Synergy Study Between a Lubricant Oil Layer and a Microstructural Graphite to Reduce Friction and Wear of a Thermally Modified Low-Carbon Gray Cast-Iron Cylinder Liner

Abstract

The results of a sliding wear tests on base and thermal treated gray cast iron (GCI) samples from internal combustion engine cylinder liner are reported here for dry and lubricated conditions. A thermal treatment was applied to samples of 10 x 10 mm to avoid the effect of residual stress and to obtain the microstructure of interest. Tribological tests were carried out up to 27000 cycles at room temperature. A frequency of 15 Hz, a stroke amplitude of 6 mm, and a maximum contact pressure of 1.12 GPa were selected. Under the unlubricated settings, a noticeable decrease in friction coefficient and specific wear rate are attributed to the appearance of irregular graphite nodules in the heating–quenching process. The significance of thermal treatment applied to low carbon cast iron in the derived self-lubricating function and its synergistic role with the oil lubricant is discussed. In this context, this work illustrates, for the first time, how the change in the morphology from flake graphite to irregular nodule graphite positively determines the reliability of gray casting irons.