Corrosion Potential Fluctuation Research Articles

Advanced indentation technique for strength evaluation of hard thin films

A new hybrid technique for studying the fracture mechanism and strength of hard thin film is developed. The technique utilizes acoustic emission (AE) data, corrosion potential fluctuation (CPF) data and finite element method (FEM) for Vickers indentation test. This method was applied to TiN film deposited by PVD method on four metallic substrates of austenitic stainless steel, carbon steel, forging steel and pure iron.We detected both the AE and CPF from equidistant ripple cracks or step-wise terraces produced outside of the indentation during loading in a buffer solution (H3PO4, pH 6.86). Characteristic potential fluctuations, termed as a RD-type CPF (rapid drop to active potential and gradual recovery) and strong AEs were simultaneously produced by Mode-I ripple cracks of the film. They were produced by film bending during the penetration of the pyramidal indenter. The number of ripple cracks observed during indentation agreed well with that of RD-type CPF. Detailed analysis indicated the generation of ripple cracks at a constant distance Lc. The value of Lc can be predicted by the RD-type CPF timing and the penetration rate of the indenter. Bending strength of the film was estimated by FEM using the Lc value. Intrinsic strength of the TiN film, determined by subtraction of residual stress, was measured as 0.9–1.4 GPa. These values are almost constant independent of the substrate material and consistent with the reported strength of 1.2 GPa.

酸化物を生成する塩化物ＳＣＣにおけるＡＥと電位振動

Both the acoustic emission (AE) and corrosion potential fluctuation were monitored for chloride SCC of sensitized Type-304 steel plate under bi-axial stress state. Branched SCCs were produced from rectangular-shaped corrosion pits initiated by falling-off of surface grains and filled with chromium oxide in 30mass% MgCl2 solution (363K). Both the AE and potential fluctuation were simultaneously detected at corrosion pit formation and SCC propagation. Two types of AE (Type-I and Type-II) were monitored. Type-I AEs with higher frequency components were detected during the pit growth and supposed to be produced by falling-off of surface grains due to intergranular attack, while a number of Type-II AEs (about 12,500 counts) with low frequency components were detected at SCC progression and supposed to be produced by cracking of the oxides. Though the AEs detected during SCC test are not the primarily signals from the SCC itself, secondary AE can be usefully utilized to monitor the SCC initiation and propagation as well as the corrosion potential fluctuation.

P61 アコースティック・エミッションと腐食電位揺動法による応力腐食割れの感受性評価(OS13)

P61 アコースティック・エミッションと腐食電位揺動法による応力腐食割れの感受性評価(OS13)

2823 AEと腐食電位揺動を用いた二相ステンレス鋼の環境助長割れのメカニズム(S37-1 非破壊評価とモニタリング(1),S37 非破壊評価とモニタリング)

2823 AEと腐食電位揺動を用いた二相ステンレス鋼の環境助長割れのメカニズム(S37-1 非破壊評価とモニタリング(1),S37 非破壊評価とモニタリング)

541 硬質表面膜の破壊機構研究のためのAEと腐食電位振動解析(OS 非破壊評価とモニタリング(3))

541 硬質表面膜の破壊機構研究のためのAEと腐食電位振動解析(OS 非破壊評価とモニタリング(3))

Corrosion Process Monitoring Using Wavelet Analysis

The objective of this paper is to explore the use of wavelet transform methods in the characterization and identification of intensity and type of localized corrosion using electrochemical noise (in this case, fluctuations in potential). A series of experiments were conducted using two identical stainless steel electrodes inserted into known corrosive media. The fluctuations in corrosion potential (electrochemical noise) generated from these electrodes were monitored periodically (about every hour) over a few days. These fluctuations were stored in blocks of 1024 data points (collected at 1 Hz). They were analyzed by using conventional signal processing techniques in the time and frequency domains as well as by using wavelet techniques in the time-frequency phase plane. The results were compared with microscopic visual examination of the corroded surface to correlate the electrochemical noise signal with the type and extent of corrosion. The results show that wavelet transforms hold promise in decoding this noise pattern. A method to compute the corrosion intensity from the phase plane data is proposed and is in qualitative agreement with the experimental results.

腐食電位振動の逆設定による局部アノード電流の推定

腐食電位振動の逆設定による局部アノード電流の推定

３５ｍａｓｓ％ＭｇＣｌ２水溶液を用いたＳＵＳ３０４ステンレス鋼の応力腐食割れ試験のき裂進展期において観測される台形状電位振動

In the previous paper, the trapezoidal potential fluctuation was observed during the propagation stage of stress corrosion cracking (SCC). However, it had not been examined whether this potential fluctuation had a direct relation to SCC phenomenon. In this paper, the source of the trapezoidal potential fluctuation was investigated. A 35 mass% MgCl2 (353K) solution was employed similarly to the previously reported experiment. Potential fluctuation was measured against an Ag/AgCl reference electrode with a digital voltmeter at a sample frequency of 2.56Hz. The correlation between the elongation rate of the specimen and the potential fluctuation was examined. If the trapezoidal potential fluctuation had a direct relation to the SCC phenomenon, the elongation rate and the potential fluctuation should have a negative correlation. However, these two values correlated positively. The potential fluctuation change by unloading during the experiment was measured. Even after unloading, the trapezoidal potential fluctuation generated continuously. The effect of solution stirring on the corrosion potential fluctuation was also examined. The trapezoidal potential fluctuation disappeared when the solution was stirred. It was estimated that the trapezoidal potential fluctuation was caused by a perturbation of the concentration of dissolved oxygen in the proximity of sample surface. Therefore, it was judged that the fluctuation was not directly related to the SCC phenomenon.

３５ｍａｓｓ％ＭｇＣｌ２水溶液を用いたＳＵＳ３０４ステンレス鋼の応力腐食割れ試験において観測される腐食電位振動

Corrosion potential fluctuation of SUS304 stainless steel during stress corrosion cracking (SCC) was observed in a 35 mass% MgCl2 (353K) solution. The potential fluctuation was measured against an Ag/AgCl reference electrode with a digital voltmeter at a sample frequency of 2.56Hz. During the propagation stage of SCC, a trapezoidal potential fluctuation was observed, whose amplitude and frequency were about 1mV and one or a few times each 3.6ks, respectively. When the experiment was carried out without loading, the trapezoidal potential fluctuation was not detected. The effect of solution temperature on the corrosion potential fluctuation was also examined. An amplitude and an occurrence frequency of the trapezoidal potential fluctuation decreased with a decrease in temperature. The critical temperature for the SCC in the chloride solution environment had been reported to be 323K. The trapezoidal potential fluctuation disappeared at the temperature lower than 333K. Therefore, it was estimated that the trapezoidal potential fluctuation was only generated during the propagation stage of SCC.

腐食防食小特集 応力腐食割れ試験における腐食電位振動の新しい解析方法

Corrosion potential fluctuation was analyzed to investigate the stress corrosion cracking of SUS304 stainless steel immersed in 42 mass% MgCl2 solution. A potential difference between the specimen and the Ag/AgCl reference electrode was measured with a precise digital voltmeter at a sampling frequency of 2.56Hz. Elongation of the specimen was measured with a differential transformer at 10s interval, for the computation of elongation rate.From an electrochemical point of view, the measured corrosion potential was divided into a component of the signal shifted to a more noble potential (Signal of Repassivation) and the one shifted to a less noble potential (Signal of Film Breakdown). These two types of signals were extracted from the sampling data by use of the differential coefficient at each data point. To avoid an errorr in the FFT calculation, the extracted signal was extended symmetrically. Then, a power spectra density (PSD) was calculated by FFT algorithm for each type of signal.The difference in PSD level between two types of signal showed a good correlation with the elongation rate of the specimen. During the time when the elongation rate increased, the value of PSD for the signal of film breakdown became bigger than that of repassivation in the frequency range 10-100 mHz. Conversely, the PSD level for signal of repassivation exceeded that of film breakdown, when the elongation rate decreased or kept a constant value, in the same frequency range.

腐食電位ゆらぎのFFT解析によるSUS 304鋼の熱鋭敏化度の評価

腐食電位ゆらぎのFFT解析によるSUS 304鋼の熱鋭敏化度の評価

Evaluation of Corrosion Inhibitors by Electrochemical Noise Analysis

The corrosion potential fluctuations of aluminum alloy AA 6351 electrodes in 0.5M chloride solutions were recorded both in the absence and in the presence of the following inhibitors: 2‐mercaptopyrimidine, sodium molybdate, and sodium nitrate. The corresponding spectral density plots, calculated over a wide frequency range, are discussed in order to evaluate the possibility of finding the mechanism of action of the additives, by analyzing the electrochemical noise. As a reference, the polarization curves of the alloy in the various solutions are reported.

Analysis of corrosion potential fluctuation for stress corrosion cracking

Corrosion potential fluctuations were analyzed for the understanding of stress corrosion cracking of Type 304 stainless steel immersed in 35 and 42mass% MgCl 2 solutions. They were measured directly from a potential difference between the specimen and the Ag/AgCl reference electrode with a precise digital voltmeter. In 35mass% MgCl 2 solution at 353K, a characteristic potential fluctuation pattern was observed; it dropped to the less noble potential in an early stage and then recovered slowly. In 42mass% MgCl 2 solution at 393K, however, only random potential fluctuations were observed; thus we tried a spectral analysis to get those fluctuations on the frequency domain. Prior to the spectral analysis, we divided the corrosion potential signal into the two components from an electrochemical point of view: the component of the signal which shifts to the more noble potential (Signal of Repassivation) and the one to the less noble potential (Signal of Film Breakdown). The power spectrum density (PSD) for each type of signal was calculated using the fast Fourier transform (FFT) algorithm.

Variation of corrosion potential fluctuations of 18-8 stainless steel with sulfur content

The spectrum analysis of corrosion potential fluctuations is a useful technique to follow the process of localized corrosion of stainless steels [l-3]. A very slight change in the surface state of a specimen, for example micro pit formation, can be detected by the analysis of corrosion potential fluctuations [3]. In this note, we attempt to apply the spectrum analysis of corrosion potential fluctuations to the evaluation of the influence of sulfide inclusions on corrosion resistance of 18-8 stainless steels. The variation of the psd (power spectral density) of the corrosion potential fluctuations with the sulfur content is investigated for the specimens immersed in a sodium chloride solution. Then, the relationships between the sulfur content and psd are compared with those between the sulfur content and the weight loss of a specimen immersed in a ferric chloride solution.

Evaluation of pit volume by measurement of corrosion potential fluctuations for type 304 stainless steel

Examen, a partir des mesures du potentiel de corrosion, des relations existantes entre la periode de propagation de la piqure et son volume dans le cas d'un acier inoxydable type 304 en milieu 4MNaCl-0,1M NaClO

Spectrum Analysis of Corrosion Potential Fluctuations for Localized Corrosion of Type 304 Stainless Steel

Fluctuations of corrosion potential have been analyzed for localized corrosion of Type 304 stainless steel immersed in solutions containing . Potential fluctuations were sampled by a microcomputer, and power spectra were calculated by the fast Fourier transform (FFT). Acoustic emission (AE) was also measured to investigate origins of the potential fluctuations. It was found that formation and repassivation of micropits was confirmed by the potential fluctuations in the form of rapid drop followed by slow rise. When crevice corrosion was proceeding, potential fluctuations in the form of rapid rise followed by slow drop were observed. The absolute values of the slope of power spectral density (psd) for formation and repassivation of micropits were smaller than those for crevice corrosion in the frequency range of 0.01–0.1 Hz.

A new evaluation procedure for detecting the material degradation of a CrMoV turbine rotor steel.

A CrMoV turbine rotor retired after long service operation (22 years at 500°C) was investigated to characterize the material degradation due to temper embrittlement by use of three different kinds of techniques ; the electrochemical polarization curve (EPC) method, the electrochemical noise analysis (ENA) and the small punch (SP) test. Grain boundary embrittlement due to phosphorous segregation can be detected as a change in repassivation behavior in the EPC method ; a significant difference in corrosion potential fluctuation in ENA ; and a shift of SP transition temperature. Diagrams for evaluating the temper embrittlement of a CrMoV turbine rotor were also proposed. Furthermore, a realistic and rational procedure for evaluating material degradation during service operation has been also discussed by combined EPC, ENA and SP methods.

アルミニウム表面上で成長しているピットによる腐食電位変動の変化

アルミニウム表面上で成長しているピットによる腐食電位変動の変化

The Advantages of Galvanostatic Polarization Resistance Measurements

Abstract A routine versatile galvanostatic procedure is described for measuring corrosion rate by polarization resistance. The galvanostatic procedure has been most useful and effective under transient conditons when corrosion rate and corrosion potential are changing with time or when relatively rapid corrosion potential fluctuations are present due to localized corrosion. At each step of the procedure, it is possible to monitor polarization to steady-state, a condition which has been found essential for accurate measurement of polarization resistance, especially at low corrosion rate. Comparisons are made with potentiodynamic scanning methods which have been favored in recent years.