Optimization Of Superhydrophobic Properties And Corrosion Resistance Behavior Of Titanium Alloy Surface With Micro-nano Structure

Titanium alloys are widely used in machinery,military,and medical fields due to their many excellent properties.Among them,titanium alloy materials are bound to be corroded when they are used in the marine environment for a long time.By adjusting the surface structure,the hydrophobicity of the titanium alloy surface can be improved,thereby enhancing the water-repellent and anti-corrosion ability of titanium alloy materials.The biomimetic micro-nano structure has super-hydrophobicity.The preparation of biomimetic super-hydrophobic micro-nano structure by laser etching technology is considered an effective method to improve the water-repellent and anti-corrosion performance of the material surface.After the biomimetic-nano structureture on the surface of titanium alloy reduces its high surface energy,with the increase of roughness,the hydrophobicity of titanium alloy increases,thereby improving its water repellency and anticorrosion ability.Therefore,to improve the water-repellent and anti-corrosion ability of titanium alloy materials,domestic and foreign scholars focus on preparing biomimetic micro-nano structures with a certain roughness to adjust their hydrophobic properties.Based on this,this paper optimizes the laser etching process parameters of TC4 titanium alloy to prepare precise biomimetic micro-nano structures,studies the relationship between the laser etching process parameters and the morphology of the micro-nano structures,and clarifies the relationship between roughness and contact angle.Formation mechanism of the superhydrophobic surface under different roughness,revealing the relationship between the superhydrophobic micro-nano structure of titanium alloy and self-cleaning,corrosion resistance,durability,wear-resistance,and performance enhancement mechanism.Based on the optimization experiment of femtosecond laser etching parameters,the Box-Behnken design（BBD）method is used to establish the response surface model between the etching parameters,roughness Rz and contact angle under femtosecond laser.All the models are significant,the fit is good.The response surface model analysis shows that with the decrease of the repetition frequency and the increase of scanning times,the roughness gradually increases;with the decrease of scanning distance and the increase of scanning times,the contact angle gradually increases.The roughness Rz is between 22-36μm,which is the optimize al range of hydrophobicity.When the roughness Rz is 22μm,the maximum contact angle is 158.3°.The optimal etching parameters are the laser frequency of 700 KHz,the scanning interval of 10μm,and the number of scans 16 times.The number of scans is the main factor affecting the roughness Rz and contact angle of the micro-nano structure,and the scanning distance is the main factor affecting the morphology of the micro-nano structure.After silanization treatment,with the increase of roughness,the contact angle gradually increased.The formation mechanism of the micro-nano structure was studied,and the results showed that the thermal diffusion of femtosecond laser with Gaussian distribution of laser energy was not obvious,and the micro-nano structure of titanium alloy was formed under the combined action of heat,thermal stress,compressive stress,and ultra-high laser energy.The difference in hydrophobicity of titanium alloy surfaces with different roughnesses was analyzed,and the results showed that the content of oxides such as Ti O₂ increased significantly after etching,and the elements of O and C increased.A layer of heptadecafluorosilane film is formed on the surface of the silanized sample.The greater the roughness of the sample,the more C,F,and Si elements,and the easier it is to achieve better superhydrophobicity.The silanols generated after the hydrolysis of fluorosilane react with hydroxyl groups（-OH）to remove H₂O molecules,and the silanol groups（-Si-OH）will also undergo lateral condensation or vertical condensation into hydrophobic siloxane bonds（Si-O-Si）.silanols and other active groups also react and bond,thereby reducing the high surface energy to achieve a superhydrophobic state.With the increase of roughness,the specific surface area of the titanium alloy increases,the adsorption of the fluoro silane film on the surface of the titanium alloy increases,and more bonding effects achieve lower surface energy,thereby achieving better superhydrophobicity.Based on the wetting state model,it is known that with the increase of roughness,the repulsion to droplets is stronger,and the micro-nano structures are more hydrophobic.Combined with the electrochemical polarization curve analysis of titanium alloy,it is found that the corrosion resistance of titanium alloy substrate is poor.With the increase of roughness,the electrode potential gradually moves positively,the surface corrosion current density decreases,the protective effect of the"air cushion"is enhanced,and the superhydrophobicity is enhanced.The corrosion rate of micro-nano structures is reduced.The corrosion inhibition rate of the superhydrophobic micro-nano structures with different roughness reaches 70.5%-97.3%,showing good corrosion resistance.Through the observation of the morphology and the analysis of the composition after corrosio n,it is found that with the laser-induced periodic surface structure being damaged by pitting and corrosion pits,the organic thin layer,on the surface falls off,resulting in a decrease in the content of C,F and Si elements,and the hydrophobicity gradually fails while the corrosion degree increases.Under the salt spray test conditions,the superhydrophobic samples with a roughness of 34μm degrade slowly in hydrophobicity and have good durability,showing good stability.The self-cleaning test and droplet behavior observation show that the superhydrophobic surface of titanium alloy has the excellent self-cleaning ability,strong water repellency,and low adhesion.Due to thicker air film layers,the rougher superhydrophobic samples have lower rolling angles.The cyclic friction test results show that under the condition of constant contact stress,with the increase of surface roughness,the wear resistance of titanium alloy micro-nano structure decreases,the decrease of hydrophobic angle increases,and the hydrophobicity fails faster.