| The service conditions of mechanical components in modern industrial equipment are becoming more and more complex.The lubrication problems of mechanical components in overload,high temperature and complex medium can not be solved by adding traditional lubricants.Therefore,it is urgent to develop excellent lubricating materials to replace traditional lubricants.The copper-aluminum self-lubricating coating prepared by thermal spraying technology has excellent tribological properties.In this thesis,a variety of CuAl composite coatings were prepared by plasma spraying.Ni@g and polystyrene were used as the lubricating phase of the composite coating,and nickel chromium boron silicon was used as the reinforcing phase of the composite coating.The effects of Ni@g,polystyrene resin and nickel chromium boron silicon content on the tribological properties of CuAl composite coatings were investigated,and the wear resistance mechanism of CuAl composite coatings with different addition phases was clarified.The main research work of this thesis is as follows.（1）The effects of nickel-coated graphite with different contents on the microstructure,mechanical properties and tribological properties of CuAl composite coatings were studied.The results show that the microstructure of the composite coating containing Ni@g is more dense than that of copper aluminum coating,and the hardness of the composite coating decreases with the increase of nickel coated graphite content.Friction coefficient and wear first decreased and then increased.When the content was 10%,the friction surface failed to form an effective lubrication film,and the wear was serious.when the content of Ni@g was 20%,the composite coating had good tribological properties.A large area and continuous graphite lubricating film was formed on the friction surface of the composite coating,and the lubricating film played a certain role in reducing wear.The friction coefficient decreased to 0.18,and the wear rate was 1.57 × 10-5 mm3/N·m.When the content of Ni@g was 30%,the hardness of the composite coating decreases due to the excessive content of nickel coated graphite,and obvious delamination,cracking and spalling appear at the wear scar of the coating under continuous load,which leads to higher wear rate.（2）The effects of different test conditions（load,environmental medium and temperature）on the tribological properties of CuAl composite coating containing 20%Ni@g were studied.The results show that the load has a significant effect on the tribological properties of the composite coating.With the increase of load,more graphite is extruded into the coating matrix and forms a continuous and effective lubricating film,and the friction coefficient decreases.However,the increase of radial load promotes the cracking and even peeling of the coating,which increases the wear scar area and depth of the coating,and the wear rate increases.Environmental medium has a certain influence on the tribological properties of the composite coating.The tribological properties of the composite coating in pure water and seawater decreased.The reason is that the lubricating film can be formed on the worn surface of the composite coating under dry friction conditions.However,the water medium constantly scours the friction surface during the friction process,which inhibits the formation of graphite lubricating film,promotes the expansion of surface cracks and even induces the formation of spalling pits,resulting in high friction coefficient and wear rate.In addition,this thesis also studied the effect of temperature on the tribological properties of the composite coating.The results showed that the friction coefficient（0.43）and wear rate(3.75×10-5 mm3/N·m)of the composite coating increased with the increase of temperature.This is because at a higher temperature,the graphite lubricating film formed on the wear scar is gradually oxidized and fails.With the increase of temperature,the softening hardness of the composite coating surface decreases,making the coating easier to be ploughed,leading to the local coating peeling,thereby increasing the wear rate of the composite coating.（3）The microstructure,mechanical properties and tribological properties of CuAl composite coatings with different contents of polyphenyl resin（POB）were studied.The results showed that with the increase of POB content,the microstructure of the composite coating was loose and the hardness decreased significantly.The friction coefficient and wear decrease first and then increases.When the POB content was 10%,a lubricating film was formed on the worn surface of the composite coating,showing a slightly lower friction coefficient（0.5）and wear rate(3.78 × 10-5 mm3/N·m)than that of the pure copper aluminum coating.When the contents were 20%and 30%,the lubricating phase agglomerated and accumulated inside the composite coating.Under the continuous load,the coating was easy to break and peel from the interface between the layers and the internal defects,and the peeling between the coating and the substrate was significant,thereby increasing the wear rate(90.03 X 10-5 mm3/N·m)of the coating.（4）The effects of different contents of NiCrBSi on the tribological properties of CuAl composite coating containing 20%Ni@g were studied.The results show that after adding hard phase,the microstructure of the composite coating is more dense and the hardness are improved,but the tribological properties are reduced.Only when the NiCrBSi content is 10%,the tribological properties of the composite coating are similar to those of the CuAl-Ni@g composite coating,The friction coefficient and wear rate are 0.2 and 2.76×10-5 mm3/N·m.With the increase of NiCrBSi content,the friction coefficient and wear rate of the composite coating increase.This is because after the addition of hard phase particles,as the friction and wear progress,the hard phase particles inside the coating are extruded and peeled off,becoming the abrasive particles between the friction interfaces,which produces ploughing effect on the surface of the coating,increases the number of furrows on the surface of the coating,and destroys the graphite self-lubricating film formed on the surface of the wear scar.Therefore,the friction coefficient and wear rate of the composite coating increase.In this thesis,CuAl-based self-lubricating coating was prepared by plasma spraying technology.The results show that the tribological properties of CuAl-based coating can be improved by adding appropriate amount of Ni-coated graphite lubrication phase,and the composite coating has certain self-lubricating properties.The research in this thesis laid the foundation for the preparation of CuAl self-lubricating coating and provided experimental guidance data for expanding the application of the coating in actual working conditions. |
PDF Full Text Request