Comparative Electrochemical Noise Characterization of Ti-CP2, Ti-6Al-2Sn-4Zr-2Mo, and Ti-6Al-4V in Ringer’s Solution Using Statistical and Hilbert–Huang Analyses

Titanium and its alloys are widely used in biomedical applications because of their favorable mechanical properties, biocompatibility, and corrosion resistance. This study comparatively evaluated the electrochemical behavior of Ti-CP2, Ti-6Al-2Sn-4Zr-2Mo, and Ti-6Al-4V in Ringer’s solution using electrochemical noise (EN), empirical mode decomposition (EMD), Hilbert–Huang Transform (HHT), and scanning electron microscope/Energy-dispersive X-ray spectroscopy (EDS) SEM/EDS characterization. Statistical EN analysis revealed marked differences among the investigated materials. Ti-6Al-2Sn-4Zr-2Mo exhibited the highest noise resistance (45,412 ± 57 Ω·cm2), followed by Ti-6Al-4V (11,784 ± 39 Ω·cm2) and Ti-CP2 (4114 ± 45 Ω·cm2), whereas relatively low localization index values were obtained for all three materials (0.02634–0.06). EMD revealed four, five, and six intrinsic mode functions for Ti-CP2, Ti-6Al-2Sn-4Zr-2Mo, and Ti-6Al-4V, respectively. Hilbert time–frequency–amplitude analysis further demonstrated distinct temporal and frequency distributions of the electrochemical fluctuations, with Ti-6Al-4V exhibiting the broadest and most persistent distribution of transient activity. SEM/EDS revealed localized post-exposure compositional heterogeneity and different degrees of accumulation of electrolyte-derived species but was not interpreted as direct evidence of passive-film chemistry or integrity. Overall, the combined statistical EN, EMD, Hilbert time–frequency, and SEM/EDS results demonstrate distinct passive electrochemical responses among the three titanium materials, with Ti-6Al-2Sn-4Zr-2Mo exhibiting the highest resistance to electrochemical fluctuations under the investigated conditions.