Transitions in the Friction and Wear of Carbons and Graphites Sliding Against Themselves

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Abstract
The friction and wear properties of various carbons and graphites have been measured during sliding against themselves in air. Many materials exhibit sudden and large increases in both friction and wear at a critical combination of load, speed, and temperature, and the effects are most pronounced for electrographites and natural graphites. The sliding conditions at the transition are associated with a critical temperature of the contacting asperities, and the magnitude of this temperature, approximately 150–185 C for graphitic materials, has been estimated both directly and by application of flash-temperature theory. The phenomena accompanying the transitions are very similar to those occurring during dusting of carbon brushes at high altitudes, and a similar explanation is invoked in terms of the adsorption of water vapor and oxygen. The critical combinations of loads and speeds required to initiate the transition are much more severe than those normally encountered during the operation of carbon brushes and bearings.