Microstructural and functional evaluation of bioactive glass–ferrite hybrid coatings deposited on pure titanium using an electric-field-assisted technique

In this study, bioactive glass-ferrite (Fe₃O₄) hybrid coatings were deposited on commercially pure titanium using an electric-field-assisted electrophoretic deposition (EPD) technique, and their microstructural and functional properties were quantitatively evaluated. Bioactive glass co-deposited with 5 wt.% Fe₃O₄ particles at a constant applied voltage of 25 V, while the deposition time was systematically varied between 6- and 24-min. Microstructural observations revealed that short deposition times (6-12 min) resulted in discontinuous and non-uniform coatings, whereas prolonged deposition (18-24 min) produced dense, continuous, and well-adhered layers. Wettability measurements showed a pronounced enhancement in surface hydrophilicity, with water contact angles decreasing from 57.6 ± 1.22° for the bare substrate to 35.4 ± 1.35° and 18.9 ± 1.18° for coatings deposited for 12 and 24 min, respectively. Electrochemical tests in phosphate-buffered saline at 37 °C demonstrated that increasing deposition time improved the barrier performance of the coatings, as evidenced by a reduction in corrosion current density from 8.16 × 10⁻⁷ A/cm² at 18 min to 2.95 × 10⁻⁷ A/cm² at 24 min, alongside an increase in charge transfer resistance from 1.35 × 10⁴ to 4.58 × 10⁴ Ω·cm². Although the uncoated titanium exhibited the highest intrinsic corrosion resistance due to its stable passive oxide layer, the optimized hybrid coating deposited at 25 V for 24 min offered the best compromise between enhanced surface roughness, superior wettability, and improved electrochemical performance among the coated samples.