Effects of cathodic voltage pulse duty cycle on characteristics of microarc oxidation coatings of titanium alloy

Under the condition of keeping the bipolar pulse voltage constant, the effect of cathodic pulse voltage duty cycle （ d c ） on characteristics of microarc oxidation coatings of titanium alloy have been studied by using a multifunction microarc oxidation power supply. Experimental results show that the variations of cathodic and anodic currents with treatment time show obviously several stages, and the beginning and ending time of various stages are closely related to d c . The coating consists mainly of rutile and anatase phases, and there is a sudden change in the rutile phase content at d c =50%. The thickness, morphology and microhardness of the coating strongly depend on d c change. The microhardness valucs of the coatings prepared at d c =50% and d c =70% are the minimum （4.96 GPa） and the highest （6.1 GPa）, respectively. In general, the MAO coatings prepared in the range of 65%≤ d c ≤80% have higher growth rate and quality.