Research On Preparation And Properties Of Micro-arc Oxidation Composite Ceramic Coatings Of TC4 Titanium Alloy

Comparing to a single component ceramic coatings by micro-arc oxidation(MAO), the composite MAO ceramic coatings are generally considered as the more promising application for surface modification of titanium alloys due to their better surface properties. Therefore, in the present study, the composite MAO ceramic coatings on TC4 titanium alloy were fabricated with adding Si C and Si O2 particles to evaluate the improvement of surface properties, respectively. In details, the effects of Si C and Si O2 ceramic particles addition on the microstructure, element distribution, phase composition, corrosion resistance and wear behavior of MAO ceramic coating were analyzed by SEM, XRD, electrochemical workstation and a MMA-1 model friction and wear tester respectively.Firstly, the electrolyte system of Na2 Si O4,(Na PO3)6 and Na2WO4 was chosen for MAO coatings fabrication. In order to obtain the optimum concentrate of the electrolyte for MAO coating fabrication, the orthogonal experiment was designed with the surface morphology and thickness of MAO coatings as evaluation criterion. The effect of electric parameters(positive voltage, pulse frequency, duty cycle) and oxidation time for MAO coating fabrication was studied by single factor method, and thus obtaining the optimum processing parameters. According to the experimental results shown, the optimal concentrate of the electrolyte solution are 6g/L Na2 Si O4, 5g/L(Na PO3)6, 2.5g/L, Na2WO4 and 1.5g/L KOH; the optimum technology parameters are 450 V, 300 HZ, 30% and 25 min.In addition, the influence of Si C and Si O2 additives on the phase composition, microstructure, wear and corrosion resistance of MAO ceramic coatings were also investigated with the optimum electrolyte mentioned above. The results show that both Si C and Si O2 additives introduce the obvious modification effect on the improvement of density, smooth and thickness of MAO ceramic coatings. With the addition of 9g/L Si C and 6g/L Si O2, the MAO ceramic coatings possess the highest thickness of 20.7μm and 21.8μmm, respectively, which are composed of α-Ti, rutile Ti O2, anatase Ti O2 and Si C/Si O2 by XRD analysis. Furthermore, the new β-Si C phase was detected by XRD in the MAO coatings containing Si C, which indicates that there should exist a phase transformation of α-Si Câ†'β-Si C during the MAO processing. Based on the results of wear test, it is indicated that the MAO coatings with 9 g/L Si C and 6 g/L Si O2 addition exhibit the optimal wear-resisting performance. The wear resistance of MAO coating with 9 g/L Si C and 6 g/L Si O2 increase by 180% and 133% respectively than that of MAO coating without addition. Moreover, the MAO coating with 9 g/L Si C and 6 g/L Si O2 addition also demonstrate the better corrosion resistance due to the improved electrode potential. In conclusion, both the Si C and Si O2 particles are evaluated as the effective additives to improve the wear and corrosion resistance of MAO ceramic coatings on the TC4 titanium alloy.