| In this paper, micro-arc oxidation process was applied to prepare an oxide ceramic coating on the surface of Ti6Al4 V alloy. All experiments were executed under constant current mode and in Na Al O2(10g/L) + Na F(5g/L) + KOH(5g/L) composite electrolyte. The effects of current density, pulse frequency, duty cycle and additives on the thickness, surface roughness, morphology, phase components and relative content of elements of MAO coatings were investigated by eddy current thickness gauge, surface roughness measuring ins trument, XRD, SEM and EDS. To evaluate the mechanical properties of MAO coatings, micro hardness and adhesion between ceramic coating and substrate were tested. The anti- fouling properties of titanium substrate and ceramic coatings were studied by shallow marine immersion experiments. The results show that:Voltage-Time curve can be divided into three stages under different electrical parameters, corresponding to the anodic oxidation stage, spark discharge stage, and micro-arc discharge stage. The thickness and surface roughness increase with the increase of current density and the decrease of pulse frequency. As duty cycle increases, the surface roughness increase and the thickness has a small variation. There are a large number of crater- like micro pores on the surface of MAO coatings. With the increase of current density and duty cycle and the decrease of pulse frequency, the number of micro pores decrease s and the diameters of the pores increase. The main composition of MAO coatings are rutile Ti O2 and Al2 Ti O5. With the increase of current density, the content of rutile increases, but the content of Al2 Ti O5 is almost constant. With the increase of duty cycle, the content of rutile and Al2 Ti O5 increase. The pulse frequency has a small influence on phase co mposition.After adding different concentration of copper ammonia solution, EDTA-Cu and K2Cr2O7 into the electrolyte, the thickness and surface roughness of the MAO coatings increase with the increase of copper ammonia solution concentration. As EDTA-Cu concentration increases, the thickness reduces while the surface roughness firstly increases and then decreases. The thickness and surface roughness have an opposite trend with the increase of K2Cr2O7 density.After adding additives, the MAO coatings are mainly composed of rutile, anatase and Al2 Ti O5. When the concentration of copper ammonia solution and K2Cr2O7 reach 2.5g/L and 1.25g/L respectively, there emerge copper compounds and chromium compounds in the coatings. With the increase of copper ammonia solution concentration, the content of rutile decreases, but the content of anatase increases obviously. With the increase of EDTA-Cu concentration, the content of rutile increases, but anatase and Al2 Ti O5 decrease. There is no copper compound in the coating when adding EDTA-Cu. With the increase of K2Cr2O7 concentration, the contents of rutile and Al2 Ti O5 decrease and the content of anatase increases.The micro hardness of specimen increases dramatically after MAO treatment. Micro hardness order from high to low is copper-containing coating, chromium-containing coating, and ordinary coating. Scratch experimental results show that the MAO coating has a high binding force with the substrate, which the binding strength is 18.1N.After MAO treatment, the specimen covered with MAO coating obtains a higher anti- fouling property than substrate. Copper-containing coating and chromium-containing coating have the sharpest improvement in anti- fouling property. Most of the fouling areas on specimens are defaced by oyster, and bryozoans followed. Ordinary coating and copper-containing coating can inhibit the growth of oyster, lime insects and barnacles, while chromium-containing coating has the best effect on anti bryozoans fouling. |
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