Study On Structure Design,preparation And Self-lubrication Mechanisms Of Surface Micropores Of M50 Matrix Self-lubricating Materials

Metal-based self-lubricating materials are widely used under the service conditions such as high-temperature,heavy-load and vacuum.However,at present,there are some problems about the tribological study of metal matrix self-lubricating materials,such as material strength defects,as well as difficulties in adjusting and controlling the lubricity due to the preparation methods and structural design.Secondly,there is a lack of enough research on the dynamic evolution behavior such as the plastic flow action of soft metal lubricants and oxidation.As a result,the material lubricating life is insufficient.Meanwhile,tribological design and its corresponding theoretical researches are seriously lacking.In this thesis,M50 steel is taken as the research object.The frictional interfacial structure with surface micropores is designed and manufactured by laser additive manufacturing technology,and the lubricant is made into the surface micropores to improve the material strength and tribological properties.Using the method of combining theory with experiment,the influence law of tribological behavior is explored.The influence mechanisms of the flow forming film of soft metal lubricants,oxidation and physicochemical reactions on the friction and wear resistance of M50 self-lubricating material are explained.The regularity understandings about dynamic evolution mechanisms of lubricating behavior and the function control factors of tribological properties are obtained.It could provide reference and guidance for tribological design and mechanical part engineering application of self-lubricating materials fabricated by laser additive manufacturing.The main achievements of this thesis are as follows:?1?According to the characteristics of soft metal lubricants,Sn,Ag and Cu are initially set as the basic components of composite lubricant.Sn-Ag-Cu composite soft metal powders with different contents are prepared by vacuum atomization technology,and their wettability and tribological properties are studied.The results show that the composite soft metal lubricant 50Sn40Ag10Cu has both excellent wettability and lubricating properties,and it is suitable for forming micropores on the surface of M50 substrate as a solid lubricant.?2?The friction interface structure of surface micropores is designed and fabricated,and the composite soft metal lubricant Sn-Ag-Cu is directly formed in the surface micropores.The effects of micropore structure parameters such as micropore depth,micropore diameter and linear porosity distribution on the surface mechanical properties of materials are investigated.The friction and wear behaviors of M50-based self-lubricating materials with surface microporous structure are analyzed by modern analytical and testing techniques.The results show that M50self-lubricating material has the best mechanical and tribological properties when the friction surface micropore depth is 400?m,the micropore diameter is 100?m,and the porosity is 20%.?3?The friction and wear behaviors of M50 self-lubricating material with surface micropores filled with Sn-Ag-Cu in the various temperature range are investigated under different friction stages,and the mechanisms of Sn-Ag-Cu precipitation,spreading flow and film formation in micropores are studied.It is found that the precipitation of lubricant Sn-Ag-Cu in the surface micropores is a dynamic process.With the development of friction,Sn-Ag-Cu continues to spread on the worn surface,resulting in the formation of lubricating film rich in lubricant Sn-Ag-Cu on the worn surface.In addition,a bearing layer for the lower part of lubricating film is formed during the friction process.The bearing layer has the phenomenon of grain refinement and high hardness,and bears most of the load,which provides a guarantee for the lasting lubrication of lubricating film.?4?In this thesis,a series of deep lubricating mechanism of lubricating film formation on friction surface has been studied.It is found that the main elements of lubricating film are Sn,Ag,Cu,O,and a series of physical chemical reactions have taken place during the friction process,and some intermetallic compounds and oxides such as Fe₂O₃,CuO,Ag₃Sn,Cu₆Sn₅,FeSn and FeSn₂ have been formed.These materials can obviously improve the strength of surface lubricating film,the damage resistance and wear resistance of material.In addition,the flow of Sn-Ag-Cu and the oxidation of Sn and Cu lead to the self-healing behavior of worn surface cracks.These behaviors are the main factors leading to the excellent lubricating properties of microporous self-lubricating materials.?5?Based on the theory of fluid lubrication and capillary dynamics equation,the precipitation dynamics model of lubricant Sn-Ag-Cu in micropores is established,and the main factors affecting the amount of lubricant precipitation are investigated.In addition,the friction surface topography parameter model is established,the coverage of lubricant on friction surface is investigated according to the precipitation volume of lubricant,and the lubrication performance optimization is carried out.It is found that the surface profile of M50 self-lubricating material,experimental temperature,micropore diameter,micropore depth,wettability between lubricant Sn-Ag-Cu and M50 matrix,lubricant's own kinematic viscosity are the main factors that control the self-lubricating function of self-lubricating material.The effects of various parameters on the tribological properties of self-lubricating materials are clear,and the theoretical research methods of friction lubrication process are expanded to enrich the tribological theory.