Lubrication by Transferred Films of Solid Lubricants

Experiments are described to determine the lubricating ability of various solid films, particularly graphite and molybdenum disulfide, transferred from a compact to a steel surface. The amount of lubricant transferred depends markedly on the surface finish of the steel, and the most effective films are formed on relatively rough surfaces. In these conditions, bonding between the film and its substrate appears to be primarily mechanical. Determinations of the scuffing load and endurance tests show that replenishment of the lubricant film by continuous transfer to compensate for wear is only possible to a limited extent. With molybdenum disulfide, the film ultimately wears away, but with graphite, failure occurs when the mean surface temperature exceeds about 100 C. The load-carrying capacity of transferred films of molybdenum disulfide is appreciably greater than that of graphite films.