Study On The Tribological Properties Of Copper-Bismuth-Graphite Sliding Bearing Materials

Lead is widely used as an important anti-friction, wear resistance, anti-adhesion element in copper-matrix bearing materials. However, it is a harmful element. As human gradually increase the awareness of their own health and environmental awareness, lead-free products have become an inevitable trend. The selection of non-toxic low melting point element bismuth and graphite as a composite lubricating in this paper, and it is expected that the lead can be replaced by the synergy of the anti-friction and wear resistance of graphite and anti-adhesion of bismuth to obtain lead-free copper bearing materials.The copper-bismuth with graphite sliding bearing materials were prepared by the conventional powder metallurgy method and the tribological properties were conducted under different conditions. In order to investigate the friction and wear mechanism of copper bismuth with graphite sliding bearing, microstructure, worn surface morphology and surface profile, chemical composition of the worn surface were analyzed with scanning electron microscopy, EDS spectrometer, optical microscopy and other means of microscopic analysis.The results of friction and wear experiment show that,under dry friction conditions, although added the bismuth have a certain improvement the anti-friction and anti-adhesion properties of copper-based bearing materials, but brittle spalling of the wear particles resulting in significantly increased the amount of wear and poor wear resistance, it is show that the bismuth copper bearing material should not be used in dry friction conditions. Under oil lubrication conditions, the lubricant film of lead-free copper bismuth bearing material is little damage, Bi and lubricants have a synergistic effect so that reflect the good anti-friction and anti-adhesion properties. Both dry friction and oil lubrication conditions, suitable content of graphite is added, can significantly improve the friction-reducing and wear resistance of copper bismuth with graphite bearing materials. When the content of the graphite is2.0wt%, graphite and bismuth have been reflected better synergy, copper-plated graphite with bismuth reflects the better synergy effects in the anti-friction, wear-resistant and anti-adhesion characteristics.The low melting point element bismuth in Copper-bismuth sliding bearing materials melting and precipitating to direct contact region of friction surface because of frictional heat, it can help reducing shear strength of the contact area, stabling friction pairs. The graphite of the copper bismuth with graphite bearing material, under the action of friction, the graphite overbur expand in the friction pair direct contact surface, forming a stable graphite lubricating film and it can slow down the brittle Bi component fall off in the process of friction, low melting point Bi component also to improve adhesion and integrity of the graphite lubricant film, making copper bismuth graphite bearing material manifestation of good anti-friction and anti-adhesion properties. Good wettability of the copper-plated graphite and copper alloy matrix, the matrix interfacial bonding closely, stable graphite lubricating film can be formed, the better synergistic effect of the bismuth and copper-plated graphite, to further improve the antifriction and wear resistance performance of copper bismuth with graphite bearing material.