Wear mechanism of Al–Si alloy impregnated graphite composite under dry sliding

Abstract

The Al–Si alloy impregnated graphite composite containing a high content (56 vol.%) of graphite has a good self-lubricating performance in moist air under dry sliding. In this paper, pin-on-disk type wear tests of the composite in contact with bearing steel were conducted in various gas environments to investigate the wear mechanism under dry sliding. The composite exhibits a decrease in wear at high loads in moist air. The wear rate is very high at low relative humidity (RH), decreases with increasing RH to a minimum at middle RH, and increases slightly at higher RH. The wear rate in moist argon is approximately equal to one-third of the wear rate in moist oxygen. At the RH for the minimum wear, the wide, compacted films consisting of graphite and metallic wear particles are formed on the disk sliding surface due to smearing of the particles. These films prevent the sliding surfaces from metal-to-metal contact. A pin-lifting phenomenon is observed in the early stage. The entrance of wear particles onto the contact surfaces causes the pin lifting, leading to an apparent decrease in wear. Models of the wear mechanism are proposed. For no pin lifting, the pin undergoes adhesive wear due to the breakdown of coarse films. For the pin lifting height ( h) lower than 5 μm, since the load is partly supported by a small amount of wear particles on thin films, abrasive wear occurs due to hard oxide particles. For h > 5 μm, many wear particles support the load on the compacted films, and thus, the pin surface is in rolling or sliding contact with the wear particles resulting in a decrease in wear rate.