| Recently，hydrophobic/superhydrophobic surfaces have aroused considerable attentionsin various fields due to their excellent properties and great application potentiality. With lowsurface free energy, hydrophobic/superhydrophobic coating is considered to be an effectivemethod to improve micro-tribological properties in the field of MEMS/NEMS, and theirwater-repellent property endows substrates better corrosion resistance. The increasing tensionin energy resources makes the acceptance of light alloys wider. Fabrication ofhydrophobic/superhydrophobic surface on light alloy is of great significance on the settlementof tribological and corrosion problems.In this research, three different hydrophobic/superhydrophobic films were prepared onpure titanium, pure aluminum and ZK60magnesium alloy respectively. Moreover, theproperties of as-prepared coatings were investigated. Several important conclusions areshowed as follows:(1) An acid and alkali-resistant superhydrophobic coating with mechanical stability wasfabricated on pure titanium by thermal oxidation and self-assemble technology. An oxidationfilm with micro-nano roughness was obtained after thermal oxidation, making the substrateturn to superhydrophilic. However, after modification with self-assembled molecule, thesurface became superhydrophobic, with its static contact angle arising from29.9°to166.0°and surface free energy falling from39.58mJ/m2to5.36mJ/m2. Its rolling angle was just2°.What’s interesting was by controlling thermal oxidation condition, surface topographychanged and the surface’s superhydrophobicity switched from sticky state to roll-off state.When the surface was covered with granular oxide, water tended to stick on surface whilewhen the surface was covered with coral-like or branch-like oxide, water tended to roll off onsurface. The as-prepared coating also showed superhydrophobicity to corrosive solution withpH value varying from1to14and stay superhydrophobicity after immersion in corrosivesolution for certain time. The results of potentiodynamic polarization measurement alsorevealed that superhydrophobic coating had enhanced anti-corrosion property in3.5%NaCl solution, with the corrosion current decreased from5.66×107A/cm2to5.10×109A/cm2. Inaddition, the obtained film maintained superhydrophobicity after sandpaper abrasion andshowed mechanical stability, which could be attributed to dual-scale roughness structurecomposed of the ladder-like structure and coral-like structure.(2) Dislocation etching and polymer-plating technique were used to fabricatesuperhydrophobic surface on pure aluminum. The monomers of organic film (ATP) firstlyreacted with metal substrate and then polymerized to produce polymer films.5min was themost suitable time for galvanostatic polymer plating at0.15mA/cm2. And the as-preparedATP film has the max thickness of68.8nm and static contact angle of122.1°. In the sametime, surface free energy reached as low as8.74mJ/m2. It’s found that etching with Beckreagent for15s made the aluminum surface form maze-shape structure and after polymerplating, the surface turned into superhydrophobic with a static contact angle of161.1°androlling angle of1°. At the same time, its surface free energy reached as low as0.17mJ/m2.The micro-tribological behavior of aluminum surface after different treatment was studied. Inconstant rate of loading experiments, friction coefficient of substrate reduced from0.65to0.60after etching treatment. The friction coefficient of ATP film was0.30, while that ofsuperhydrophobic film was0.18. In constant loading of50mN experiments, the frictioncoefficient of ATP film stayed around0.30before the film was broken after50s, while that ofsuperhydrophobic film stayed around0.10before the film was broken after200s. The resultsrevealed that superhydrophobic film better improved the tribological performance ofsubstrate.(3) A color-tunable hydrophobic film with good anti-corrosion property was fabricatedon ZK60magnesium alloy. The color of surface changed with the increasement of thicknessof transparent Mg(OH)2coating formed after hydrothermal process, in the effect ofhydrothermal time. Hydrothermal process created petal-shaped structure on ZK60magnesiumalloy and made the surface become more and more hydrophilic with increasing treating time.After5h, the surface turned into superhydrophilic with static contact angle of0°and surfacefree energy of74.86mJ/m2. However, after stearic acid modification, the surface turned into hydrophobic, whose static contact angle could reach as high as118.7°and surface free energycould reach as low as7.15mJ/m2. The corrosion behavior of as-prepared film wasinvestigated in0.1mol/L NaCl solution. The results showed that corrosion resistance ofsubstrate improved after hydrothermal process and the anti-corrosion performance got betterand better with increasing hydrothermal time. The potentiodynamic polarization curvesrevealed that the corrosion current density of hydrothermal film reduced by over two orders ofmagnitude while its protection efficiency reached as high as97.1%. And after stearic acidmodification, the surface got further improvement in corrosion resistance, with the corrosioncurrent density decreasing from2.73×105A/cm2to5.32×108A/cm2, and its protectionefficiency reached as high as99.8%. |
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