The Research Of Surface Wettability Of Ti?Ti6Al4V By Laser Micromachining

In recent years,people have got a lot of inspiration with the research for characteristics of biological surface in the nature.From the lotus leaf effect,it has been found that hydrophobic surface has excellently potential advantages in the aspects such as self cleaning,fluid transportation,corrosion resistance and so on,so the preparation of superhydrophobic materials has become a research hotspot in recent years.According to the theory of wettability on the material surface,the surface hydrophobicity is associated with surface energy and microstructure.In order to obtain hydrophobic surface,therefore,reducing the surface energy or fabricating the surface microstructure has become the most direct methods.By contrast,fabrication of surface microstructure is an effective approach to obtain the hydrophobic material.With laser processing method getting more and more perfect and mature,compared with other processing methods,ultrafast laser processing technology has become a popular processing technology in microstructure fabrication because of its great advantages of non-contact processing way,small mechanical deformation,high processing precision,wide range of materials.Firstly,the theory of solid surface wettability was expatiated in this paper.Then based on classical models of wettability,three special kinds of microstructures were modeled and the theoretical calculation formulas of contact angle were deduced.According to the obtained models,nanosecond laser was used to fabricate different types of microstructures on Ti and Ti6Al4 V surface,and for each microstructure,the distance between two adjacent structure units was changed in processing experiments.Through the morphology of microstructure characterization,contact angle measurement and chemical composition analysis for each microstructure,it has been confirmed that laser processing method can be applied to machine material efficiently and accurately for the desired surface microstructure.After laser treatment,the maximum value of contact angle of Ti is 157.2°,the surface is superhydrophobic,and the maximum surface contact angle of Ti6Al4 V is 137°,the surface presents hydrophobicity.The surface microstructure will not change after laser machining,so the effect of microstructure on surface wettability only exists in the moment of laser processing,and the analysis of the chemical composition indicates that the surface chemical composition changes by time,so the variation of contact angle over time is due to the change of the surface chemical composition during a period of time after laser processing.In general,the change of surface wettability from hydrophilicity to hydrophobicity by laser processing is related with surface microstructure and surface chemical composition.In order to further study the influence factors of material surface hydrophobicity,firstly,the hydrophobic materials were processed with low temperature annealing treatment with 300? for 1h,it is found that the annealing treatment can make the hydrophobic surface become hydrophilic temporarily,after a certain time it recovers the original hydrophobicity.Additionally,the influences of laser processing parameters on the surface hydrophobicity also have been studied.By changing laser power and scanning speed within a certain range,it is found that the larger laser power and the smaller scanning speed can produce better surface hydrophobicity.Therefore,in the preparation of hydrophobic surface through laser processing,the laser parameter and microstructure size should be optimized reasonably so as to obtain ideal hydrophobic surface.