| In this paper,preparated nano-diamond coating on the background of field emission cathode material,and adopted the solution/suspension plasma spraying method to prepare nanostructured diamond coating.In addition,this paper optimized the preparation of the coating process,analysed the residual stress between the diamond coating and substrate,observed the microstructure and properties of the nano-diamond/HA composite coating and investigated the nano-diamond/titanium composite coating.The main results of this study are as follows:In the process of preparation of the coating,made dry sandblasting method for pretreating the surface of titanium to enhance the bonding strength of the coating and the substrate.CTAB was chosen as the dispersant of nano-diamond liquid material.Last the ultrasonic vibration method was applied to keep the nano-diamond fluid uniform and stable.Simulation resulted of plasma jet temperature field showed that the temperature field distribution of plasma jet had obvious changes with the increase of hydrogen content.The heat loss of the plasma jet was small,which the molar ratio of hydrogen and argon was 1: 4.Under this condition,when gas flow rate was 200m/s,the temperature of the plasma jet was higher.Based on the numerical simulation,the residual stress between the nano-diamond coating and the titanium substrate showed that the principal stress of nano-diamond coating was tensile stress.the maximum principal stress of the coating was mainly determined by the maximum principal stress of the coating surface when the coating was thin and the maximum principal stress increased first and then decreases.In contrast,the maximum principal stress of the coating was mainly determined by the maximum principal stress of the coating interface when the coating was thick and the maximum principal stress of the coating interface increased with the increase of the coating thickness.The maximum shear stress of the coating was transferred from the coating surface to the coating interface with the increase of coating thickness,moreover,the maximum shear stress first decreased and then remained stable.Whether the coating was a whole,its interface or its surface,the maximum principal stress and the maximum shear stress of the coating decreased linearly with the increase of coating temperature.The maximum principal stress was concentrated on the interface between the coating and the substrate and it was at the edge of the interface,but the maximum shear stress distributed in the surface of the coating.Nano-diamond particles were deposited on the surface of titanium matrix,which the main form were flat particles overlap and closed to each other.The surface of flat particles that it's topography had three different types included rough,smooth and broken.The different flattening degree of the flat particles made very uneven on the surface of the coating,resulting in dense interstices between the flat particles.But nano-diamond coating maintained a good nanoparticle size and the thickness of the coating was a few microns.By XRD,Raman spectroscopy and selected electron diffraction analysis,the main component of the coating was diamond structure,which perfectly preserved the nano-size,grain size and crystal structure of diamond.The nano-diamond/HA composite coating exhibited nanostructural features,and the nano-diamond particles filled the pores of the coating to improve the performance of the coating.The microhardness and the bonding strength of the composite coating were increased with the increase of the nano-diamond content.The nano-diamond/titanium composite coating was a layered structure,and the surface of the titanium coating was completely covered by the nano-diamond coating.In addition,the coating was formed by stacking a large number of agglomerates and had relatively small pores.The coating still exhibited nanostructure features.The coating surface was more dense and its corrosion resistance had been greatly improved. |
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