Comparing tribological behaviors of plasma nitrided and untreated bearing steel under lubrication with phosphor and sulfur-free organotungsten additive

The interactions and synergistic tribological effects between plasma nitrided bearing steel surface and phosphor and sulfur-free organotungsten lubricating additive compared with that of untreated steel were investigated in this paper. The tribological behaviors were examined on a four-ball friction and wear tester. The chemical characteristics of the tribofilms were analyzed by X-ray photoelectron spectroscopy (XPS). The results showed that the obvious synergistic effects of better tribological performance between nitrided surface and organotungsten additive were attributed to WN formed in the tribofilm and a stronger adsorption of organic carbon chains and higher contents of C and W element in the tribofilm.

► The tribological behavior was studied between organotungsten and nitrided surface.
► The organotungsten was a phosphor and sulfur-free additive.
► WN and higher contents of C was formed in the tribofilm on the worn nitrided surface.
► This unique tribofilm provided better anti-wear and frcition-reducing properties.