Corrosion behavior of TiO2 films on Mg–Zn alloy in simulated body fluid

Magnesium alloys have been widely investigated in the field of biomaterials due to their moderate mechanical properties close to human bone and gradual degradation in human physiological environment without second surgeries. But results from clinical studies showed that magnesium implants suffered from too rapid degradation in human physiological environment. To reduce the degradation rate of magnesium alloys, surface modification is essential and effective besides element alloying. In this study, TiO2 films were deposited on Mg–Zn alloy by direct current reactive magnetron sputtering. The morphology and structure of the films were characterized by atomic force microscopy (AFM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The corrosion resistance in simulated body fluid (SBF) at 37 °C was evaluated by potentiodynamic polarization and hydrogen evolution tests. The corrosion behavior of the samples was investigated by SEM with energy dispersive spectroscopy (EDS) after immersion for different periods. The results showed that the compact films were composed of particles with the size of about 100 nm and could effectively improve the corrosion resistance in SBF. After immersion for 10 days, the corrosion rates of the substrates and samples with TiO2 films were 4.13 mm/y and 1.95 mm/y, respectively. During the immersion, the TiO2 films could induce the growth of hydroxyapatite (HAp) to improve the bioactivity of the samples.