Mechanical properties of anodically oxidized cpTi and Ti-6Al-7Nb alloy

Surface modification techniques play an important role in tailoring physical and chemical properties of titanium and its alloys, as well as in adjusting their biocompatibility. In order to reduce the penetration of alloy element ions into the organism, an anodising process is used that creates an oxide layer on the surface of the implant that protects it from a corrosive environment. The other important issue related to the generation of surface films is providing the proper set of mechanical properties. Therefore, this study involves tests of the mechanical properties of layers formed using anodic oxidation on the surface of test pieces from Grade 4 titanium and Ti-6Al-7Nb titanium alloys. The anodising was performed with an electrolyte based on phosphoric and sulphuric acid under potentials in the range of 40–100 V. In order to assess the mechanical properties of layers generated using this method, the hardness tests and tests of these layers’ adhesion to the metal base were performed. The Oliver Pharr method was used to measure the instrumental hardness, while the scratch test was performed to study the layers adhesion to the surface. The measure of the strength of layer adhesion to the base is a critical force, i.e. the minimum normal force that causes the loss of adhesion to the surface. The obtained data showed different mechanical properties of anodic films generated under different potentials in the anodizing process. The knowledge gained from this research has practical importance for the application of such surface treatments for various types of implants used in the human cardiovascular system.