Titanium alloys (Ti6Al4V) are extensively used in medical implants due to their biocompatibility and mechanical strength, yet long-term corrosion in physiological environments remains a challenge. This study evaluates the corrosion resistance of nanostructured hydroxyapatite (HA), HA-selenium (HA-Se), and HA-selenium-collagen (HA-Se-Col) coatings on Ti6Al4V via electrochemical deposition. Electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF) revealed distinct corrosion mechanisms, that the HA coating reduced corrosion resistance by 35–40% compared to uncoated Ti6Al4V after 1-hour immersion due to high porosity (20–25%), enabling rapid electrolyte penetration. HA-Se exhibited comparable corrosion resistance to uncoated alloy, indicating selenium alone minimally enhances protection. In contrast, HA-Se-Col demonstrated a 60–65% improvement in corrosion resistance, attributed to collagen’s pore-filling effect (reducing porosity to 8–10%) and formation of a stable protective layer. Nyquist plots showed HA-Se-Col’s charge transfer resistance (25–30 kΩ·cm²) surpassed HA (8–10 kΩ·cm²) and HA-Se, while Bode-phase analysis revealed HA’s three time constants (linked to solution resistance, coating defects, and charge transfer) simplified to two in HA-Se-Col, reflecting structural homogeneity. These findings demonstrate that collagen synergizes with selenium to optimize HA coatings, offering enhanced corrosion resistance for biomedical implants through microstructural refinement and electrochemical stabilization.
