Effect Of Solid Lubricants On Microstructure And Properties Of Metal-based Self-lubricating Materials

With the development of industry,mankind is exploring Polar Regions,oceans,and even outer space,and put forward higher requirements for the performance of mechanical parts.Many parts are used in high-speed,heavy load,poor oil,extreme temperature and even vacuum environments,which require materials not only with excellent mechanical properties,but also with good self-lubricating properties.Metal matrix self-lubricating composites have become an important research direction.At present,the main direction of metal matrix self-lubricating composite is to add solid lubricants.However,the addition of solid lubricants is generally detrimental to the bonding of the matrix and damages the mechanical properties of the material.In this paper,the effect of solid lubricant addition on the matrix and the lubrication mechanism are studied in order to prepare metal composite materials with good mechanical properties and self-lubricating properties.In this work,the effects of sintering temperature,the addition of graphite,phosphorus,and MoS₂ on the microstructure,mechanical properties,and lubrication properties of Fe-based self-lubricating materials were studied.The reaction mechanisms and lubrication mechanisms of solid lubricant and matrix were analyzed.The results show:（1）When the amount of graphite is 1～2 wt%,the sintering temperature is more suitable at1070℃.At this time,the content of compound carbon in the material is less than 0.8 wt%,and the remaining carbon elements still exist in the form of graphite,which can improve the lubrication performance of the material.Adding a small amount of phosphorus can promote the diffusion of iron atoms,spheroidize the pores during sintering,and significantly improve the mechanical properties of the material.As the amount of MoS₂ addition increases,the sulfide content in the material increases,and the self-lubricating performance is better.（2）The free graphite in the material is dispersedly distributed in the liquid lubricating oil to form a graphite-lubricating oil colloid,which can increase the stability of the oil film and reduce the friction coefficient of the material under oil lubrication conditions.Sulfide has good lubricating properties,especially it can improve the anti-friction performance of materials under high-speed and heavy-load conditions.（3）The Fe-5（Cu-10Sn）-1.5Graphite-0.3P-1.5MoS₂ material sintered at 1070℃has the best comprehensive performance,the hardness is 68.0 HRB and the radial crushing strength is685 MPa.The average coefficient of friction under oil lubrication conditions with a linear velocity of 0.75 m·s^-1 is 0.0498.For copper-based self-lubricating materials,the effects of Ni-coated MoS₂ on the microstructure,mechanical properties,and lubricating properties were studied.The reaction mechanism and lubrication mechanism of Ni-coated MoS₂ and the substrate were analyzed.The results show that:（1）Adding Ni-coated MoS₂ to copper-based materials can increase the hardness and significantly improve the lubricity of the material.This is due to the solid solution strengthening effect of Ni on the copper matrix and the good lubricating effect of MoS₂ as a solid lubricant.（2）The nickel coated around the MoS₂ particles prevents the contact between MoS₂ and copper matrix and hinders the reaction between them.Therefore,the metallurgical bonding of the substrate is good,and the problem of poor bonding between MoS₂ and copper substrate is solved.（3）In oil-containing self-lubrication,MoS₂ in the material acts as a solid lubricant together with the liquid lubricating oil stored in the pores to play a role in lubricating.During dry friction,the MoS₂ distributed in the material matrix acts as a solid lubricant to reduce friction.（4）When the content of Ni-coated MoS₂ is 12 wt%,（Cu-10Sn）-12（Ni-coated MoS₂）composite shows the best comprehensive performance:the hardness is 66.9 HBW（2.5/62.5）;the average friction coefficient is 0.0051 under oil lubrication conditions with a pressure of 8MPa and a linear velocity of 0.75 m·s^-1,which is 83%lower than Cu-10Sn without Ni-coated MoS₂ addition;the friction coefficient is 0.1769 under a dry friction condition of a load of 4MPa and a linear friction speed of 0.25 m·s^-1,which is 51%lower than the Cu-10Sn material.