Preparation And Tribological Properties Of Carbonized Polydopamine Based Composite Films

Friction and wear are one of the main reasons for mechanical equipment energy consumption and mechanical parts failure.Solid lubricating films are widely used in aerospace and civil machinery due to their excellent friction and wear properties.Dopamine（DA）can be oxidized and self-polymerized into polydopamine（PDA）in weak alkaline environment.PDA contains abundant phenolic hydroxyl and amino groups,which can provide electrostatic force to Ag⁺and GO.PDA can be carbonized after high temperature heat treatment and converted to carbonized polydopamine（CPDA）with graphite-like structure through pyrolysis.In this paper,PDA was used as reducing agent and modifier to compound with nano-silver and graphene oxide（GO）respectively,and a series of carbonized nano-composite films were prepared after high-temperature heat treatment.X-ray diffraction（XRD）,thermogravimetric analysis（TGA）,Raman spectroscopy（Raman）,Fourier transform infrared spectroscopy（FTIR）,field emission scanning electron microscopy（FE-SEM）and X-ray photoelectron spectroscopy（XPS）were used to analyze the crystal structure and morphology of the materials.And the tribological properties of these composite films as solid lubricating films were investigated.The main research contents are as follows:（1）Based on the adhesion and weak reducibility of dopamine,PDA/Ag composite nanoparticles were prepared by in situ reduction of Ag（NH₃）₂OH.It was sprayed onto a polished copper base surface premodified by dopamine using a surface spray technique.Then,the CPDA/Ag composite films were obtained in an argon gas tube furnace at different temperatures,and the tribological properties of the composite films were studied.The experimental results showed that the friction coefficient and wear rate of CPDA/Ag composite film are the lowest at 500°C,which is 43.3%lower than that of pure copper.N-doped graphitization like friction film was formed on the substrate surface.（2）Graphene oxide and dopamine were successively added into the prepared weak alkaline buffer solution,and then mixed evenly and sprayed on the polished copper substrate surface premodified by dopamine.Then,CPDA/rGO composite films were obtained in argon tube furnace at different temperatures.The results show that the composite film coated with CPDA/rGO has good friction reduction and wear resistance after heat treatment.The wear rates of pure copper substrate and PDA/rGO composite films after heat treatment at 300°C were 3.32×10^-4 mm³/N·m and 2.08×10^-4 mm³/N m at the speed of 2 mm/s,respectively.The wear rate was 37.3%lower than that of pure copper.The main wear forms are adhesive wear and particle wear.The main elements of friction transfer film formed on the worn surface are C,N,O and Cu,which played a key role in reducing friction and increasing wear resistance.