OBJECTIVETo explore the effect of changes of processing time on the surface properties of titanium coating formed by micro-arc oxidation (MAO).

METHODSForty-four disc-shaped pure titanium specimens with 10 mm diameter and 1 mm thickness were equally divided into 4 groups and processed by MAO technique in electrolytes containing 0.2 mol/L calcium acetate (CA) and 0.02 mol/L β-glycerol phosphate disodium salt pentahydrate (β-GP). The processing time were set at 1 min, 5 min, 10 min and 15 min respectively. The topograph of the MAO film surface and the film-substrate interface was observed by a scanning electron microscopy (SEM), and the composition was analyzed by an energy dispersive spectroscope (EDS) incorporated in the SEM. The phase and the microstructure of the film were analyzed by X-ray diffraction (XRD). The roughness of the film was measured using a roughness tester. The surface static contact angle was detected by a contact angle measurement instrument and the surface energy was calculated accordingly.

RESULTSWith the increase of processing time from 1 min to 15 min, the pore size increased from (1.30 ± 0.07) µm to (1.55 ± 0.09) µm, and film thickness increased from (10.2 ± 1.1) µm to (20.9 ± 2.9) µm. The content of the Ca in the film increased accordingly, and Ca/P increased from 1.99 to 2.45, and the surface energy increased from 24.62 mJ/m(2) to 39.49 mJ/m(2). Meanwhile, the XRD pattern indicated that rutile increased but anatase and titanium decreased gradually. At the time of 15 min, part of the MAO film peeled off.

CONCLUSIONSProcessing time has impact on the thickness, surface topography, crystal component and surface energy of titanium MAO coating. MAO film treated for 5 - 10 min demonstrated favorable surface properties.