纳秒-飞秒激光复合制备TC4合金高抗反射表面

Highly Anti-reflective Surface on TC4 Alloy Fabricated with Nanosecond and Femtosecond Lasers

单一使用皮秒或者飞秒激光器制备抗反射表面已经可以取得很好的结果,但是其加工效率不满足工业生产的需要。提出利用纳秒-飞秒激光复合制备金属高抗反射表面的方法和思路。使用纳秒、飞秒两种激光器对TC4钛合金表面进行刻蚀处理,在金属表面引入微纳米结构,使其在电磁波波长200~2500 nm间的反射率降低至2%以内并分析作用机理。首先利用纳秒激光在TC4钛合金表面刻蚀槽状结构,该结构在波长200~2500 nm的最佳平均反射率为5.76%,飞秒激光扫描后,平均反射率降低至3.5%。然后,构造复合结构在槽状结构基础上进一步优化金属表面的抗反射性能,在波长200~2500 nm的最佳平均反射率为1.87%。最后,制备复合结构,制备中其表面形貌呈现出对齐状和蜂窝状两种微孔排列方式。设计并验证控制激光脉冲起始位置方法,可制备出稳定蜂窝状结构,蜂窝状孔排列的复合结构在波长200~2500 nm的最佳平均反射率可降低至1.63%。单位面积内蜂窝状复合结构的有效表面占比更大;同时可以附着更多的纳米颗粒,由于纳米粒子的激元共振效应,加之纳米颗粒团尺寸不同,其吸收峰从单一频率拓宽至一个频率带,金属表面的光吸收性能提升。复合制备的抗反射表面性能达到甚至超越单一使用飞秒或皮秒激光器制备的金属抗反射表面,并且不改变金属本身的性质,对其他对金属表面降低反射率有借鉴作用。

The anti-reflection properties of a material surface can improve the coupling utilization of specific incident electromagnetic waves,identify electromagnetic wave signals,and shield unwanted electromagnetic waves.Such properties offer good prospects for photoelectric conduction,infrared imaging,and military stealth materials.Titanium is a transition metal with excellent biocompatibility,making it highly favorable in the medical field.Due to its high temperature resistance and corrosion resistance,it is also widely used in aerospace and military fields.According to Fresnel's law,the anti-reflective performance of the titanium alloy surface is mainly determined by the light-absorption capability of the substrate and the number of times that light is reflected by the micro-nano structures on metal surfaces.Based on the characteristics of nanosecond laser processing with high efficiency in surface texturing but processing accuracy that is inferior to a femtosecond laser for micromachining,a method for preparing a highly anti-reflective metal surface using a nanosecond laser and a femtosecond laser was developed.The geometric microstructures and surface reflectivity of the TC4 alloy surface were characterized by a scanning electron microscopy and a spectrophotometer.The nanosecond laser was used to etch the trough structure on the surface of the TC4 alloy.The thickness of the inner wall of the trough structure was changed by controlling the filling spacing of the laser scanning.The reflectivity of the structure was measured as 5.76% for a wavelength range of 200-2500 nm;the averaged reflectivity was reduced to 3.5% after femtosecond laser scanning.The anti-reflection performance of the metal surface was further optimized on the fabricated trough structures.The spacing of the micropores on the surface of the hybrid structures was changed by controlling the scanning speed of the laser beam.The number of micropores per unit area was proportional to the light-absorptivity of the surface.An optimal averaged reflectivity of 1.87% was obtained for a wavelength range of 200-2500 nm.Finally,a laser scanning route was designed and verified to prepare a stable honeycomb-like structure.The optimal average reflectivity of the hybrid structure with honeycomb-like holes could be reduced to 1.63% for wavelengths of 200-2500 nm.According to the excitation resonance effect of the particles and the different sizes of the nanoparticle clusters,the absorption peak was widened from a single frequency to a frequency band.Thus,the light-absorption capability of the metal surface was improved.In addition to surface topography,it has also been found that the surface element components of titanium alloy influence light-absorption performance.At room temperature,titanium alloy is chemically stable.However,the temperature of the sample surface increases with laser irradiation,enhancing the activation performance of titanium.As a result,oxidation occurs on the surface of titanium alloy to form TiO2;a dense oxide film is generated,which further improves the anti-reflection performance of the substrate.This study combines the high efficiency of nanosecond laser processing and the high accuracy of femtosecond laser processing to effectively improve the anti-reflection capability of metal surfaces.Furthermore,by independently designing the laser processing path,a honeycomb-like hybrid structure can be stably prepared.The reflectivity of the titanium alloy surface is further reduced,to a minimum of 1.63% for a wide range of wavelengths(200-2500 nm).Using both nanosecond and femtosecond lasers can produce a highly anti-reflective titanium substrate that reaches or surpasses the performance with single femtosecond or nanosecond laser processing.This research may also provide suggestions for similar metals.