The friction and wear, and their inter-relationship, in abrasion of a single crystal of brittle nature

The friction coefficient μ and the mass wear rate M during abrasion of a brittle material in single crystal form (rocksalt, cube face cleavage) are studied quantitatively as functions of the abrasive particle diameter D at load 0.5 kg. μ on emery papers coarse enough to avoid clogging is constant, μ max . This, and the fact that μ max is about the same as for a metal of similar hardness, indicates that μ is determined essentially by the plastic flow properties, and scarcely at all by the extensive brittle fractures which occur in addition to the plastic flow, near the grooves ploughed out by the abrasive particles. The wear, however, is greatly increased by the cracks and fractures. Three types of ( M , μ) relationship are observed, in different ranges of depth of indentation of the abrasive particles. For less than 0.5 μm depth, fracture appears to be practically absent, plastic flow predominates and the ( M , μ) relation is about the same as for metals. At deeper indentations a linear ( M , μ) relation occurs but with greatly increased wear. Finally, at depths greater than 5 μm, the wear rate increases strongly without much further increase in μ, showing the greatly increased spread of fractures around the indenting particles. A modified theory of friction and wear in abrasion of such brittle solids is developed.