Atomic Layer Deposition of Tungsten Disulphide Solid Lubricant Nanocomposite Coatings on Rolling Element Bearings

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Atomic layer deposition (ALD) has the potential to provide highly conformal coatings with precise control of thickness. This article describes the application of ALD nanocomposite containing ZnF2 in WS2 matrix solid lubricant coatings on fully assembled rolling element bearings. The torque behavior of the coated bearings was studied during oscillatory contacts and after exposure to vibration. The coatings exhibited a hexagonal layered structure with predominant preferentially orientated (002) basal planes. These basal planes when sheared imparted very low running torque values of ∼ 0.5 mN· m in dry nitrogen. The outer race, inner race, and ball surfaces showed WS2 transfer film protection on the native coating necessary to achieve low torque in dry nitrogen. Structural (re)ordering of the basal and prismatic planes with multiple random and branched orientations was observed through the thickness of the transfer films. There was no evidence of uniformly aligned c-axis perpendicular-orientated basal planes on the transfer film surface. The unique advantages of ALD to apply solid lubricant coatings on rolling elements of fully assembled miniature bearings are compared with conventional solid lubrication techniques.