Different tribological behaviors of titanium alloys modified by thermal oxidation and spraying diamond like carbon

• A thickness of 10 μm oxide coating formed by new thermal oxidation process.
• A thickness of 3 μm DLC coating with Cr and W–DLC transition layer formed.
• Micro-hardness increased while friction coefficients decreased significantly.
• Wear volumes decreased by 70% for thermal oxidization while by 95% for DLC at most.
• DLC is more promising than oxidization to improve the bio-tribological properties.

The tribological behaviors of titanium alloys modified by new thermal oxidation and spraying diamond like carbon (DLC) were compared with original sample. The structural characteristics, micro-hardness, friction and wear properties in dry fiction and bovine serum lubrication were investigated. According to the results, rutile TiO2 as well as alumina and DLC coating formed with the micro-hardness increasing by 1.27 and 2.21 times separately after being treated by thermal oxidation and spraying DLC, respectively. After modification, the average friction coefficients with a counterface of ZrO2 ball decreased significantly, especially under spraying DLC treatment. After wear test, the wear volumes in dry sliding condition decreased by 37.6% under thermal oxidation and decreased by 94.8% under spraying DLC treatment, respectively. In 25% bovine serum lubrication and compared with the original sample, wear volumes decreased by 70.7% under thermal oxidation and decreased by 93.8% under spraying DLC treatment, respectively. The surface ploughing by the hard mating ball mainly affected the friction and wear of untreated samples. The predominant factor for oxidized samples was the mechanical interaction between two hard ceramic surfaces: (TiO2/Al2O3) and ZrO2 while the improvement of friction and wear resistance for DLC coating was attributed to the decrease of the shearing forces. In this investigation, the results proved that spraying DLC was more promising than thermal oxidation to improve the tribological properties.