| Liquid phase plasma technology is a new type of surface modification technology,which can infiltrate trace elements such as N and C on the surface of steel to improve its hardness and wear resistance.In recent years,researchers have paid much attention to it.However,the infiltration mechanism,film formation process,electrolyte solution preparation,process parameter selection and tribological properties of the modified layer are not sufficiently deep and the research results lack uniformity and comparability.Therefore,in order to obtain excellent tribological properties,the cathode liquid phase plasma technology was used to modify the surface of 45 steel in this paper.Firstly,combined with the characteristics of the matrix material,the mechanism of cathode electrolysis and the electrochemical reaction that occur in the electrolyte were analyzed.The electrolyte solution with urea as the main ingredient was screened and prepared,and the modification experiment under different process parameters wasconducted.The morphology,microstructure,composition and microhardness of the modified layer were tested by scanning electron microscopy,energy dispersive spectroscopy,X-ray diffractometer and microhardness tester.The mass fraction of urea electrolyte,voltage and conductivity salt were analyzed.The results show that the effect of urea mass fraction and voltage parameters on the composition and microhardness of the modified layer is most obvious.As the urea electrolyte mass fraction increases,the composition of the modified layer also changes accordingly.When the urea mass fraction is low,there is only iron oxide in the modified layer.As the urea mass fraction reaches 60%,Fe2N appears in the modified layer.The thickness of the modified layer also increases significantly with increasing urea mass fraction.The change of the voltage parameters has a great influence on the microhardness of the modified layer.It is found that the microhardness of the modified layer prepared with a higher voltage is significantly increased.When the voltage is 280V,the microhardness of the modified layer is up to 1112.5 HV,which is nearly 4.0 times higher than that of the substrate.In order to further study the effect of different electrolyte compositions on the properties of the modified layer,ammonia water was first added to the urea electrolyte,and then modified experiments were carried out using formamide and glycerol alone as electrolytes.The research shows that with the increase of ammonia mass fraction,the nitrogen content in the modified layer is increased.The thickness of the modified layer is gradually increased from 57.76μm of 1.0%ammonia water to 94.08μm of 10.0%ammonia water.The microhardness is increased to 804.1 HV.The surface of the sample treated with formamide and glycerol showed that the relative nitrogen content and carbon content of the modified layer prepared by the formamide electrolyte were 12.00%and 9.69%,respectively,and the relative content of the modified layer prepared by glycerol electrolyte.The carbon content is 10.56%,while the relative nitrogen and carbon contents of the matrix are only 4.55%and 3.68%,respectively.Finally,the tribological properties of the modified layer were tested on a ball-disc tribology testing machine.The effects of urea mass fraction,voltage parameters,conductive salt species,conductive salt mass fraction,treatment time and ammonia water addition on the dry friction properties of the modified layer were studied.The tribological properties of some modified layers with good dry friction performance were tested under water lubrication and oil lubrication.The results show that the dry friction coefficient of the modified layer and the friction coefficient under water lubrication are lower than that of the matrix,and the dry friction coefficient is more obvious.Due to the presence of nitrides and carbides in the infiltrated layer,the wear resistance of the modified layer is also improved to varying degrees. |
