To overcome this issue, an increasing number of studies have focused on surface duplex treatment, especially on the grain refinement process followed by thermochemical treatment. However, being restricted by the reaction kinetics, the pursuit of a thicker ODZ generated by the method of increasing temperature or prolonging reaction time was not practical 10. Compared with thermal oxidation treatment, the OBD treatment can effectively improve surface hardness and wear resistance due to the generation of the thick oxygen diffusion zone (ODZ) 9. The OBD treatment embraces two steps: (1) thermal oxidation in air to form an oxygen reservoir, and (2) oxygen diffusion treatment of pre-oxidized samples in vacuum. To get better surface properties, a technique for obtaining higher surface hardness named oxygen boost diffusion (OBD) treatment has been proposed by Dong et al. Among the existing methods, surface thermo-chemical methods, including nitriding 3, carburizing 4, boriding 5, and oxidizing 6, 7, have been developed for improving the surface hardness and wear resistance.

Various surface modification methods have been applied to enhance the surface properties and fatigue resistance of titanium and its alloys 2. However, because of the poor fatigue resistance and tribological properties, the application of titanium is restricted 1. Titanium and its alloys have the advantages of low density, good corrosion resistance, and excellent machinability 1.

Stainless steel titanium mod