Electrochemical Noise Analysis of the Corrosion of Titanium Alloys in NaCl and H2SO4 Solutions

Abstract

Titanium alloys have been used in aerospace, aeronautic, automotive, biomedical, structural, and other applications because titanium alloys have less density than materials like steel and support higher stress than Al-alloys. However, components made of titanium alloys are exposed to corrosive environments, the most common being industrial and marine atmospheres. This research shows the corrosion behavior of three titanium alloys, specifically Ti-CP2, Ti-6Al-2Sn-4Zr-2Mo, and Ti-6Al-4V with α, near α, and α + β alloys phases. Alloys were exposed in two electrolytes to a 3.5 wt. % H2SO4 and NaCl solution at room temperature, and their electrochemical behavior was studied by electrochemical noise technique (EN) according to ASTM ASTM-G199 standard. EN signal was filtered by three different methods, and the polynomial method was employed to obtain Rn, kurtosis, skew, and the potential spectral density analysis (PSD). The wavelets method was used, from which energy dispersion plots were obtained. The last method was Hilbert–Huang Transform (HHT), where Hilbert Spectra were analyzed. Results indicated that Rn compared with PSD showed that Ti-6Al-2Sn-4Zr-2Mo presented less dissolution in both electrolytes. Statistical methods showed that the passive layer created on Ti alloys’ surfaces is unstable; this condition is notable for Ti-6Al-2Sn-4Zr-2Mo in NaCl solution.

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

“…Localization index (LI) was not considered because Mansfeld and Sun [54] in 1995 concluded that LI can present limitations and should be used with discretion. In 2001, Reid and Eden [55] developed a patent where they identified corrosion type based on statistical moments with skewness and kurtosis (Equations ( 6) and ( 7)), which are the 3rd and 4th statistical moments [54][55][56][57][58][59][60][61]:…”

“…Some research [25][26][27][28][29][30]36,37,[53][54][55][56][57][58] indicates that Several EN procedures correlating time-dependent fluctuation of current and potential during the corrosion process have been used to indicate the type of corrosion occurring. For instance, it is well recognized that the primary source of electrochemical noise is the passive film breakdown process and repassivation process.…”

“…The frequency zero limit (Ψ 0 ) gives material dissolution information because PSD is related to the total energy present in the system [22]. It is essential to clarify that material dissolution is only present in the current PSD [56,57]. The following table was proposed by Mansfeld et al [54] in 1999 to determine the corrosion phenomena occurring on the material surface.…”

“…Z n is calculated by the square root of the PSD division of potential and current [56,64]. The electrochemical noise impedance is related to the corrosion resistance, and the inverse is related to conductance and corrosion rate [65,66].…”

Effect of Cathodic Protection on Reinforced Concrete with Fly Ash Using Electrochemical Noise

“…The Fast Fourier Transform includes power spectral density, noise impedance, etc; and time-frequency domains method; have the analysis Hilbert-Huang transform, Discrete Wavelet transform, Stockwell transform and others) [ 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. LI , skewness, and kurtosis values have been related to different corrosion types and the asymmetry of the distribution of EN data [ 47 , 48 , 49 , 50 , 51 , 52 ].…”