Friction And Wear Properties Of Cu-based Self-lubricating Composites In Aviation Environment

Molybdenum disulfide and graphite both have hexagonal crystal system. Theyhave excellent tribological properties owing to their strong covalent bonding withinthe layers, but weak bonding between the layers. Cu-based self-lubricatingcomposites were fabricated by the P/M hot pressing method under pure argonatmosphere protection. Friction coefficient, wear rate and contact voltage drops ofthe composites were investigated by mechanical wear and electrical wearexperiments. Microstructure, phase of the composites and tribo-films formed on theworn surfaces were characterized by X-ray diffractometer, scanning electronmicroscope and X-ray ptotoelectron spectroscopy analysis respectively.Results show that no chemical reactions occurred among raw materials duringsintering progress. Density, hardness, bending strength and electrical resistivity allincreased with the increasing content of MoS2, while the situation in relativedensity was entirely opposite.Results of mechanical wear experiments show that Cu-G-MoS2composite hadthe best tribological performance in air condition whereas Cu-MoS2compositeoccupied the first place in vacuum and Cu-G-MoS2composite came second.Friction materials used in aerospace should experience both air and vacuumconditions, so Cu-G-MoS2composite is adequate. The strength of the matrix andintegrality of the tribo-films are the key factors in influencing the tribologicalproperties.Results of electrical wear experiments show that tribological behaviors of thecomposites were mainly influenced by existent current. The additional Joule heatdue to the release of current caused the inteneration of surface layer of thecomposites, and inhibited the action of the tribo-films to remain tightly bound tothe matrix which increased the wear rate. The wear rate of the composite withelectric current of10A/cm2and20A/cm2were respectively2.8and3.7times higherthan that without electric current under the same testing conditions. The frictioncoefficients and wear rates of composites in air were lower than those in vacuumdue to the synergistic effect of lubrication from the mixture of MoS2and graphite inair and the limited lubrication properties of graphite in vacuum. MoS2and graphiteplayed roles in tribological properties in common under different testing conditions. Graphite plays a leading role in anti-friction and wear resistance in air, theproportion of graphite in the tribo-film decreased when the current densityincreased. MoS2is relatively dominant under vacuum condition, and the proportionwas little influenced by the current density. Contact voltage drops increaseddisproportionately to the increasing current density.