Abstract: Effects of pulse frequency and duty ratio on microstructure and properties of microarc oxidation coatings prepared on Ti6Al4V alloy in Na₂SiO₃-Na(PO₄)₆ electrolyte system were studied. The morphology, element distribution, phase composition, thickness, roughness and microhardness of the coatings were characterized by means of scanning electron microscope, energy dispersive spectrometer, X-ray diffractometer, coating thickness meter, laser confocal microscope and microhardness tester. The results show that the main elements of Ti6Al4V alloy microarc oxidation coatings are Ti, O and Si. The phase composition is mainly Rutile-TiO₂, Anatase-TiO₂ and amorphous SiO₂. With the increase of pulse frequency, the intensity of Anatase diffraction peak in the coating decreases first and then increases, whereas Rutile shows the opposite trend. With the increase of pulse duty ratio, the intensity of Anatase diffraction peak decreases, while that of Rutile diffraction peak increases. Micro-holes are uniformly distributed on the surface of the coatings. Pulse frequency has little effect on the microstructure and roughness, and the thickness increases first and then decreases. With the increase of duty ratio, the thickness increase rapidly, but the surface gradually appears microcracks and local ablation defects, causing the roughness increase rapidly. The thickness reaches 45.46 μm and the roughness R_a is 4.75 μm at 600 Hz and 20% duty ratio. With the increase of pulse frequency and duty ratio, the microhardness of coatings increases first and then decreases. The maximum microhardness is 863.2 HV0.5 at 600 Hz and 20% duty ratio, compared with Ti6Al4V alloy, the increase is 149.5%.

Key words: Ti6Al4V alloy, microarc oxidation, pulse frequency, duty ratio