Effect of micro-arc oxidation time and applied voltage on formation of strontium- and silicon-incorporated biocoatings

The study of the influence of the MAO time and applied voltage on the formation of the structure, phase and elemental compositions, and properties of Sr-Si-CaP coatings on the titanium surface were performed. It was established that the coating thickness, roughness and the average size of the structural elements (spheres and pores) grow linearly with increasing of the MAO voltage from 200 to 370 V. While, the MAO time effects only on the coating thickness. XRD revealed that the coatings deposited at the low voltages of 200-250 V have X-ray amorphous structure. Increase of the voltage to 350 V leads to the formation in the coatings of crystalline-amorphous structure with amount of crystalline monetite (CaHPO4) phase to 35±5 wt.%. The EDX microanalysis showed that maximum Ca/P atomic ratio of 0.9 and maximum contents of 1.0 at.% Sr and 1.2 at.% Si were found on the coating surface in the regions of accumulation of the monetite crystals for the coatings deposited at high voltages of 300-350 V.