Surface modification of a Ti6Al4V alloy by thermal oxidation to improve its tribological properties

•Effect of thermal oxidation on crystal growth on the surface of a Ti6Al4V alloy.•The increase in hardness favors the improvement of tribological properties.•The transformation caused by the heat treatment is reflected on the surface and in its crystalline structure. The purpose of this research is to evaluate the effect of thermal oxidation on the surface of a Ti6Al4V alloy in terms of increasing hardness and improving its tribological values. A two-hour heat treatment was carried out at the following temperatures: 450 °C (TT450), 550 °C (TT550), 650 °C (TT650), 750 °C (TT750) and 1000 °C (TT1000). Starting with sample TT650 significant changes occurred in the alloy morphology that identified the formation of the rutile crystal phase. At 750 °C, a maximum hardness of 13.98 GPa was achieved, with an improvement over the alloy without heat treatment. By increasing the temperature, the wear rate was reduced to 2.26E−5 mm3/Nm at 750 °C and the friction resistance oscillated around 0.58. The heat treatment at 750 °C improved the tribological properties and favored a higher hardness of the alloy due to the formation of the rutile phase and to morphological changes.