Wear and mechanical properties of sintered copper–tin composites containing graphite or molybdenum disulfide

Abstract

Copper-based sintered composites produced by powder metallurgy processes are now widely used in tribological engineering parts, e.g. bearings and bushes. Also composites based on copper–tin alloys containing a solid lubricant have been developed as self-lubricating materials under extreme conditions of load, atmosphere and temperature. It is well known that the addition of graphite serves to reduce friction and wear in copper–tin alloys. However it should be noted that the addition of graphite or molybdenum disulfide (MoS 2) has an adverse effect on the composites’ mechanical properties. In this paper, the lubricant graphite and MoS 2 powders were coated with Cu to reinforce their bonding to the Cu particles in the composites during sintering. The hardness, microstructure and bending strength of the sintered specimens were examined. The friction and wear properties of the materials were estimated by a cylinder-on-plate wear machine under dry conditions at room temperature in air. Although mechanical properties of the composites decreased with increasing amount of added graphite or MoS 2, the use of Cu-coated lubricant powders improved the bending strength. Graphite was very effective in reducing the wear and friction of the composites. Particularly, the 40 vol.% graphite composites showed a very low coefficient of friction of 0.15. Furthermore, the wear rate of the Cu-coated graphite specimens was much lower than that of the uncoated graphite specimens. By contrast, the wear rates of the MoS 2 composites increased considerably with the amount of MoS 2 addition. This behavior is thought to be due to the absence of MoS 2 and the presence of brittle CuMo 2S 3 compounds in the sintered composites.