Effects of processing time on the structural characteristics of microarc oxide coating on the surface of pure titanium

A porous composite oxidation coating with calcium and phosphate was prepared on pure titanium surface by a microarc oxidation technology. Effect of processing time on the topography, thickness, composition and structure of the oxidation coating was investigated via scanning electron microscope, X-ray diffractometer and electron probe microanalysis method. The results indicate that the thickness, micropore quantity, and micropore size of the coating increase with increasing processing time, and the pore size distribution becomes narrower when the processing time increases. The deposition of calcium phosphate salt on the sample surface gradually decreased and finally disappeared, but the mole ratio of calcium to phosphorus became stable with increasing the processing time. The increase of processing time resulted in the increased rutile phase and the decreased anatase phase in the coating. The microarc oxidation process of pure titanium surface could be classified into the four stages, i.e., ordinary anodic oxidation, microarc discharge, microarc oxidation and microarc quenching. The formation of porous oxidation coating was composed of the coating formation, micropore formation, micropore growth and micropore fusion.