Effect of thermal oxidation conditions on tribological behaviour of titanium films on 316L stainless steel

A novel surface coating technique has been developed in the present work to enhance the tribological properties of AISI 316L stainless steel. The technique involves the deposition of a titanium film onto AISI 316L stainless steel by magnetron sputtering and then thermal oxidation to partially convert the titanium film to titanium oxide. The resultant film has a layered structure, comprising of a rutile titanium dioxide (TiO2) layer at the top, an oxygen- and nitrogen-dissolved α-Ti layer in the middle and a diffuse-type interfacial region. Such a hybrid film system has good adhesion with the substrate, can significantly enhance the surface hardness and tribological properties of the stainless steel in terms of much reduced friction coefficient and increased wear resistance. However, the tribological behaviour of the oxidised film system is significantly affected by the oxidation condition, mainly temperature and time. Detailed studies on the response of the titanium film to thermal oxidation at temperatures between 500 and 700 °C showed that oxidation at low temperatures, i.e., 500 and 550 °C, can offer much better tribological enhancement than high-temperature oxidation.