High Temperature Tribological Properties of Cu-2Ni-5Sn-Graphite-PbO Self-Lubricating Composites

Cu-2Ni-5Sn-Graphite-PbO self-lubricating composites were prepared by powder metallurgy. The microstructure and mechanical properties of the composites were examined by using X-ray diffraction, scanning electron microscopy and a universal material testing machine. And the tribological properties of the composites were investigated using a pin-on-disc friction testing configuration from room temperature to 500 ℃. The results indicate that the best comprehensive tribological properties were obtained for graphite+PbO composite of 8%. The addition of Ni enhanced the mechanical properties of the matrix. The friction coefficient of composites remained stable with the increase of temperature. The wear rates of the composites firstly slightly increased and then sharply increased with increasing temperature. At room temperature, the lubricating film was composed mainly of graphite and the main wear mechanism is mild plastic deformation and local peeling off. At 300 ℃, the improved tribological properties of the composites were attributed to the formation of a dense and lubricious film of graphite, PbO(Fe₂O₃)₆ and Cu₂O, the main wear mechanism was plastic deformation, local peeling off and adhesive wear. At 500 ℃, the composite lubricating film was composed of PbO(Fe₂O₃)₆, graphite, Cu₂O and CuO, and the main wear mechanism was the peeling off of the matrix of graphite surrounding area, peeling off caused by the plastic deformation and oxidative wear.