A. Arutunow

Comparative Electrochemical Analysis of the Passive Layer Cracking Process on Aluminum Alloys Performed by Means of DC and AC Techniques

In this paper the passive layer cracking process that occurs under tensile stresses and anodic polarization conditions on AA1050, AA5052, AA5056, and AA7005 aluminum alloys was examined by means of direct current (dc) technique, dynamic electrochemical impedance spectroscopy (DEIS), and acoustic emission (AE). Research revealed the advantage of DEIS and AE methods over the dc one. It was also possible to determine the exact moment of the passive layer cracking on investigated aluminum alloys.

Localized impedance measurements of AA2024 and AA2024‐T3 performed by means of AFM in contact mode

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.

Aspects of intergranular corrosion of AISI 321 stainless steel in high-carbon-containing environments

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 i...

Instantaneous impedance evaluation of dissolution of AISI 304 stainless steel during intergranular corrosion

– 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., – 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., – 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 systems 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., – 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.

Application of Dynamic Impedance Spectroscopy to Scanning Probe Microscopy

Dynamic impedance spectroscopy, designed for measuring nonstationary systems, was used in combination with scanning probe microscopy. Using this approach, impedance mapping could be carried-out simultaneously with topography scanning. Therefore, correlation of electrical properties with particular phases of an examined sample was possible. The sample used in this study was spheroidal graphite cast iron with clearly defined phases having significantly different properties. Additionally, impedance-force curves were made at graphite precipitation and ferrite matrix to illustrate the relation between impedance and the force applied to a probe.