| Superhydrophobic surface is widely used in self-cleaning,anti-corrosion,drag reduction,decontamination and other fields because of its unique performance.In order to expand the application field of 316L stainless steel substrate formed by selective laser melting(SLM)technology and improve its service life,this paper presents a method of preparing structure-function double layer nickel coating on the surface of SLM substrate by scanning electrodeposition technology.The structure layer of the coating is used to repair and protect the surface of SLM substrate,and provide the original base for the forming of the function layer.The functional layer with superhydrophobicity is used to further protect the SLM substrate and structural layer.The main research contents are as follows:(1)A double groove scanning electrodeposition machine tool is designed and built,which is composed of the main transmission system,solution circulation system,nozzle and fixture system and control system.The machine tool can take the nozzle to do reciprocating scanning motion and up and down motion.(2)The basic principles and influencing factors of conventional electrodeposition,spray electrodeposition and scanning electrodeposition were analyzed.In addition,the preparation process parameters and post-treatment process of SLM substrate were also introduced.Finally,it is determined that the laser power of SLM matrix is 220 W,the laser scanning rate is840 mm/s,the thickness of powder layer is 30μm,and the scanning interval is 50μm and the substrate shall be sanded before use.(3)The effects of the current density of the structure layer,the current density of the functional layer and the scanning speed of the functional layer on the surface morphology and wettability of the coating were studied.The results show that when the current density of the structure layer is 80A/dm~2,the current density of the functional layer is 30 A/dm~2 and the scanning speed is 6mm/s,the cauliflower clusters with micro-nano structure are densely distributed on the surface of the coating and the wettability is the best,and the contact angle is about 153°.Based on the above,the forming mechanism of the coating and the formation mechanism of the wettability of the coating are also analyzed.(4)A set of processing technology and parameters for stable preparation of superhydrophobic coating were studied.According to the results of test and analysis,cauliflower clusters are densely distributed on the surface of the coating;the average grain size of the coating is 16.5 nm,which is larger than the average grain size of bright nickel coating.In addition,the mechanism of coating changing from wettability was analyzed.Through the analysis of EDS and XPS res ults,it is found that the change of wettability of the coating is caused by the spontaneous adsorption of organic matter from the air by clusters,which reduces the free energy of the coating surface.(5)The wettability,adhesion strength,corrosion resistance and stability of superhydrophobic coating were tested and analyzed.The static contact angle of the superhydrophobic coating is 153.8°and the rolling angle is only 7.6°.The adhesion strength of superhydrophobic coating is high,and the adhesion force is 24.7±3.9 N.Compared with the bare substrate,the corrosion resistance of the samples with superhydrophobic coating in 3.5wt.%Na Cl solution is greatly improved.At the same time,the superhydrophobic coating has good stability in acid salt solution and medium high temperature environment. |
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