Tribological performance of copper matrix composites under dry and wet conditions

Copper mat rix composites were prepared through powder metallurgic technique. The relationship between speed and pressure of friction and the friction and wear properties of the materials were studied on a pin-on-disk tester in the pressure range of 0. 5～1. 2 MPa under dry and wet conditions. The results demonstrate that thmajor factors affecting the performance are the nature of loading and the state of third bodies. For dry fiction, whe the speed is low, the f riction force is close to static. Such loading allows the third bodies to stay in a porous state increases the level of engagement of asperity, and results in a higher friction coefficient. As the third bodie compact, they provide more lubricating effect, which attenuates the mechanical clenching of asperity, and lowers the friction coefficient as well as wear of the materials. At high speed, hard particulates on the friction surfaces are more likely to be smashed due to impacts among the micro-rises. The broken hard particulates disperse and harden the friction surfaces, causing an increase in the friction coefficient. The friction pressure affects the high speed friction properties significantly because the heavy loading intensifies the deformation and damage of the friction surfaces. Under wet conditions, the effects of flow and lubrication of the water film in lowering the friction coefficient and reducing the wear rate are apparent only at low speed and low pressure. At high speed and high pressure evaporation at elevated temperature and centrifugal action break the water film and consequently the friction and wear properties of the friction materials are similar to those of dry friction.