| Micro-cracks exists in micro-arc oxidation surface prepared on TC4 titanium alloy due to the thermal stress, this caused film and substrate bonding strength poor and poor wear resistance. And then micro-arc oxidation is a high voltage and large current process, the phase’s crystal transition in the film is not complete, resulting in a low crystal content in the film, the biologically active layer is poor. In order to solve the two shortcomings of micro-arc oxidation film, in this paper, a bio-ceramic has excellent abrasion resistance was fabricated on TC4 alloy surface using two-step methods. First, in order to improve the wear resistance of the oxide film was produced in calcium acetate-phosphate electrolyte with addition of graphite nano-particle. Second, the thermal oxidation as post-treatment to improve the crystal degree to improve the biological properties of TC4 alloy. The phases composition, surface morphology and elemental distribution were characterized by XRD (X-ray diffraction), SEM (scanning electron microscope) and EDS (X-ray spectrum analyzer),separately. The wear resistance, corrosion resistance and hardness of films were respectiveiy detected by friction and wear tester, CS electro-chemical workstation, micro-hardness tester; the SBF immersion test was assessed the biological activity of the films. The results are as follows:(1)When the current density is 15A/dm2, the frequency is 600Hz, the oxidation time is 10min, the Ca and P ratio is 2, we can prepare the porous film has same size of the micro-pores and uniform distribution on the TC4 alloy. The Ca/P of the film is reached 1.43, it is nearest to 1.67 of human bone hydroxyapatite.(2)Graphite composite oxide films consist of rutile, anatase, titanium and hydroxyapatite phases. With the content of the graphite increases, the thickness, micro-hardness, corrosion resistance and wear resistance of films were gradually improved.(3)Thermal oxidation treatment would change the surface structure of the composite films. Compared with the without thermal oxidation, when the thermal oxidation temperature less than 600 ℃, the micro-structure and morphology of the film didn’t change.While the thermal oxidation temperature exceeded 600 ℃, the number of bulk melt increases and micro-pores reduction, and there are some larger size micro-cracks on film surface.(4)Thermal oxidation treatment would change the performance of the composite films. Micro-arc oxidation film by thermal oxidation treatment could improve the corrosion resistance of the film. When thermal oxidation temperature was 200 ℃, it had best corrosion resistance among others.The thermal oxidation process was’t benefit to improve corrosion resistance and abrasion resistance of graphite composite oxide film.(5)Thermal oxidation process helped the film to induce the calcium salts. Compare with the films before immersion,when the film subjected to thermal oxidation after SBF immersion,,the calcium and phosphorus elements content increased, their calcium and phosphorus ratio increased from about 1.43 to about 2.10.(6)When the thermal oxidation temperature is 400 ℃, the graphite addition amount is lOg/1, we can prepared composite film has pore size and porous structure uniform and wear resistance and biological activity relatively well.
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