The Effect Of Process Parameters On The Thickness, Bond Strength And Bioactivity Of The Titanium Micro-arc Oxidation Film

Pure titanium and titanium alloy most widely applies for clinical implant materials at present.The surface modification of titanium and titanium alloy by Micro-arc Oxidation(MAO) is very important for titanium and titanium alloy to improve its biological activity,bond strength and binding between the implant and the bone tissue.The titania film and titania/titanium composite materials on the titanium based materials surface were prepared by using the micro-arc oxidation(MAO) method.The effects of the MAO process parameters on the morphology,phase composition,element contents and bond strength between the film and titania substrate were systematically studied in this paper.Meanwhile the different effects on the film between the acidic electrolyte and alkaline electrolyte were researched,the bioactivity was also studied by means of simulated body fluid(SBF) immersion test.The results showed that the morphology,lattice type and the quantity of the Ca and P in the films can be changed by changing the voltage,frequency,reaction time,duty-cycle and pH value of the electrolyte.The micro-pores were found in the oxide films.The size of the pores and the surface roughness of the film can be increased by raising the reaction time and the anode voltage, but the change trend of the density of the pores was opposite.(1) Under the constant voltage mode,the thickness of the film was improved by increasing the voltage,reaction time and dutycycle, but decreased by increasing the frequency.The effect of increasing the voltage and the reaction time was more obviously,but the increasing the duty-cycle was not obviously.The factor of effect on the film thickness,according to the primary-secondary order is:Final voltage＞time＞duty-cycle＞frequency.(2)The bond strength between the TiO₂ film and the substrate was improved by increasing the voltage and decreased by increasing the reaction time under a shot reaction time.(3)Treated titanium with MAO in the electrolyte containing Ca and P can put these elements into the oxide film and the bioactivity of the porous TiO₂ film was improved.The Ca/P ratio in the film which was treated by MAO in the alkaline electrolyte was more approach to the human hard tissue.The thicker film which also had the better bioactivity was acquired when treated in alkaline electrolyte.The better bond strength was realized in acidic electrolyte than in alkaline electrolyte.The titania/titanium composite materials prepared by MAO have good bioactivity and mechanical properties.The thickness of the film when treated by MAO under the voltages from 350V to 450V in the acidic electrolyte is from 4.3μm to 11.1μm.And the nominal bond strength (tensile strength) between the film and substrate is more than 31.58MPa.The actual bond strength is more than 52.63MPa when the porosity is 40%.The thickness of the film is 12.3μm when treated by MAO under the voltage 450V in the alkaline electrolyte.And the nominal bond strength between the film and substrate is 30.92MPa.The actual bond strength is 51.53MPa when the porosity is 40%.