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Anti-friction coatings – Edition 2001

■ The lubrication of contact surfaces is a known way to reduce phenomena of wear and tear: to lubricate mechanical systems that operate at ambient temperature, greases or oils are regularly used. These liquid lubricants are often not suitable for harsher environments (vacuum, high or low temperatures, ionising environments, oxidising, corrosive or vibrating environments); their thermal or chemical instability makes them unsuitable for these applications. The use of solid lubricating materials thus needs to be considered: coatings on contact parts considerably increase the life span of mechanical components by reducing friction and wear and tear.

These tri-biological coatings designed to reduce friction and wear between two parts that are in contact with each have a two-layer structure: a layer of hard, anti-wear material is associated with a layer of solid lubricating material, which reduces the friction coefficient. For the coating to be efficient, it is necessary for the normal and tangential forces that come into play during contact not to modify the coating’s dimensions and not to lead to a loss of hold. In the applications concerned, the hold quality of the coating is therefore a key factor.

This survey uses an initial state of the art review on anti-friction coatings performed by Innovation 128 in 1996; it includes the latest developments and feedback from experience in the last four years on an international level. It describes friction and lubricating mechanisms, available depositing techniques, solid lubricating materials (notably self-lubricating composites), latest developments and examples of industrial experience.