| In this thesis, the ceramic films on TC4 titanium alloy and TA2 pure titanium are prepared by industrial frequency power supply with a realtime data collecting system of electrical current and voltage made by National Key Laboratory Superhard Materials of Jilin University. The composition and structure of the coatings are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical microscopy. The constant voltage tester detects the anti-point corrosion property. During the experiments, the effects of the relative parameters on the growing properties are studied. At the same time, the mechanism of film produced is proposed. The results are as follows.First, the ceramic films on TC4 titanium alloy are fabricated under the condition of the constant cathodic and anodic voltage. During MAO process, the variations of the cathodic and anodic current against treatment time are studied, as well as the films properties such as the coating thickness, growth rate and phase component. The results show that the variations of the current curves, and the films dynamic resistance and resistivity change by stage with the increased treatment time. The coating thickness increases gradually with the increased time, while the growing rate decreases quickly at first, and then keeps constant. The films mainly consist of a large amount of autile phase and a small quantity of anatase phase. When t=15 and 60 minutes, the films contain little of TieOn. The content of rutile has a peak with the increased treatment time and cathodic /anodic voltage. The proper cathodic voltage is beneficial to the improvement of anti-point corrosion property of the coatings. When cathodic and anodic voltages are kept at 45V and 320V for 30minrespectively, the rutile content of the film is more than 80%, and showing good performance of anti-point corrosion. In the Na2COs aqueous solution, the critical voltage of electrical breakdown decreases with the enhanchment of cathodic voltage.Second, the effects of the anodic current density (/? and the radio of cathodic to anodic current density () on the properties of MAO coatings on TA2 pure titanium are investigated in detail under the condition of keeping current density constant, as well as treatment time. Our results are:(1) With the increased treatment time, the coating thickness increases, while the growth rate gradually decreases. When y'/V=0. 7 the coating thickness increases against the enhancement of . When jc/ja =0 the coating thickness increases with the enhanced ja from 15A/dm2 to 22A/dm2, and then decreases with the enhanced ja. The rule of the coating thickness changing withy is different, whenyfl is varied.(2) The films consist only of rutile phase and anatase phase. The content of rutile increases linearly with the increased treatment time from 5min to 30min, which of anatase decreases linearly with time, when tlTmin their content are equal. Increasing is advantageous for the increase of rutile content, but increasing jc/ja do so for anatase content.(3) The coated surface shows a porous microstructure. Increasing the treatment time andyfl, the size of micropore increases, but decreases with the enhanced jc/ja. And there are many grains of TiOa with size of from 60nm to 300nm on the films surface, whose size become big, and number reduce with the increased time andyl.Finally, we study the effects of the parameters of electrolytic solution on critical voltage of electrical breakdown, coating thickness. The results show that, critical voltage of MAO electrical breakdown has something to11do to with category and concentration of the electrolytic solution, as well as anodic voltage. And that decreases with the increased concentration of solution and anodic voltage. In NasPO.}, NaOH and Na2CC>3 aqueous solution respectively, the variational rule of the coating thickness against the increased treatment is different, but the growth rate all decreases with treatment time. In Na3?04 aqueous solution, the concentration of aditive-NaaB-tOy also has g... |
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