Wear Debris Formation and Agglomeration

Abstract

The hypothesis that one of the primary roles of an effective lubricant is to prevent wear particle agglomeration, thus reduce the plowing of the interfaces by the particles, and lower the frictional force, has been tested through a series of experiments and modeling. The friction coefficient, and the interfacial separation of the sliding surfaces due to entrapped wear particles, were measured on a number of sliding pairs in both dry and lubricated sliding. The results showed that the particle size, even during a single sliding test, did not remain constant but increased as sliding progressed. This increase in the wear particle size was found to be due not to the formation of larger wear particles but to the agglomeration of the small wear particles produced during sliding. The formation of large wear particle agglomerates caused an increase in the amount of plowing and often a concurrent increase in the friction coefficient. When one of the sliding surfaces was textured with undulations, no wear particle agglomeration was observed. The newly formed wear particles simply got entrapped in surface microgrooves and were immediately removed from the sliding interface before their subsequent growth by agglomeration. It was further shown that “good” lubricants prevented agglomeration, thus the friction coefficient remained more or less at the initial low value. Both the dry and lubricated sliding test results are presented and discussed in light of the analytical models based on the plastic deformation of the individual wear particles and the slip-line field analysis of the wear particle agglomerate.

Role of Wear Particles in Scuffing Initiation

“…This difference should be because adhesive force between wear particles and between and contact surfaces are somehow weakened by the lubricant. This is consistent with the suggestion by Oktay and Suh [14] that an effective lubricant can prevent wear particles agglomeration by coating the individual wear particles well thus reducing the strength of the inter-particle bonding. Secondly, the position of particle agglomeration is different under the two conditions: in the lubricated condition wear particles are agglomerated at both the sides of the contact area.…”

The effects of subsurface deformation on the sliding wear behaviour of a microtextured high-nitrogen steel surface

“…However, as the particle size rises or extensive agglomeration takes place, the friction coefficient increases again. Studies with undulated metal surfaces showed that friction values remain low when debris is entrapped within depressions [35]. In the present investigation it was shown that electrochemically microtextured surfaces have the potential to lower wear and prevent agglomeration on the articulating surfaces by fixing wear particles in the microscopic topography.…”

Temperature dependent friction and wear of magnetron sputtered coating TiAlN/VN

“…In the sliding wear of metals [31], after the generation and agglomeration of wear particles in the initial wear, the severity of sliding friction depends strictly on the adhesive interactions of the wear debris. Therefore the role of a lubricant is related to the breaking or weakening of the interfacial bonding.…”