TC4钛合金超疏水表面/超润滑表面的制备及防冷凝性防冰性能研究

The Anti-condensation,Anti-icing Performance of Superhydrophobic and SLIPS TC4 Titanium Alloy Surfaces

目的为研究疏水表面与润滑表面的防冷凝及防冰机理,拓宽TC4钛合金在航空航天、医疗、化工石油、船舶制造等多个领域的应用。方法采用阳极氧化法,在TC4表面构建了不同粗糙微结构,利用扫描电镜和原子力显微镜分别对表面形貌和粗糙度进行表征,对表面进行氟化和注油后,应用接触角测量仪测试表面的接触角、滚动角和滑动角,并在恒温恒湿箱内对氟化超疏水TC4表面和注油超润滑TC4表面的冷凝行为和结冰行为进行观测。结果以HF溶液为电解液,10 V恒定电压下,在TC4表面制备得到了突触状微结构,20 V恒定电压下制备得到了排列有序的纳米管状结构。氟化改性后,纳米管状结构TC4表面接触角可达156.1°,滚动角为8°,表现为超疏水性。注油后的纳米管状超润滑TC4表面接触角为109.1°,滑动角为2°,表现为超润滑性。在冷凝测试中,超疏水表面出现了液滴自发滑移和自发跳跃行为。在结冰测试中,注油后的纳米管状超润滑TC4表面比其他测试样品表面具有最长的结冰延迟时间45 s和最低冰黏附强度8.8 kPa。结论超疏水TC4表面比其他测试样品表面具有更加优异的防冷凝性,进行注油润滑后,超润滑表面的防结冰性优于超疏水表面。

To improve the anti-condensation and anti-icing properties of TC4 titanium alloy and to broaden its practical application in aero-space,ships,medical devices,petroleum platforms etc.,microstructures with different surface roughness were fabricated on the surface of TC4 by anodic oxidation.Synaptic hair-like microstructures and regular array of nanotubular structures were prepared on the surface of TC4 samples at a constant voltage of 10 V and 20 V with HF solution as the electrolyte,respectively.After fluoridation and liquid infusion of the anodized TC4 surfaces,superhydrophobic surfaces and SLIPS were obtained.The anti-condensation and anti-icing behaviors of the superhydrophobic surfaces and SLIPS were compared and analyzed,mechanism behind were also discussed.The surface morphology and roughness of the two coatings were characterized using scanning electron microscopy and atomic force microscopy,respectively.After anodic oxidation at different voltage,regular arrays of triangular synaptic hair-like structure and titanium nanotube structures were obtained,respectively.After fluoridation,the hair-like structure surface displayed contact angles larger of 144°and rolling angle of 60°,while the nanotube structure surface presented superhydrophobicity with contact angle larger than 150°and roll-off angle less than 10°.To obtain SLIPS,the above fluorinated surfaces were infused with silicon oil under low pressure.The obtained surfaces present decreased water contact angles with sliding angles less than 10°.To investigate the condensation behaviors of the superhydrophobic surface and SLIPS,the samples were placed in a climate chamber.The temperature of the coating surfaces was set as 4℃.The environmental temperature of 25℃and relative humidity of 60%were selected.The condensation performance of the different coatings was compared at subcooled temperature of 12.7℃.During the cooling process,molecules of water vapor nucleate and grow to form tiny liquid droplets on the sample surfaces.After 30 min of cooling,these droplets grow to a certain size with an irregular shape on the polished TC4 surface.Condensates maintained their spherical shape on superhydrophobic surfaces during cooling process and presented significantly suppressed growth compared than those formed SLIPS.At the same time,jumping and sweeping of condensed droplets on superhydrophobic surfaces helped refresh of the surface area and increase nucleation barrier.The superhydrophobic surface displayed superior anti-condensation performance to SLIPS.The anti-icing performance were carried out in the climate chamber with temperature of‒20℃.The icing delay time and ice adhesion strength were characterized.Compared to superhydrophobic surfaces,the droplet on SILIPS demonstrated icing delay time of 15 s.The reason lies in two aspects,firstly,the decreased water contact angle of superhydrophobic surfaces at low temperature;secondly,the infused silicon oil in SLIPS serves as the heat insulation layers between water droplets and micro-nanostructured surfaces.The ice adhesion strength of the superhydrophobic surface and SLIPS were 13.2 kPa and 8.8 kPa,respectively.The relative high ice adhesion strength of superhydrophobic surface is due to failure of the air-trapping sites under low temperature.To sum up,superhydrophobic surfaces effectively suppress the nucleation and growth of condensates,and SLIPS displayed the longest icing delay time and the lowest ice adhesion strength are more promising in anti-icing applications.