Role of Third Bodies in Friction and Wear
Abstract
Friction is usually treated as a two-body problem, in which the two counterfaces move against each other and a "magical" parameter the friction coefficient comes into being. Not so. At some scale, from atomically thin surface films to chunks of wear particles, third bodies play an important role in friction. These third bodies are often born in the sliding contact and sometimes growing up to be wear particles. They might come about because the tribologist intended to lubricate one or both counterfaces, or they might arise simply from atmospheric gases. Either way, they play a far more important role in friction and wear than you would gather from treatments of friction and wear found in the literature. For the past fifteen years, our studies at the Naval Research Laboratory have focused on sliding behavior of "low wear" coatings and surface treatments in concentrated contacts. We have been interested mainly in "how" films transfer to the stationary counterface and "what" compositions and phases of films and third body particles form. Friction and wear tests have been carried out at relatively low speeds, typically 0.1 - 100 mm/s, with sphere-vs.-flat geometries at high normal contact stresses, 0.5 - 1.5 GPa, in unidirectional or reciprocating sliding. Surface topography, chemistry and microstructure are characterized before and after wear tests and, more recently, by in-situ and in-vivo studies; in the latter, we have focused our sights on the contact itself, watching third bodies form and move in the contact and using Raman microscopy to identify compounds in the sliding interface. Although original films wear away, subsequent films can grow if the environment provides a replenishing material (e.g., oxygen) or the sliding contact replenishes transfer films by forming third body reservoirs.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2007
- Accession Number
- ADA462117
Entities
People
- I. L. Singer
- K. J. Wahl
Organizations
- United States Naval Research Laboratory