anodic (low nobility) when the surface was moistened with aqueous sodium chloride at elevated moisture (76%-87% RH) producing concentrations up to 5-6 M of chloride. The change of the Volta potential correlated with the onset and progress of corrosion and a nobility inversion of IMPs relative to the alloy matrix was observed. The corrosion behavior and the reasons for galvanic activities among microstructural constituents were elucidated and brought into a broader context to understanding localized corrosion.
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| 6. |
- Örnek, Cem, et al.
(författare)
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Time-resolved grazing-incidence X-ray diffraction measurement to understand the effect of hydrogen on surface strain development in super duplex stainless steel
- 2020
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 187, s. 63-67
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Tidskriftsartikel (refereegranskat)abstract
- Grazing-incidence x-ray diffraction was employed to measure, operando, during electrochemical hydrogen charging, the lattice strain development of the near-surface in super duplex stainless steel under applied tensile load. Hydrogen absorption led to the formation of tensile strains in both the austenite (gamma) and ferrite (delta) phases perpendicular to the loading axis, whereas compressive strains were formed in the ferrite phase parallel to the loading direction, despite the acting tensile load. The earliest stages of degradation are discussed in light of understanding hydrogen embrittlement.
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