SPECTRAL ANALYSIS IN THE EVALUATION OF THE ELECTROCHEMICAL BEHAVIOR OF HIGH-ENTROPY GdTbDyHoSc AND GdTbDyHoY ALLOYS

The corrosion behavior of disordered systems, such as high-entropy alloys, exhibit a stochastic random process. To accurately predict and analyze the behavior of these systems in service environments, it is necessary to employ new computational and experimental methods alongside classical electrochemical methods. In this study, we highlighted the effectiveness of using fast Fourier transform and wavelet analysis to assess the corrosion behavior of stochastic systems, using the example of equimolar rare-earth alloys GdTbDyHoSc and GdTbDyHoY. To evaluate the corrosion behavior, we measured the time series of potential fluctuations for the studied samples in a 0.01 M NaCl solution over a 12-hour period, at current densities ranging from 0.2 to 0.5 mA/cm². Applying the fast Fourier transform method to analyze the obtained time series, we observed that the angular coefficient of the slope of the logarithm of the power spectral density logarithm to the logarithm of frequency increased with higher current density. Specifically, for the GdTbDyHoSc alloy, the coefficient increased from –1.46 to –1.35, indicating the prevalence of general corrosion dissolution. In contrast, for the GdTbDyHoY alloy, the coefficient increased from –1.93 to –1.77, suggesting the dominance of localized dissolution. Furthermore, we utilized wavelet analysis to process the time series data for both alloys at current densities ranging from 0.2 to 0.5 mA/cm². This analysis allowed us to plot time series scalograms, which visually illustrated the intensity of the corrosion process on the surface of the investigated alloys. From the scalograms, we calculated the values of the global energy spectra distributed over frequency ranges, as well as the values of the total energy of the investigated systems. Interestingly, the GdTbDyHoY alloy exhibited higher total energy values compared to the GdTbDyHoSc alloy. Specifically, the total energy for the GdTbDyHoY alloy increased from 0.97 to 2.03 kV² as the current density increased from 0.2 to 0.5 mA/cm², respectively. For the GdTbDyHoSc alloy, the total energy increased from 0.50 to 0.84 kV². In conclusion, the application of fast Fourier transform and wavelet analysis methods proved to be effective tools for gaining a deep understanding of the corrosion behavior of locally disordered chemical systems, such as the high-entropy alloys of GdTbDyHoSc and GdTbDyHoY composition.