Corrosion susceptibility of 316L stainless steel coated with titanium/titanium oxide to be used as biomaterial

摘要

316L stainless steel is one of the most frequently used materials in biomedical applications due to its good mechanical properties, corrosion resistance and biocompatibility. It is less expensive than titanium but it is non-osteointegrable. For that reason, it is of interest to develop a coating of some osteointegrable material so that to keep the good properties of the substrate and induce the osteointegration. Titanium dioxide is one of the most widely used materials for thin films due to its outstanding physical and chemical properties, which turn it suitable fora great variety of applications. Anatase, brookite and rutile are the three well-known crystalline phases of the TiO_2, rutile presenting higher biocompatibility and hemocompatibility. Then, rutile coatings on stainless steel have become a very attractive option for biomaterial applications. In this context, bilayer coatings of titanium-titanium oxide were developed over a substrate of 316L stainless steel, having been the titanium interlayers inserted in order to promote the growth of rutile. In this work, TiO_2 films were deposited on 316L stainless steel substrates employing a vacuum arc with a Ti cathode and the vacuum chamber acting as anode. The discharge was run at a 100 A current and 3×10~_(-2) mbar oxygen working pressure. The substrate was heated at 300 and 400 °C and biased at -120 V respect to the anode. The thicknesses of the titanium coatings were 50 and 100 nm, while the total thickness of the titanium oxide was 1000 nm. The objective of the present work was to evaluate the corrosion susceptibility of the materials with the above mentioned coatings in comparison with the susceptibility of the substrate (316L). To that purpose, the electrochemical behaviour of the materials under study was evaluated by drawing potentiodynamic polarization curves in a solution that simulates biological media. It was found that the substrate as well as most of the coatings are susceptible to pitting attack. However, the breakdown potential is lower for the substrate, indicating that this is the most susceptible material to that type of localized attack. On the other hand, the coatings with a titanium interlayer of 100 nm have shown the best response from the corrosion point of view. In particular, one of the specimens so obtained was immune to pitting, becoming the best alternative as biomaterial.