Tribological Behavior of Thermally Oxidized TC4 Titanium Alloy under Lubrication of a Full Formulated Engine Oil

The TiO₂ oxide film was prepared on the surface of TC4 titanium alloy by thermal oxidation treatment to improve the tribological properties under oil lubrication condition. The results was helpful to accumulate research data for the practical application of TC4 titanium alloy. In this work, the TC4 titanium alloy was thermally oxidized at 700 ℃ for 5 h in the air with a muffle furnace. The composition and structure of thermally oxidized TC4 titanium alloy was analyzed by X-ray diffraction, Raman and glow discharge spectrometry. The tribological properties of untreated and thermal oxidized treated TC4 titanium alloy was investigated under oil lubrication by UMT-3 at the loads of 10 N and 80 N. After test, the surface topography of wear tracks was observed by scanning electron microscopy and surface profiler instrument and composition was analyzed by X-ray photoelectron spectrometer. The friction-reducing and anti-wear mechanism was discussed. A dual-layer structure with an oxide layer on top of surface and an oxygen diffusion zone in the subsurface was fabricated on TC4 substrate after thermal oxidation treatment. As comparing with untreated TC4 samples, treated TC4 ones showed excellent tribological properties. In specific, the friction coefficients and wear rates of treated TC4 alloy were reduced. The rutile TiO₂ on TC4 titanium alloy after thermally oxidized treatment increased surface hardness, improved the wettability and induced the formation of phosphate-containing tribofilm during rubbing process. Hence, the tribological performance was improved.