Anisotropy in the mechanical properties of lamellar solids and its effect on wear and transfer

Abstract

Experiments have been made to determine the degree of anisotropy in mechanical properties of lamellar solids, such as graphite, MoS 2, mica, PbI 2, etc. Radioactive measurements of the wear of copper sliding against compacts of lamellar solids, together with qualitative assessment of surface damage on other metals, show that many of the solids are intrinsically abrasive. The amount of wear and surface damage depends on the relative maximum hardness of the solid and the metal and, in addition, on the extent to which the lamellar solid acquires a preferred orientation during sliding. The maximum hardness of MoS 2, for example, is 7–8 Mohs. It is suggested that embedding of suitably oriented crystallites of a lamellar solid into metal surfaces is a major factor in the formation of transferred films of the solids. Measurements of the endurance of transferred films of various solids deposited on metals of different hardnesses show that endurance increases as the hardness of the substrate metal decreases. In the particular experimental conditions used (relatively light loads and low speeds) there is no evidence that chemical interactions play a significant role in the bonding of a solid lubricant film to its substrate.