Sliding wear resistance of oxide layers formed on a titanium surface during thermal oxidation

Titanium and its alloys are widely used in engineering and biomedical applications. These materials manifest a unique combination of mechanical properties, exceptional corrosion resistance and good biocompatibility. The main drawback of these materials, however, consists in their poor tribological properties, which can be significantly improved by using isothermal oxidation. The objective of the paper was to examine the impact of the oxidation temperature on the morphology, hardness and tribological properties of oxide layers formed on the surface of titanium. The oxidation process was conducted at temperatures of 600 and 700 °C over 72 h. The morphology of the scale formed was determined. It was found that after oxidation at a temperature of 600 °C an oxide layer covered the entire examined surface, but in certain areas unevenly. Finer and more agglomerated oxide particles formed after oxidation at 700 °C. The hardness of the obtained oxide layers was 4 times higher compared to the hardness of the titanium substrate. Tribological tests were performed on a commercial ball-on-disc wear tester under conditions of technically dry friction, at a load of 10 N. The friction distance was 1000 m. An aluminium oxide (Al2O3) ball was used as a counter-specimen. It was determined that the presence of the oxide layer on the surface of titanium significantly increased resistance to sliding wear. After oxidation of a titanium disc at 600 and 700 °C it was observed that its volumetric wear had decreased by 47 and 61%, respectively.