Assessment of the Corrosion and Tribological Properties of Double Layer Nitride Coatings Performed by Plasma Nitriding and Cathodic Arc Evaporation on Ti-6Al-4V Alloy

High corrosion resistance, proper mechanical properties, and biocompatibility of Ti-6Al-4V alloy make it suitable for medical (dentistry and orthopedic implants), military and electronic industries. The greatest disadvantages of this alloy are poor wear resistance, low fatigue strength and poor tribological properties. The aim of this study was to apply an adhesive coating to improve both corrosion and wear properties of the Ti-6Al-4V alloy. Surface modification of alloy was done by nitrogen plasma nitriding in both electrolyte plasma and atmosphere plasma environment. Finally, the TiN layer was coated on the modified samples, using cathodic arc evaporation technique. The microstructural investigation, surface morphology, and coating thickness were studied by field emission scanning electron microscope (FESEM) equipped with energy dispersive spectroscopy. The grazing incidence X-ray diffraction (GIXRD) was applied to study the phases in the coatings. The corrosion resistance was studied with potentiodynamic polarization and electrochemical impedance spectroscopy. The wear resistance and the coating coefficient of friction were tested with pin-on-disc machine. The corrosion resistance of the samples was improved by applying the coatings and the plasma-nitride/TiN double-layer coating showed the best corrosion resistance with current density of 1.46×10-7A/cm2 and corrosion potential of -0.3V. On the other hand, the lowest thickness reduction in wear test was observed in double-layer coatings, so that the thickness reduction for both double-layer coatings, was less than 4μm, after 300m sliding.