Influence Mechanism Of Synergistic Effect Of Nitrogen And Silicon On Corrosion Behavior Of Diamond-like Carbon Film On Aluminum Alloy Surface

Aluminum alloy is widely used in ocean,aviation and other fields because of its light weight and excellent corrosion resistance.However,when aluminum alloy is used in the marine environment,the high concentration of chloride ions in seawater can easily lead to serious pitting and delamination corrosion on the surface of aluminum alloy,which greatly limits the application and development of aluminum alloy in the marine environment.Therefore,studying the corrosion damage mechanism of aluminum alloy in harsh marine environment and providing corresponding protective measures are the key to promote the development of China’s marine industry in the direction of high efficiency,safety,environmental protection and energy saving.Surface modification is an effective method to improve the corrosion resistance of aluminum alloy materials.Plasma enhanced chemical vapor deposition technology can deposit diamond-like carbon films with excellent properties on the surface of aluminum alloy.Therefore,in this thesis,diamond-like carbon films were prepared on the surface of 2024 aluminum alloy by plasma enhanced chemical vapor deposition.The morphology of the films was characterized by atomic force microscope and scanning electron microscope.The structure of the film was tested and analyzed by infrared spectroscopy and Raman spectroscopy.The mechanical properties of the film were tested and analyzed by scratch tester and nanoindentation tester.The corrosion resistance of the film was characterized by electrochemical workstation.The seawater erosion corrosion resistance of nitrogen-doped and silicon-nitrogen co-doped diamond-like carbon films was tested by erosion device,and the microbial corrosion resistance of silicon-doped diamond-like carbon films was tested.The effects of nitrogen and silicon on the structure and properties of diamond-like carbon films were discussed.The main progress of this thesis is as follows:N doping can significantly reduce the number of defects in DLC films,thereby improving the mechanical properties and corrosion resistance.When doped with 20sccm（m L/min）N,the number of defects in the N-DLC film is less,and the hardness and elastic modulus are higher,which are 13.32 GPa and 109 GPa,respectively.In addition,the corrosion current density of DLC film doped with 20 sccm N in 3.5wt.%Na Cl solution is 1.93×10^-7A/cm²,which is two orders of magnitude lower than that of DLC film without N doping,and the corrosion resistance is significantly improved.After 15 days of seawater erosion,the content of C^sp2=N hybrid bond decreased significantly.The dissolution of N ions in the N-DLC film with N content of 20 sccm could combine with H⁺in the pore micro-region solution to form NH₄⁺,which reduced the acidification of the solution,thereby reducing the erosion-corrosion sensitivity of the film and slowing down the corrosion process.The content of C^sp2=N bond and Si-C bond in the DLC films co-doped with N and Si increased significantly,the internal stress in the films decreased significantly,and the mechanical properties of the films were improved significantly.When the flow ratio of N₂ and TMS（tetramethylsilane）is controlled at 30/30,the content of C^sp2=N bond and Si-C bond in the film is higher,and the distortion degree of the carbon-based three-dimensional network structure is weakened,thereby reducing the internal stress of the film.At this time,the hardness and elastic modulus of the film are the highest,which are 11.58 GPa and 108.4 GPa,respectively.In the N/Si-DLC film,the dissolution of N ions can combine with H⁺in the pore micro-region solution to form NH₄⁺,which reduces the acidification of the solution.In addition,the formation of Si_xO_y oxide has a certain blocking effect on the penetration of Cl^-into the interface between the film and the substrate,and the synergistic effect of the two can significantly reduce the corrosion rate of the film.In this study,the erosion durability of N/Si-DLC film is excellent when the flow ratio of N₂ and TMS is 30/30.With the increase of Si content,Si and C are easy to combine to form Si-C bond of sp³ hybrid structure,and the film tends to diamond structure,so the hardness and elastic modulus of the film are improved.A certain amount of Si doping can significantly increase the sp³ hybrid bond content in the DLC film,thereby improving the mechanical properties of the film.When the Si content is 10 sccm,the hardness and elastic modulus of the films are the highest,12.73 GPa and 98.7 GPa,respectively.The formation of biofilm has a certain degree of protective effect on the Si-DLC film during 15 days of erosion in chlorella solution.The Si-DLC film with Si content of 10sccm shows excellent microbial corrosion resistance.After erosion,the degree of film shedding is small and the degree of corrosion is low.