Foamed-metal reinforced material: tribological behaviours of foamed-copper filled with polytetrafluoroethylene and graphite

Abstract

A novel foamed copper based (FCB) composite is developed as a rubbing pair material. The composites consist of the foamed copper and solid lubricants, such as polytetrafluoroethylene and graphite. Four kinds of FCB composites were fabricated by vacuum filtration, compression moulding, and sintering process in an orderly manner. The thermal and electrical conductivities and tribological properties of the new composites were investigated. Because the interconnected metal skeletons have been embedded in the polymers, the FCB composites possess excellent thermal and electrical conductivities, including nice self-lubricating property. The friction and wear properties were investigated on an M-2000 friction and wear tester. An electric field was imposed between the sample and ring to monitor the tribo-chemical reaction and formation of transfer film by means of ‘contact resistance’. The measurements of friction temperatures were carried out by means of three thermocouples embedded in the material. The friction tests show that the friction coefficients of the FCB composites decrease almost monotonically with the increase of graphite content under different conditions; and the wear rates decrease overall compared with that of the homologous polymers, more obvious especially under severe conditions. The optical microscope, SEM, and XPS were adopted to study the worn surface morphologies and the transfer films. The main wear mechanism of the new composite is a three-body abrasion, caused and promoted by the plastic deformation, abrasive wear, and fatigue spalling. The oxidation of copper is the dominant chemical processes which occurred during the sliding process.