Investigation of the influence of deposition time on morphology, crystallographic texture, and corrosion resistance of ZnO coatings on titanium substrates

Abstract

This study examines the effect of deposition time on the microstructural evolution and functional performance of zinc oxide (ZnO) coatings on titanium substrates using electrophoretic deposition. Morphological analysis via scanning electron microscopy revealed a time-dependent transition from incomplete nucleation at 2.5 min, producing uneven flake-like structures, to a more uniform and compact coating at 5 min due to enhanced ion mobility and stable particle flux. With extended times (10–20 min), competitive crystal growth dominated, leading to coarse flakes with reduced packing density and increased interflake porosity. Crystallite size, determined using XRD and the Scherrer equation, increased from 34.1 nm to 62.4 nm with deposition time, reflecting enhanced crystal coalescence and orientation, particularly along the (0002) plane—a thermodynamically stable direction associated with improved corrosion resistance. Surface roughness peaked at 1.76 ± 0.39 μm for the 10-min sample, while coating thickness increased steadily from 4.56 ± 0.3 μm to 23.5 ± 0.4 μm. Wettability improved initially (contact angle 69.4° at 5 min) before declining due to morphological changes (contact angle 79.7° at 20 min). Electrochemical impedance spectroscopy and polarization tests identified the 5-min coating as optimal, exhibiting the lowest corrosion rate (2.103 ± 0.035 μm/year) and highest polarization resistance (2.06 × 10⁵ ± 0.56 × 10⁵ Ω·cm²) in PBS solution. These results demonstrate that deposition time fundamentally governs the nucleation–growth dynamics, microstructural texture, and electrochemical stability of ZnO coatings.