Wear resistance of smooth TiO2 coating obtained by anodic oxidation and sol-gel dip-coating combination

This study investigates the wear behavior of crystalline TiO₂ coatings on Ti-6Al-4V substrates: a sol-gel only film (TSS; thickness ∼ 90 nm) and a combined anodic-oxidation and sol-gel system (TASS; thickness ∼ 600 nm). Wear tests employed reciprocating ball-on-flat apparatus with a conical diamond counterface (hemispherical tip radius 10 µm) to replicate prosthetic-valve leaflet motion under dry, unlubricated conditions at service-like or higher sliding speeds and contact pressures (∼10 000 MPa). Tests were run at loads of 39, 78, 117 and 156 mN for 1–4 min. Wear scars and debris were examined qualitatively, while wear volume, wear rate and wear factor were quantified with statistical analysis and uncertainty propagation. At the lowest loads (39 and 78 mN), both TSS and TASS outperformed the bare Ti-6Al-4V, exhibiting significantly lower wear volumes. At 117 mN, TSS exhibited the highest wear volumes—attributed to abrasive TiO₂ debris—whereas TASS remained comparable to the bare alloy; at 156 mN, TASS maintained lower wear than TSS and matched the substrate. Coatings that did not fail—i.e., did not expose the Ti-6Al-4V surface—showed wear factors of 2 × 10 − 4 to 3 × 10 − 4 m m 3 N − 1 m ⁻ ¹ , consistent with literature. Wear-rate maps, created separately for bare Ti-6Al-4V, TSS and TASS by fitting wear rate versus load and time, illustrate each system’s load-time response and reveal that TASS extends the low-wear regime relative to TSS. These maps offer a predictive framework for optimizing coating design in durable biomedical devices. • Smooth TiO 2 coatings of 100 and 600 nm thicknesses were obtained on Ti-6Al-4V. • Ball-on-flat tests were performed with loads ranging from 39 to 156 mN for 1–4 min. • The thickest coating showed the highest wear resistance. • The wear increased linearly over time but increased suddenly when the coating failed. • TiO 2 debris accelerated the wear after the coating failed.