Atomic Layer Deposition as an Alternative Surface Finishing Technique: Characterisation of Oxide Layer Composition and Corrosion Behaviour

Nitinol is an important material for medical implants due to its super elastic behaviour and since its mechanical properties mimic biological materials. The surface of nitinol implants is commonly covered with a thin titanium dioxide (TiO₂) layer which acts both as a passivating layer to increase the corrosion resistance and as a barrier layer to address the toxicological concerns of long-term nickel release into the biological tissue. Even though nitinol undergoes a natural passivation when exposed to air, various thermal, chemical, and electrochemical surface finishing techniques are applied during manufacturing to replace the native oxide layer by uniform TiO₂ layers of controlled thickness. The properties of these oxide layers depend on the surface finishing technique and the process parameters.