Vapor Deposited Gold Thin Films as Lubricants in Vacuum (10−11 mm Hg)

Abstract

Gold thin films of 1800 Å to be used as lubricants were vapor deposited on Ni, Ni-Cr, and Ni-Re substrates. Strong bonding (adhesion) and durability between the film and substrate were found to be essential when thin films are used as a lubricant. Factors that were investigated included the selection of the film and substrate material. Strong durability of the thin film is directly related to the type and structure of the interfacial region. Two methods of substrate preparation prior to vapor deposition were investigated: (1) mechanically polished surface and (2) electron bombarded surface. Gold was vapor deposited on the mechanically polished surface at room temperature and on the thermally etched surface at an elevated temperature approximately (800 °F). Strength and durability of the films were investigated in sliding friction experiments with a hemispherical niobium rider sliding on the films at a velocity of 5 ft/min. Results obtained in these friction experiments indicated that the film endurance life was considerably better on the thermally etched surface. This increased film durability with the thermally etched surface is believed to be owing to the formation of a diffusion type interface between the film and the substrate. Because of the disregistry at grain boundaries, a higher rate of diffusion and preferential trapping in and around the grain boundaries occurs, with these regions acting as lubricant reservoirs during the friction experiments.