Role of additive concentration in slow-speed sliding contact under boundary lubrication conditions

The adsorption model for boundary lubrication was proposed considering the variations of additive content with sliding distance. With surface roughness and wear debris caused by the adhesive wear of the oxide layer, a mass conservation of additive dissolved in lubricant was established. Any rise in surface temperature due to sliding friction was ignored for this study’s purposes. It was found that the additive concentration decreased rapidly with sliding distance because wear particles adsorbed and consumed the additives. This reduction of the additive concentration raised the friction coefficient by reducing the surface area protected by the adsorption layer without any temperature effect. This analysis model was verified by comparing it with the test results of existing literature. Because this model is effective at extremely low-speed conditions, these results can help explain the failure mechanism in room-temperature, lowspeed boundary lubrication.