This work investigates four different oxidation processes to modify the surface of Ti6Al4V and the equimolar high entropy alloy TiZrNbHfTa. The aim is to generate hard, adherent oxide layers with an underlying pronounced oxygen diffusion zone exhibiting a gradual hardness decrease. This can positively affect the tribological behavior of both alloy systems and, in particular, improve their wear resistance. The studied oxidation processes are: a single-step process consisting of oxidation in air, a two-step process in which oxidation in air is followed by an oxide reduction under vacuum, a three-step process in which the oxide reduction is followed by another oxidation step, and an oxidation process at reduced oxygen partial pressure.