Abstract
The friction tests of inorganic bonded composite solid lubricant films (WS2, graphite, BN) were performed in laboratory air and in 10-4 Pa vacuum. The wear traces and transfer films were characterized by scanning electron microscopy (SEM), and Auger electron spectroscopy (AES). Experimental results suggest that when friction tests were conducted in air, graphite plays agoverning role, while in vacuum WS2 plays agoverning role. In case of changing atmosphere from air to vacuum or from vacuum to air, the composite film showed better friction behaviors in vacuum than in air.
Highlights
Graphite, molybdenum disulfide and tungsten disulfide belong to lamella solid lubricants
The endurance life is affected by environment and though the film lasts for 68000 cycles in vacuum, it was less than 750 cycles in air. (b) Graphite film shows low friction coefficient about 0.2 in air with an endurance life of 25000-30000 cycles
The friction coefficient increased at quite an early stage from 0.2 to 0.6 and the endurance life was less than 250 cycles. (c) For BN film, the friction coefficient was 0.6 in vacuum and 0.2-0.3 in air, but in both environments the endurance life were less than 1000cycles. (d) For composite film, the friction coefficient was 0.06 in vacuum and 0.2 in air, the endurance life reached 59000-70000 cycles in vacuum and 2300037000 cycles in air
Summary
Graphite, molybdenum disulfide and tungsten disulfide belong to lamella solid lubricants. The crystal structures of these solid lubricants are such that while the atoms lying on the same layer are closely packed and strongly bonded to each other, the layers themselves are relatively far apart and the bond between them, e.g., van der Waals, are weak. When these lamella solid lubricants are present between sliding surfaces, these layers can align themselves parallel to the direction of relative motion and slide over one another with relative ease, providing low friction[1]. While at low temperature graphite can provide lubrication, BN does so over 500 °C, graphite gets oxidized at high temperature [7]
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