Anna Arutunow, Artur Zieliński and Mateusz T. Tobiszewski
The purpose of this paper is to present the results of an atomic force microscopy (AFM) based approach to local impedance spectroscopy (LIS) measurement performed on AA2024 and…
Abstract
Purpose
The purpose of this paper is to present the results of an atomic force microscopy (AFM) based approach to local impedance spectroscopy (LIS) measurement performed on AA2024 and AA2024‐T3 aluminium alloys.
Design/methodology/approach
AFM‐LIS measurements were performed ex‐situ without the electrolyte environment, so in fact the electrical not electrochemical impedance was obtained.
Findings
Relative local impedance values recorded for AA2024 alloy during the researches carried out were maximally approximately three orders of magnitude higher than the ones obtained for age‐hardened AA2024‐T3 alloy. Moreover, in the case of AA2024‐T3 alloy, a region located in the interior of α crystals exhibited localized impedance one order of magnitude higher than that measured at its grain boundary when affected by intergranular corrosion.
Originality/value
The paper presents differences in localized impedance between grain and grain boundaries activity.
Details
Keywords
The purpose of this paper is to focus on diversification between electrical parameters determined on the basis of instantaneous impedance measurements within the activation and…
Abstract
Purpose
The purpose of this paper is to focus on diversification between electrical parameters determined on the basis of instantaneous impedance measurements within the activation and reactivation scan of dissolution of sensitized AISI 304 stainless steel during a proceeding intergranular corrosion process.
Design/methodology/approach
The investigations were carried out by means of dynamic electrochemical impedance spectroscopy (DEIS). DEIS measurements were conducted “on‐line” while the samples were polarized in agreement with a measurement procedure presented in the ASTM G108‐94 standard, in order to guarantee conditions equivalent with the DL‐EPR tests performed on AISI 304 stainless steel.
Findings
Performed researches revealed the advantages of the DEIS technique over standard double‐loop electrochemical potentiokinetic reactivation (DL‐EPR) tests in the field of intergranular corrosion investigations. Application of the DEIS technique made it possible to trace instantaneous changes in the examined system's impedance versus potential during the intergranular corrosion process. The form of recorded DEIS spectra and obtained distribution of measurement frequencies within the reactivation potential range were equivalent to those obtained for pure iron dissolution in sulfuric acid medium. As a result, instantaneous changes of electrical double layer capacitance and charge transfer resistance as a function of potential have been obtained in the range of activation and reactivation scans.
Originality/value
The paper provides information regarding diversification between the electrical double layer capacitance and the charge transfer resistance determined for sensitized AISI 304 stainless steel with respect to polarization conditions during the standard DL‐EPR test, which were obtained in order to evaluate the susceptibility to intergranular corrosion.
Details
Keywords
Jacek Ryl, Anna Arutunow, Mateusz T. Tobiszewski and Joanna Wysocka
The purpose of this paper is to present a case study of unexpected sensitization to intergranular corrosion of highly resistant AISI 321 steel in petrochemical conditions, where…
Abstract
Purpose
The purpose of this paper is to present a case study of unexpected sensitization to intergranular corrosion of highly resistant AISI 321 steel in petrochemical conditions, where it was subjected to the simultaneous influence of elevated temperature of ∼250°C and vapors from the asphalt production process.
Design/methodology/approach
Corrosion coupons were exposed in an installation carrying asphalt vapors. To identify the susceptibility to intergranular corrosion a standard Strauss test was performed. Scanning electron microscopy (SEM) micrographs show a degree of degradation as a result of local corrosion. Influence of the carburization process occurred during exposure and depletion of chromium in the passive layer and was evaluated using X-ray photoelectron spectroscopy (XPS) and X-ray spectroscopy (EDX) techniques.
Findings
The paper provides information on origin of corrosion of AISI 321 steel in a high-carbon-containing environment. It was found out that long-term exposure can lead to intergranular corrosion in temperatures that are much lower than those that have been considered to be required for sensitization of austenitic steels. The high concentration of carbon introduced during the exposure is stated to be responsible for this effect.
Practical implications
The formation of chromium carbides, leading to intergranular corrosion of the Type 321 stainless steel, is a major concern. The paper reports that in certain petrochemical environments, highly resistant stainless steels, such as AISI 321, can be susceptible to intergranular carbide degradation.
Originality/value
The presence of titanium is not sufficient to increase resistance in multiple environments and sensitization can occur even at relatively low temperatures of ∼250°C.