Repassivating tantalum/tantalum oxide surface modification on stainless steel implants

Medical implants that require ductility, high mechanical strength and endurance are commonly made of stainless steel (AISI 316L). Depending on environment and function steel surfaces may be attacked by pitting corrosion leading to post-operative complications. However, the electrochemical surface properties of austenitic steel can be modified for higher corrosion resistance. In this work, steel surfaces are coated with a sandwich layer of tantalum and tantalum oxide, using a PVD sputter process. Mechanical stability is tested and crack generation of the modified material is determined by a four-point bending test connected with a corrosion current measurement using physiological saline solution as the electrolyte. The mechanical stability and repassivation properties of the material are guaranteed up to the onset of substrate plastic deformation. While biocompatibility is obtained by tantalum oxide the ductility is achieved by the tantalum interface which at the same time ensures continued film adhesion, even after plastic deformation of the steel substrate.