Common methods to increase the wear resistance of titanium by surface hardening in biomedical applications, such as chemical/physical vapour deposition techniques or thermal/electrochemical oxidation, result in a layer of titanium dioxide or titanium nitride on the metal surface with a sharp interface between the hard and brittle coating and the ductile metallic substrate. A major disadvantage of these methods is that the sharp transition in material properties may cause exfoliation of these coatings. In this work, a two-step heat treatment was used to investigate oxygen diffusion hardening and its capability to produce hard surfaces with a transition zone between the coating and the ductile substrate. During the first step, the native oxide layer was strengthened. In the second step, oxygen diffusion was activated and a transition zone was formed. Different methods of analysis confirmed the success of the thermal treatment, as well as the change of the mechanical properties.