Friction characteristics of lubricated copper surfaces with controlled asperity sizes

Abstract

The sliding friction behavior of flat copper surfaces with various surface asperity radii, 2.5–300 μm, coated with tin has been investigated as a function of the normal load, temperature, sliding velocity and film thickness. Various surface asperities were produced and controlled by bonding a layer of monosize spherical copper particles to a flat copper surface and then sliding the monolayer against the lubricated flat copper surface. The coefficient of static friction f, at constant temperature and pressure, was found to vary with the lubricant film thickness t and asperity radius R in the manner f = A(t/R) 1 2 +B where A and B are constants which depend on the type of lubricant used. At small loads, less than 0.1 gf per asperity, the coefficient of friction was found not to obey Amonton's law and to increase with any further decrease in both the load and the asperity size. Friction characteristics of the sliding surfaces may be adequately explained in terms of film ploughing and shearing and junction adhesion effects.