| With the rapid development of modern industry, higher standards are proposed to require the performance of the sliding bearing materials. Copper-based bearing alloy is widely used in high speed, heavy load engines because of its high carrying capacity and fatigue strength. However, its imperative to develop lead-free copper-based bearing alloy since conventional copper-based bearing alloy contains toxic elements such as lead, which will do harm to people and the environment. The study found that non-toxic and low melting point metal element bismuth is feasible to substitute lead in copper alloy, which has similar properties to lead, immiscible with copper and may exist in copper alloy in a free form playing good lubrication. However, there is a coarse bismuth problem in the copper-based bismuth bearing alloy, and the preparation of nano-composite material by mechanical alloy(MA) method has been applied successfully, meanwhile the method of preparing Cu-Sn-Bi bearing alloy by MA method is rarely reported. In this dissertation, we attamp to prepare Cu-Sn-Bi alloy powders by MA method, and the effects of ball milling, compacting and sintering process on microstructure and properties of the alloy have been researched. At the same time, we also prepare bearing strip by rolling MA alloy powder with steel back, which microstructure and properties has been studied comparing with the industrial bearing strip.Firstly, the effect of ball milling on the microstructure and properties of MACu-10%Sn-x%Bi alloy powder was studied. Research showed that the solubility of mutually insoluble Cu-Bi system can be extended by high energy ball milling; in the milling process, the formation and decomposition of Cu6Sn5 phase can be accelerated when the milling speed increases; the MA alloy powder prepared by 450 rpm for 40 h only consists a supersaturated solid solution of Cu, which has a relatively good refining effect, the average particle size is 20 um or less, wherein the average grain size of Cu is approximately 20 nm.Secondly, the preparation and sintering process was studied, and the organizational structure and properties of the alloy was analyzed. Research found that the preparation of the bulk alloy with the use of heating and cooling in the furnace by “repressing and resintering†process, cannot be sintered at 800 ℃ if Bi content remains intact. In addition, Cu-10%Sn-5%Bi alloy sintered at 700℃ has relatively better mechanical and tribological properties except its lower relative density; however, low pressure sintering process does not apply to the preparation of Cu-Sn-Bi bearing alloy because it is easy to aggravate the loss of Bi content; while the alloy prepared by the approximate industrialized preparation and sintering process sintered at 850℃ can guarantee the alloy composition with no change, and the Bi phase in the alloy has fine and uniform distribution, and the alloy has good mechanical and tribological properties, and the tensile strength can reach 230 MPa, which showed a typical ductile fracture.Finally, in order to achieve the application of MACu-10%Sn-5%Bi alloys in sliding bearings, approximate industrialized preparation and sintering process was used to obtain Cu-10%Sn-5%Bi bearing strip, the organizational structure and properties have been analyzed compared with industrial Cu-10%Sn-4%Bi bearing strip. The results showed that the Bi phase is more fine and uniform distributed in our bearing strip than the industrial one, while the bonding strength and anti-friction properties is similar to industrial bearing strip, but the wear resistance is better. |
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