Corrosion and Wear Behavior of TiO 2 /TiN Duplex Coatings on Titanium by Plasma Electrolytic Oxidation and Gas Nitriding.

In this study, corrosion and wear behavior of three kinds of coatings by two processes, namely, plasma electrolytic oxidation (PEO) coatings (Ti/TiO 2 ), gas nitriding coating (Ti/TiN), and the duplex coating (Ti/TiO 2 -N) by combination of PEO and gas nitriding methods were systematically investigated. X-ray diffraction tests, field-emission scanning electron microscopy, and adhesion tests are employed for the coating characterization, along with the wear and electrochemical test for evaluating the corrosion and tribological properties. The morphology and structure of the coating consist of micro-cavities known as the pancake structure on the surface. The electrolytic plasma oxidation process produces a typical annealing behavior with a low friction coefficient based on the wear test. The coating consists of nitride and nitrate/oxides titanium for nitrided samples. The surface morphology of nitrided oxide titanium coating shows a slight change in the size of the crystals and the diameter of the cavities due to the influence of nitrogen in the titanium oxide coating. The tribological behavior of the coatings showed that the wear resistance of the duplex coating (Ti/TiO 2 -N) and Ti/TiO 2 coatings is significantly higher compared to Ti/TiN coatings and uncoated Ti samples. The polarization resistance of the Ti/TiO 2 -N and Ti/TiO 2 coatings was 632.2 and 1451.9 kΩ cm 2 , respectively. These values are considerably greater than that of the uncoated Ti (135.9 kΩ cm 2 ). Likewise, impedance showed that the Ti/TiO 2 -N and Ti/TiO 2 coatings demonstrate higher charge transfer resistance than that of other samples due to better insulating behavior and denser structure.