Fatigue behavior of modified surface of Ti–6Al–7Nb and CP-Ti by micro-arc oxidation

•Growth of protective oxide on biocompatible metals by electrochemical technique.•Influence of micro-arc oxidation on the fatigue properties.•Fatigue behavior with anodization is similar to unmodified surface.•Typical fatigue initiation indicates the absence of any apparent damage.

The influence of micro-arc oxidation (MAO) process on the fatigue properties of Ti–6Al–7Nb and commercially pure Ti (CP-Ti) was investigated. Polished and anodized specimens of both materials were tested in axial fatigue to obtain S–N curves and the oxide layer was characterized to support the comparison among the fatigue properties resulting from the different surface conditions. The MAO procedure led to the formation of highly porous oxides, with a uniform distribution of pores; oxide films consisted of anatase TiO2 and were free of Al or any other alloying elements. These morphology, structure and composition are desirable on the surface coating for favoring the implantation by increasing the bonding characteristics between the implant and the bone. Fatigue behavior was not modified by the MAO process in both Ti–6Al–7Nb and CP-Ti when compared to the samples without surface modification. The nano-thickness and double-layer structure of the oxide formed on the MAO process, with an inner compact structure free of defects, as well as the surface compressive residual stresses typically produced by the anatase phase, ascribe the unaffected fatigue performance, rendering the materials in this condition suitable characteristics in designing orthopedic implants.