Frequency Analysis of Transients in Electrochemical Noise of Superalloys Waspaloy and Ultimet

Abstract

Nickel or Cobalt-based superalloys represent an important class of engineering materials, finding widespread application in critical components within the gas turbine engines used for jet propulsion and electricity generation. This research aimed at the frequency analysis of transients in electrochemical noise of Waspaloy and Ultimet superalloys, immersed in 3.5 wt.% in H2SO4 and NaCl solutions at two different temperatures, 25 and 60 °C. Localized corrosion behavior of superalloys was assessed using the electrochemical noise technique (EN) according to ASTM-G199 standard. Three different statistical methods filtered the EN signal, and the polynomial method was employed to obtain the noise resistance (Rn), the localization index (LI), skew and kurtosis, and the power spectral density analysis (PSD). Results indicate that the current and potential noise transients have a better behavior with better clarity when a polynomial is used to show a localized corrosion kurtosis for both superalloys.

Electrochemical Noise Measurements on Titanium Regarding Implant Applications

“…Without a background correction, it is not possible to identify and analyze the recorded signals sufficiently. [ 4 ] This is the case because upon immersion of the sample, the open‐circuit potential starts to approach an constant value. This process usually takes up to several hours.…”

“…It was further proposed that the Skewness and Kurtosis values of the time‐domain data can be used to identify the predominant corrosion mechanism. [ 4 ] Skewness and Kurtosis represent the third and fourth statistical moment and are calculated according to Equation () and (), respectively, where x i represents each individual data point of the current or the potential measurements and x ¯ the respective mean value. Further, σ represents the standard deviation of either the current or the potential noise.…”

“…It was proposed that the corrosion mode can be assigned by calculating and comparing the slopes between these points. [ 4 ] It must be noted that this technique is not considered as a reliable method for evaluation. Because of that, it must be seen as an experimental tool and cannot be used for definitive evaluation.…”

“…However, this current or potential can possibly influence the corrosion system and alter the measured parameters. [ 4,5 ] A technique circumventing these problems is the ECN measurement. While it is not a new type of measurement, it is sparsely used in modern corrosion science.…”

Electrochemical corrosion behavior of Ti‐3Mo alloy under different accelerated corrosion tests

“…Titanium (Ti) alloys are widely used in important industrial fields such as oil pipelines, aerospace, automobile manufacturing, marine drilling, and biomedicine due to their high specific strength, [1][2][3][4] low elastic modulus, [5][6][7] good electrical conductivity, [8,9] and fracture toughness, [10,11] as well as excellent corrosion resistance. [12][13][14] As a functional and structural material with excellent overall properties, the composition design, microstructure, mechanical characterization, and corrosion performance of Ti alloys have been extensively studied, [15][16][17][18] and the types of Ti alloys have gradually developed into hightemperature Ti alloys, [19,20] high-strength Ti alloys, [21,22] corrosion-resistant Ti alloys, [23,24] and biomedical Ti alloys, [25,26] which has great actual application value. In view of its excellent corrosion resistance, Ti alloy materials are more and more widely used in coastal atmospheric marine environments and soil corrosion environments.…”