Effect of Applied Voltage on the Microstructure and Bioactivity of MAO Film on Ti Substrate

Various MAO films were prepared on Ti–6Al–4V substrate at voltages from 300 to 550 V in an electrolyte containing 0.18 M calcium acetate and 0.1 M sodium dihydrogen phosphate using an AC mode. Microstructures and phases of the MAO films were investigated by SEM with EDS and XRD. Bioactivity was examined using an apatite formation test in a simulated body fluid. The results show that the applied voltage has a significant influence on the microstructure and composition. With the increase in the applied voltage the sizes of micropores increase, and Ca P contents and Ca/P ratio in the MAO film increase too. And the Ca P contents in this work are increased obviously compared to DC MAO mode. The MAO films contain rutile, anatase and amorphous calcium phosphate, and higher voltage is favorable to form rutile phase. The results of the apatite formation test show that the AC MAO films exhibit higher ability to form apatite than DC mode. It is suggested that the AC MAO mode is more effective to incorporate calcium and phosphorous in the oxide layer than DC mode because higher applied voltages can be applied in it, and the AC MAO film present a better performance in the formation of calcium phosphate which may be result from a more effective release of CaP from MAO film into SBF.