Effect of Gas Nitriding on Morphology and Wear Resistance of TiO2 Coatings Formed by Electrolytic Plasma Oxidation

In this study, two processes of plasma electrolytic oxidation coating and gas nitriding have been investigated. In the first step, titanium oxide was coated by plasma electrolytic oxidation method in carbonate solution with current density of 1000 mA/cm2 for 10 min to form the first layer on the titanium substrate. In the second step, the second layer was formed by gas nitriding. Nitriding carried out in a tube furnace at 1000℃ for 6 hours on TiO2 coated titanium. The wear test, X-ray diffraction and scanning electron microscopy were performed on different coatings for determination of the properties. The results showed that, the initial coating mostly contains rutile. The morphology and the structure of the coating showed the presence of micro-cavities. Based on wear test results, the electrolytic plasma oxidation process, provides an ideal annealing condition with low friction coefficient of 0.2. For the nitrided coating, some titanium oxides converted into nitrated phases. The tribological study showed that the wear resistance of nitrided titanium oxide increased significantly compared to titanium oxide coatings and uncoated samples which is, the friction coefficient from 0.65 for the uncoated sample decreased to 0.25 for the nitrided titanium oxide sample.