Effect of the duty cycle adjusting of alternate narrow pulse on the microarc oxidation coatings on titanium alloy

Ceramic-like coatings were formed using alternate ultra-narrow pulse microarc oxidation method on alloy Ti6A14V in Na₂SiO₃-KOH-(NaPO₃)₆ aqueous solution. A constant voltage (U=500 V) regime of microarc oxidation was applied to reveal the effect of positive pulse duty cycle on their growth rate, microstructure and phase composition. In order to obtain the optimum process, a constant current density (J=60 mA/cm²) regime combined with the stepped adjusting of positive duty cycle during microarc oxidation process is also proposed. With the positive duty cycle increasing from 4 % to 20 %, the growth rate of the coatings increases and the surface morphology becomes coarser. The as-deposited coatings are mainly composed of anatase and rutile TiO₂. With the pulse duration increasing, the content of anatase decreases, while rutile increases and becomes the predominant phase. Considering the microstructure and growing thickness of the coatings, 8 % of positive duty cycle is suitable. When applying the constant current density regime, the growth rate of coatings is significantly increased compared with that by the constant voltage regime. And the morphology of the coatings is obviously improved by using the stepped adjusting of duty cycle furthermore.