Artur Zieliński

Effect of microstructure on stress corrosion cracking of an Al-Zn-Mg-Cu alloy

The susceptibility to stress corrosion cracking (SCC) of the Al-Zn-Mg-Cu French 7010 alloy of different temper has been investigated by Slow Strain Rate Testing. The tests have been carried out at strain rate ranged between 10−5 and 10−7s−1, at corrosion potential and at cathodic polarisation, in NaCl and NaCl + As2O3 solution. The lowest susceptibility to SCC of overaged alloy has been explained by presence of large phase precipitates which increased the alloy resistance to pitting and intergranular corrosion, changed the conditions of crack initiation and trapped the absorbed hydrogen.

Pitting corrosion in steel and electrochemical noise intensity

Electrochemical noise data in the presence of pitting corrosion were analyzed. A correlation between the intensity of the observed noise and mass loss of steel electrodes was recognized. The registered noise was decomposed into a set of band limited components using wavelet transform. It has been observed that the standard deviation of the chosen component was more strictly correlated with mass loss of electrodes than the standard deviation of the other components. The frequency band of the chosen component was adequate to the band where energy of transients, typical for pitting corrosion dominated. The measurement results were obtained only for the limited number of electrodes due to a very long time of noise observation.

Detection of random transients caused by pitting corrosion

The corrosion processes can be estimated by measurements of electrochemical noise. Noise can be observed as current and voltage fluctuations in a three-electrode setup. The presence of pitting corrosion is manifested as transients in current and voltage fluctuations. For an estimation of the pitting corrosion presence in the recorded current fluctuations, the detection of the characteristic transients has been performed. For the determination of transient occurrence, a detection algorithm of the local changes in a spectrogram of the current fluctuations has been used. The spectrogram has been derived using short-time Fourier transform (STFT). The detected transients, characteristic of pitting corrosion, have been filtered. A time-varying filtering has been performed using an iterative algorithm, presented in the paper.

Application of dynamic impedance spectroscopy to atomic force microscopy

Abstract Atomic force microscopy (AFM) is a universal imaging technique, while impedance spectroscopy is a fundamental method of determining the electrical properties of materials. It is useful to combine those techniques to obtain the spatial distribution of an impedance vector. This paper proposes a new combining approach utilizing multifrequency scanning and simultaneous AFM scanning of an investigated surface.

Local impedance imaging of boron-doped polycrystalline diamond thin films

Local impedance imaging (LII) was used to visualise surficial deviations of AC impedances in polycrystalline boron-doped diamond (BDD). The BDD thin film electrodes were deposited onto the highly doped silicon substrates via microwave plasma-enhanced CVD. The studied boron dopant concentrations, controlled by the [B]/[C] ratio in plasma, ranged from 1 × 1016 to 2 × 1021 atoms cm−3. The BDD films displayed microcrystalline structure, while the average size of crystallites decreased from 1 to 0.7 μm with increasing [B]/[C] ratios. The application of LII enabled a direct and high-resolution investigation of local distribution of impedance characteristics within the individual grains of BDD. Such an approach resulted in greater understanding of the microstructural control of properties at the grain level. We propose that the obtained surficial variation of impedance is correlated to the areas of high conductance which have been observed at the grain boundaries by using LII. We also postulate that the origin of high conductivity is due to either preferential boron accumulation, the presence of defects, or sp2 regions in the intragrain regions. The impedance modulus recorded by LII was in full agreement with the bulk impedance measurements. Both variables showed a decreasing trend with increasing [B]/[C] ratios, which is consistent with higher boron incorporation into BDD film.

Continuous‐Frequency Method of Measurement of Electrode Impedance

Abstract A mathematical basis of a new method of measurement of electrode impedance is presented. The method uses a non‐stationary perturbation signal whose frequency varies linearly with time. The amplitude of a non‐stationary sine perturbation signal is constant. The recording and analysis of both the perturbation and response signals allow the determination of continuous‐frequency impedance spectra. Simultaneous time‐frequency analysis of the voltage perturbation signal and current response signal was performed using the Gabor transformation.

Evaluation of reinforcement corrosion rate in concrete structures by electrochemical noise measurements

Experimental results on the polarization resistance estimation in a three-electrode setup that consists of two carbon steel electrodes and the silver reference electrode are presented. The corrosion rate varies with the conditions changing inside the concrete structure due to its irregular wetting in an aqueous solution of NaCl. The change of polarization resistance of a single steel electrode can be identified by voltage and current electrochemical noise measurements. The observed change does not exceed the factor of a few times of the originally recognized value. The newly proposed method of electrochemical noise analysis for monitoring of swift corrosion rate changes is presented in detail.

The comparative study of different methods of spectral analysis of electrochemical oscillations

Abstract Electrochemical oscillations frequently accompany the electrodissolution of metals. They often exhibit non-stationary character. Accordingly a need for analysis in the joint time–frequency domain appears. Comparison of three new methods: STFT, wavelet transformation and Wigner–Ville distribution is presented in this paper. Advantages of these methods are pointed out and the difference between Fourier and joint time–frequency techniques is explained.

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.

Implementation and Validation of Multisinusoidal, Fast Impedance Measurements in Atomic Force Microscope Contact Mode

This study presents a novel approach to impedance measurements. The methodology discussed is limited to contact in the sample-probe system under ambient conditions without the presence of electrolyte. Comparison with results of direct and alternating current measurements for well-defined metallic surfaces are made. In spite of idealization related to the type of contact examined, the proposed technique provides an improvement of traditional impedance measurement related to sequential changes in system perturbation compared with the sine wave superposition type.