Study On Preparation Of Micro-Nano Structured 304 Stainless Steel With Extreme Wettability By Using Femtosecond Laser

In this thesis,bionic structures were produced by using femtosecond laser micro/nano machining technique on 304 stainless steel(SS304).The relationship between micro/nano structures and laser parameters(i.e.the laser pulse energy density and scanning speed)was studied;the effects of environment(ambient and vacuum)and laser pulse width on laser induced damage thresholds(LIDTs)were investigated;and the influence of micro/nano structures on surface properties(e.g.wettability,coloration and reflectivity)was also characterized.In order to achieve superhydrophobicity on SS304,surface fluorination was employed on micro/nano structure covered samples,and the durability and wettability mechanism were also discussed.The main results and achievements of this research work are summarized as follows:(1)LIDTs of SS304 were studied in air and vacuum with different laser pulse widths and spot sizes.Results showed that the LIDTs of SS304 were mainly affected by environment and pulse width.In vacuum environment,the LIDTs of SS304 under 260 fs laser irradiation were higher than those irradiated by 35 fs laser pulses.The relationship between surface micro/nano structures and laser pulse widths was also investigated.(2)Different micro/nano structures were achieved by adjusting the energy density and scanning speed of laser pulses.Firstly,in the low pulse energy density range(<0.7 J/cm~2 but higher than LIDTs),periodic ripple structures with hydrophobic properties were formed.More nanoparticles were adhered on the surface with the decrease of scanning speed,resulting the increase of surface roughness and water contact angle.Secondly,in the high pulse energy density range(>1 J/cm~2),serious surface ablation occurred.Nano-particle and nano-particle group were observed on the ablated surface,and the surface showed hydrophilic property.With the decrease of scanning speed,the surface roughness increased and the water contact angle decreased.(3)A fluorination process was employed to improve the hydrophobicity of the sample by using 1wt%fluorosilane ethanol solution,and superhydrophobic SS304surface was achieved.Results indicated that the water contact angles of the samples with and without fluorosilane modification increased after preserving in ambient condition for six months.XPS analysis showed that it mainly relate to the formation of hydrophobic groups:A large number of hydrophobic groups formed by condensation reaction on the sample surface during the fluorination process;and after preserving in ambient condition for a duration of time,the surface of the sample reacted with air to generate hydrophobic groups.In conclusion,the micro/nano structure and wettability of femtosecond laser irradiated SS304 surface were characterized.The influence of irradiation environments on LIDTs of SS304 was systematically studied.The relationship among laser parameters,micro/nano structures and surface properties(e.g.wettability,coloration and reflectivity)was investigated.Samples with superhydrophobicity and excellent anti-reflection property were prepared.This is a fundamental research on femtosecond laser irradiated SS304,which will contribute to the development of the femtosecond laser technology and the application of SS304.