Abstract:Micro-arc oxidation processes of the dense Ti samples and the gradient porous Ti samples in H2SO4 electrolyte were studied. The effects of pore characteristics, current density, constituents of the electrolyte on initial voltage, breakdown voltage, ignition time, the morphology and thickness of oxidation coatings were analyzed. Phase composition of micro-arc coatings was measured. The results show that the gradient porous Ti samples have higher initial voltage and breakdown voltage, longer ignition time and higher coating thickness compared with the dense Ti samples during micro-arc oxidation. With the increase of current density, micro-arc oxidation reaction becomes acute. In the oxidation coatings, the pore sizes increase and the porosity decreases. Simultaneously, the roughness and thickness of oxidation coatings both improve. When La(NO3)3·6H2O is added in H2SO4 electrolyte, the initial voltage, breakdown voltage and ignition time of the gradient porous Ti samples increase. The mean pore sizes in oxidation coatings and coatings thickness increase form 200 nm to 2 μm and from 27.6 μm to 35.6 μm, respectively. The roughness of oxidation coatings also improves. XRD analysis shows that micro-arc oxidation coatings is composed of Ti, anatase TiO2 and rutile TiO2. The main existing form of TiO2 is anatase TiO2.