Self-repairing Effects of Natural Mineral Powders as Lubricant Additive on Steel Tribopairs

An admixture of mineral powders were prepared using ultrafine mechanical grinding process. The self-reconditioning effects of the as-prepared powders as oil additive on carbon steel tribopairs were evaluated by employing a RFT-Ⅲ reciprocating friction tester. Moreover, the worn surfaces and cross-section were characterized by means of scanning electron microscope (SEM), energy dispersive spectroscope (EDS) and Nano indenter. The mechanisms for friction and wear reducing properties were discussed accordingly. Results indicate the mineral powders exhibit excellent tribological and self-reconditioning properties as oil additive. The friction coefficient decreased by 55.1% compared with that of the base oil. And the wear rate of the upper and lower specimen also decreased by 85.7% and 97.6%, respectively, in comparison with those of the base oil. The complex physicochemical actions occurred among the powders and the tribosurfaces, which induced the formation of a continuous and uniform multi-apertured oxide self-reconditioning layer on the tribosurface. The layer with a mean thickness of 0.72 um shows smooth and mainly consists of Fe, C and O, which possesses higher mechanical properties and contributes to the effective decrease in friction and wear of the tribopair.