[Effects of film thickness on the phase composition and microstructure properties of micro-arc oxidation coating]

In this study, we obtained the TiO2 films with different thickness by micro-are oxidation (MAO) on commercially available pure titanium. By altering the duration time, we got the films 5 microm, 10 microm, and 20 microm in thickness, respectively. XRD and SEM were employed to characterize the phase, composition and microstructure of the films. The MAO film, which was about 5 microm thick, was porous and even with the pore size about 1 microm. No other crystalline phase except anatase was detected by XRD. The film, which was 10 microm thick, was similar to the former. The pores were well separated and homogeneously distributed over the surface. The XRD pattern indicated that the film was composed of anatase and a minor amount of rutile, whereas the pore size of 20 microm film was about 4-6 microm and was bigger than the others. Furthermore, the small cracks were easy to observe. XRD pattern showed that the Ti peak was significantly reduced and new Ca, P, O containing compound was formed in addition to rutile and anatase with the film thickness increasing. There were significant differences in regard to surface roughness of the three groups. These findings suggest that the film thickness has an intense effect on the quality of the MAO coating. By changing the film thickness, we can extensively change the composition, structure and chemical properties of the surface layer on titanium.