目的 通过提高钛合金表面的疏水性,增强抗腐蚀能力,降低钛合金在海洋环境中由于腐蚀行为产生的氢脆风险,提高钛合金构件的使用寿命。方法 首先采用化学刻蚀法在钛合金表面制备微米级粗糙结构,随后采用阳极氧化法制备二氧化钛纳米管,并进行热处理,实现表面由亲水到疏水的润湿性转变。采用SEM、EDS、XRD、接触角测量仪、粗糙度轮廓分析仪对其表面微观形貌、成分、润湿性能和粗糙度进行表征。结果 化学刻蚀形成微米级金字塔结构,阳极氧化生成纳米级二氧化钛纳米管,二者共同构建了阶层微纳结构。此外,与原始钛合金相比,表面接触角增加到156°,开路电位值正移至0.09 V（vs. SCE）,维钝电流密度由5.38×10-5 A/cm2降低至4.39×10-8 A/cm2。同时,试样的电荷转移电阻在阳极氧化后增加到1.42×106 Ω·cm2,并且热处理后,电荷转移电阻进一步提高到2.46×107 Ω·cm2,耐腐蚀性能显著提高。结论 通过在钛合金表面进行简单的刻蚀和氧化等方法,无需低表面能物质修饰,即可获得超疏水表面,最终实现提高钛合金表面耐腐蚀性能的目的。
Abstract
The work aims to reduce the risk of hydrogen embrittlement caused by the corrosion behavior of titanium alloy in the marine environment and improve the service life of marine equipment by improving the hydrophobicity of the titanium alloy surface to enhance its corrosion resistance. In this study, a three-step method is used to construct a micro-nano hierarchical structure on the surface of titanium alloy. Firstly, by chemical etching, the polished titanium alloy substrate is etched using a mixed solution containing a strong acid. By precisely controlling the concentration and reaction time of the etching solution, a uniform micron-scale pyramid-like convex structure is successfully prepared on the surface, which provides an ideal substrate for subsequent nanostructure growth. Secondly, by anodic oxidation, electrochemical oxidation is carried out in ethylene glycol electrolyte containing ammonium fluoride with etched rough surface as anode. By optimizing the oxidation voltage and time, highly ordered and vertically oriented titanium dioxide nanotube arrays are grown in situ on the micron pyramid. This step critically forms a hierarchical micro-nano composite structure. Finally, the sample is subject to heat treatment in an air environment. This process not only removes the adsorbed water and some hydroxyl groups on the surface, but also promotes the transformation of amorphous titanium dioxide into a more stable anatase phase. The surface morphology, phase composition, wettability and roughness before and after modification are systematically characterized by scanning electron microscope, X-ray diffractometer, contact angle measuring instrument and surface profiler. The open circuit potential, potentiodynamic polarization curve and electrochemical impedance spectroscopy of the samples are tested in simulated seawater environment by electrochemical workstation to quantitatively evaluate their corrosion resistance. The formation mechanism of the micro-structured surface during chemical etching can be elucidated as follows: insoluble reaction products initially deposit on the titanium alloy surface. However, the formation and escape of hydrogen bubbles disrupt the uniformity of this deposited layer. This disruption results in preferential etching, where ravines rapidly form in the weakened or exposed areas, while the regions protected by more sediment remain elevated as protrusions. This cyclic process ultimately constructs a uniform pyramid morphology on the surface. The formation mechanism of the microstructured surface during anodic oxidation can be elucidated as follows: at the bottom of the nanopores, a dynamic equilibrium is achieved between the continuous electrochemical oxidation of titanium and the chemical dissolution of TiO2 by fluoride ions, driving the vertical growth of the tubes. Meanwhile, the tube walls are relatively "protected", resulting in a slower dissolution rate of the oxide, which allows them to remain intact. Ultimately, a highly ordered nanotube array is formed. The surface of the original titanium alloy is smooth, and the contact angle is about 70 °, which is hydrophilic. After chemical etching, a micron-scale rough pyramid structure is formed. The surface roughness is significantly increased from 0.06 μm to 1.97 μm, and the contact angle increases. Heat treatment is the key to achieve superhydrophobicity. After treatment, the surface contact angle increases to 156°, showing excellent superhydrophobic properties. In the electrochemical test, compared with the original titanium alloy, the open circuit potential of the superhydrophobic sample shifts positively to 0.09 V, indicating that its thermodynamic stability is higher. More significantly, the corrosion current density decreases by three orders of magnitude, from 5.38 × 10-5 A/cm2 to 4.39 × 10-8 A/cm2, indicating that the corrosion is greatly inhibited. Electrochemical impedance spectroscopy analysis further confirms this point: after anodic oxidation, the charge transfer resistance increases to 1.42 × 106 Ω·cm2, and after heat treatment to form a superhydrophobic surface, the resistance further soar to 2.46 × 107 Ω·cm2. This huge impedance increase is attributed to the synergistic effect of "physical barrier" and "chemical barrier". On the one hand, the stable air layer captured by the superhydrophobic surface prevents the direct contact between the electrolyte and the surface; on the other hand, the anatase TiO2 nanotube layer with higher crystallinity is itself a dense and stable protective film, which can effectively block the transmission of charge and corrosive media. In conclusion, the method of "chemical etching-anodic oxidation-heat treatment" is used to successfully prepare the surface of titanium alloy with superhydrophobic properties without modification of low surface energy materials, which achieves the purpose of improving the corrosion resistance of titanium alloy surface and provides conditions for marine corrosion protection of complex parts.
关键词
耐腐蚀 /
超疏水 /
二氧化钛纳米管 /
阳极氧化 /
热处理
Key words
corrosion resistance /
superhydrophobic /
titanium dioxide nanotubes /
anodic oxidation /
heat treatment
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基金
国家自然科学基金面上项目（51875299）
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