Study On Preparation And Properties Of Nanophase Modified Copper-iron-based Oil-impregnated Bearing Materials

Powder metallurgy copper-iron-based oil-impregnated bearing has been applied in more and more fields in recent years because of its low friction coefficient and stable operation.Since the sintering temperature of copper-iron-based oil-impregnated bearing materials are usually below the melting point of copper,less liquid phase is generated during sintering,the metallurgical bond between copper alloy powder particles and iron powder particles is poor,and the capacity of the bearing materials are relatively low.In order to improve the mechanical properties and friction and wear properties of copper-iron-based oil-impregnated bearing materials,we usually start from the aspects of sintering process,alloying elements and reinforcement.In this study,Cu Zn-Fe-P-Sn-C bearing materials had been prepared by powder metallurgy.First,the optimal compact density and sintering process of copper-iron-based oil-impregnated bearing materials are explored.Then nano-WC particles or nano-Cu were added to copper-iron-based oil-impregnated bearing materials to investigate the effects of the type and amount of nanophase on the microstructure,oil content,mechanical properties and friction and wear properties of bearing materials.Copper-iron-based oil-impregnated bearing materials were prepared under different compact density?6.45 g/cm³?6.75 g/cm³?,sintering atmosphere?100%N₂?75%H₂+25%N₂?100%H₂?and sintering temperature?825??885??.The bearing materials with a compact density of 6.60 g/cm³ can take into account both oil content and comprehensive mechanical properties.When sintered under 100%N₂ atmosphere and 100%H₂ atmosphere,there are many irregularly shaped gaps and pores in the microstructure,and the oil content,crushing strength and hardness of the material are low.When sintered under 75%H₂+25%N₂atmosphere,the metallurgical bonding between the metal powder particles is sufficient,the number and size of pores in the microstructure is small and the comprehensive performance is the best.Under the atmosphere of 75%H₂+25%N₂,as the sintering temperature increases,the metallurgical bond between the metal powder particles is increased,the oil content is decreased significantly,and the hardness and crushing strength are gradually increased.The copper-iron-based oil-impregnated bearing materials prepared under the condition of compact density of 6.60 g/cm³,sintering atmosphere of 75%H₂+25%N₂ and sintering temperature of865?have the best comprehensive performance.The crushing strength,hardness and oil content are 271.1 MPa,43.7 HB and 18.8 vol.%,respectively.The effect of ball milling time?0 h-12 h?on the microstructure and mechanical properties of 1 wt.%Nano-WC particles reinforced copper-iron-based oil-impregnated bearing materials had been investigated.Studies have shown that ball milling can disperse the nano-WC particles more uniformly in the graphite,and refine the grains of the Cu₃Zn phase to enhance the crushing strength and hardness of Nano-WC particles reinforced copper-iron-based oil-impregnated bearing materials at the same time.After 6 hours of ball milling,the grains of the Cu₃Zn phase are refined and the driving force for sintering is increased.The crushing strength and hardness of the sintered samples are reached the highest,which are 223.3 MPa and 41.8 HB,respectively.When the ball milling time is too long,the deformation resistance of the metal powder particles increases significantly due to work hardening.The porosity of the material is increased significantly,and the crushing strength and hardness are decreased significantly.Copper-iron-based oil-impregnated bearing materials with different nano-WC particle addition amount?0 wt.%-1 wt.%?are prepared under the condition of ball milling for 6 h.Studies have shown that nano-WC particles are usually distributed in the pores of Cu₃Zn phase and the gap between Cu₃Zn phase and ferrite phase,which hinders the sufficient contact between the powder particles and thus hinders the formation of sintered necks.As the addition amount of nano-WC particles increases,the pore size of the microstructure is further increased,the crushing strength and hardness of the material are gradually decreased,and the oil content is increased.When the addition amount of nano-WC particles is 1 wt.%,The crushing strength,hardness and oil content of the material are 223.3 MPa,41.8 HB and 21vol.%,respectively.The friction and wear experiments show that as the addition amount of nano-WC particles increases,the friction coefficient of the material is decreased and then is increased,the wear loss is decreased and then is increased,and finally is decreased slightly.The wear mechanism is changed from abrasive wear and adhesive wear to abrasive wear,and finally to abrasive wear and adhesive wear.When the addition amount of nano-WC particles is 0.4 wt.%,the friction coefficient and wear loss of the material are the lowest,which are0.12 and 0.38 mg/min,respectively.Copper-iron-based oil-impregnated bearing materials with different nano-Cu addition amount?0 wt.%-1 wt.%?were prepared.Studies have shown that the nano-Cu promotes the metallurgical bond between the brass powder particles and the iron powder particles during sintering.The precipitation strengthening of the nano-iron-rich phase in Cu₃Zn and the copper-zinc-rich phase in the ferrite significantly improves the comprehensive mechanical properties of the material.With the increase of nano-Cu addition amount,the crushing strength and hardness of the sintered samples are gradually increased,and the oil content is decreased and then is increased slightly.Friction and wear experiments show that with the increase of nano-Cu addition amount,the friction coefficient is decreased and then is gradually increased,the wear loss is decreased and then is gradually increased,and finally is decreased slightly.The wear mechanism is changed from the combined action of abrasive wear and adhesive wear to abrasive wear,then the wear mechanism is changed to the combined action of abrasive wear and adhesive wear.When the nano-Cu addition amount is high,there is also fatigue wear.When the addition amount of nano-Cu is 1 wt.%,the comprehensive performance of the material is the best.The crushing strength,hardness and oil content are 334.1 MPa,52.3 HB,18.3 vol.%,respectively.The friction coefficient and wear are 0.18 and 0.41 g/min,respectively.