Growth Mechanisms and Tribocorrosion Behavior of Bio-Functionalized ZrO2 Nanoparticles-Containing MAO Coatings Formed on Ti-40Nb Alloy

Tribocorrosion resistance, low elastic modulus, and faster promotion of osseointegration are among the current requirements to avoid aseptic loosening in artificial joints. Therefore, in this work, a promising orthopedic Ti-40Nb alloy was used and its surface was modified by micro-arc oxidation (MAO), resulting in a multi-scale porous surface incorporated with multiple bioactive species (Ca, P, Mg, Zn, and Sr) and ZrO2 nanoparticles (ZrO2 NPs). The effect of different processing voltages is discussed on the formation mechanisms of the coatings and incorporation of ZrO2 NPs. The resulting tribocorrosion behavior is elucidated for two loading conditions in phosphate-buffered saline (PBS) solution. Similar growth mechanisms were observed for all films, resulting in a triplex structure (barrier film, inner porous layer, and outer porous layer). However, higher processing voltage produced thicker anodic films with smaller average surface porosity and increased rutile content. Higher voltage also resulted in higher amounts of ZrO2 NPs in the coating. A mechanism is proposed to explain the incorporation of NPs, based on the combined effect of electrophoresis and strong micro-arcs and discharges originated during MAO treatment. That enhanced incorporation of ZrO2 NPs may retard eventual phenomena of cracking associated with harder materials (rutile) under vigorous mechanical solicitations.