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This article describes the effect of polymer additives in lithium greases on performance and boundary layers of high-speed angular contact ball bearings. High-speed test rigs were used to run grease life tests utilizing five lithium grease variants that were derivatives from the same basic grease composition. While one was used in its plain state, the other four were blended with polymer additives. The test runs showed different operating characteristics of the greases with total service lives (L 10 ) ranging from 139 to 1010 h. Furthermore, the operating temperatures of the greases varied by up to 11 • C. After test run completion, surface hardness was measured on the raceways using a nanoindentation system with a triangular diamond pyramid Berkovich tip and an applied force of 1.5 mN. As a reference, a 'virgin' bearing was studied having not yet been in contact with grease. Thereafter, measurements were performed on samples that had been in contact with the five described greases. It is shown that polymer additives indeed can influence the properties of boundary layers, thereby affecting the bearing's service life and friction.

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