Effect of TiO₂ Nanoparticle Addition on the Tribological Properties of CNT Coatings

Carbon nanotube (CNT) coatings show excellent tribological properties but face challenges in dispersion and industrial application. This study investigated TiO₂ nanoparticle incorporation effects on CNT coating tribological performance. CNT/TiO₂ composite coatings with varying TiO₂ content (0.5-2.0 wt.%) were fabricated on SUS 304 substrates via spin coating. Surface morphology, roughness, wettability, and tribological properties were characterized using confocal microscopy, SEM, Raman spectroscopy, and reciprocating friction tests. Results showed that low TiO₂ concentrations (0.5-0.7 wt.%) achieved optimal performance. The C3-Ti0.5 specimen maintained substrate-level smoothness (Ra = 0.09 μm) while preserving coating integrity. Raman analysis confirmed structural preservation of CNTs (ID/IG ≈ 1.0) across all formulations. Tribologically, C3-Ti0.5 exhibited a friction coefficient of 0.099, approaching pure CNT coating performance (0.090), with a wear rate of 9.00 × 10^-7 mm³/N·mm. Higher TiO₂ concentrations progressively degraded performance, with C3-Ti2 showing increased friction (0.263) and wear rate (2.87 × 10^-6 mm³/N·mm). The 0.5-0.7 wt.% TiO₂ range represents optimal composition for applications requiring both smooth surface finish and superior tribological performance, particularly for precision mechanical components where surface quality and friction control are equally critical.