Study On The Preparation Of Titanium Micro-arc Bioceramic Coating

Titanium Alloy is widely used as implant material. Micro-arc oxidation is one of the surface processing methods which can improve alloy's biological activity and wear resistance. Nowadays, the study on titanium bioceramic coating prepared by MAO technology was carrying out gradually. The electrolyte with addition of calcium and phosphorus is the first choice through most study. However, the microscopic characteristics and performance of the MAO coatings is related to a large number of parameters. Therefore, a further study should be developed on the formation mechanism of MAO bioceramic coatings.Kinds of MAO bioceramic coatings were prepared under different parameters in this paper. Phase structure, element content and surface morphology of MAO coatings which were prepared under different Ca/P of the electrolyte were studied. The influence law of electrical parameters to the microscopic characteristics of MAO coatings were also analyzed in the paper. The formation mechanism of MAO coatings had hereby been developed. The influence law of the content of calcium and phosphorus in MAO coatings to the biological activity was studied by immersing the MAO sample in SBF solution for several days. And the wear resistance of coatings was analyzed through friction and wear test.The result shows that the MAO coatings were mainly composed by rutile and antase TiO₂. The relative content of rutile and antase was different under different parameters. The content of calcium in MAO coatings increased gradually while the content of phosphorus first decreasing then increasing as the Ca/P of the electrolyte was higher. And hydroxyapatite (HA) was formed on the coating as the Ca/P increased to a certain value.Porosity and content of Ca and P of the MAO ceramic coating were changing as the value of voltage, frequency or duty cycle was different. This is because the charge accumulation is influenced by the change of electrical parameters. As a result, the electric breakdown process of oxidation film shows with different features, thus kinds of ceramic coatings with different morphology and structure. Kinds of partials consist of the equivalent load which was paralleled by resistance and capacitance. The number of charge that flow through the equivalent resistance and accumulate on the equivalent capacitance was influenced by the electrical parameters, so that the electric field distribution in the solution is changing. The process of diffusion and electrophoresis of partials is therefore influenced, and the micro structure of the coating is different.After two weeks immersion in the SBF solution, the result shows that the higher content of Ca and P in MAO coating, the more HA phase were induced and formed on the surface of the coating. The MAO process improved the biological activities of titanium alloy. The friction and wear test shows that the wear resistance of the ceramic coating is much better than the titanium matrix. The wear rate increased while the wear resistance decreasing as the value of voltage, frequency or duty cycle is higher.