Characterisation of the nanotubular oxide layer formed on the ultrafine-grained titanium

Commercially pure titanium (cpTi) and titanium alloys are metallic implant materials usually used in dentistry and orthopaedics.  In order to improve implant properties, Ti-based materials may be surface modified by different procedures. One of the most attractive methods is electrochemical anodization, as a method for obtaining nanotubular oxide layer on the material surface, aiming at improving mechanical, biological and corrosion properties of the metallic biomaterials. In the present study, ultrafine-grained titanium (UFG cpTi) was obtained by high pressure torsion (HPT) under a pressure of 4.1 GPa with a rotational speed of 0.2 rpm, up to 5 rotations at room temperature. In order to form homogeneous nanotubular oxide layer on the UFG cpTi, the electrochemical anodization was performed in phosphoric acid containing 0.5 wt. % of NaF electrolyte during anodizing times of 30, 60 and 90 minutes. The characterisation of thus formed nanotubes was performed using the scanning electron microscopy (SEM), while the surface topography was analysed using the atomic force microscopy (AFM). The results show that the electrochemical anodization process leads to an enhanced roughness of the surface. The mechanical behaviour of the UFG cpTi after the electrochemical anodization process is estimated using the nanoindentation technique. Obtained results show that anodized material has lower value of nanohardness than non-anodized material. Moreover, anodized UFG cpTi has lower modulus of elasticity than non-anodized UFG cpTi and the value is close to those observed in bones