Enhanced corrosion resistance of Ti6Al4V with Ti-O film deposited by DC metal vacuum arc deposition

Ti-6Al-4V is widely used for fabricating biomedical implants because of their excellent mechanical performance, comparatively high corrosion resistance and good biocompatibility. However, there is increasing evidence that titanium metal ions may be released in vivo, and under certain conditions, extensively accumulated in adjacent tissue. Therefore, various modern modification methods are expected to enhance the corrosion resistance as well as the biocompatibility of these alloys. Among them, DC Metal Arc Deposition provides an attractive method owing to its high efficiency, easy control of composition and structure of the films, high adhesion force between film and its substrate. TiO films with different composition and structure as determined by XPS and XRD, were fabricated using DC Metal Vacuum Arc Deposition on a substrate of Ti-6Al-4V alloy. Various deposited TiO films with different O/Ti ratios were investigated by electrochemical tests in Hanks solution, which is commonly used for biomaterial evaluation. The open-circuit potential versus exposure time (I-t), polarization curves (E-I) and electrochemical impedance spectroscopy (EIS) of Ti-O film deposited samples in Hanks, were obtained with uncoated Ti6Al4V and heat oxidized TiO/sub 2/ film for comparison SEM observation and X-ray Spectrum Analysis were performed to investigate samples after polarization tests. The results show that Ti-O films enhance the corrosion resistance of the substrate materials greatly. I-t as well as E-I curves show that all the Ti-O film samples have lower dissolution current than the uncoated base materials, and the Ti-O film with highest O/Ti ratio present the best corrosion resistance behavior. EIS analysis indicates that Ti-O films have higher corrosion resistance owing to a barrier-type dense film layer which thereby slows the mass transport across the film to the substrate, and also due to its higher corrosion potential (E/sub corr/) than that of the uncoated Ti-6Al-4V. Ti-O - eposited samples possess higher corrosion resistance than heat oxidized TiO/sub 2/ films, this is attributed to a much denser film, since the DC Metal Vacuum Arc Deposition can provide denser refined films which further impede efficiently the transport of corrosion solution to the metal substrate.