Tribochemical behaviors of phosphite esters and their combinations with alkyl amines

•Investigating the differences of tribological performance between phosphite ester and their combinations with alkyl amines.•The combination of SEM and EDS was used to investigate the worn surface morphology and detect the element distributions and content on the steel surface.•The chemical compositions of the thermal films and tribofilms were characterized by TEY P L-edge and FY P K-edge XANES spectroscopy.•A phosphate and polyphosphate tribofilm was formed after rubbing times of even 10s, and being formed completely after rubbing times of 10min.•Phosphite ester forms short-chain polyphosphates, and ammonium phosphite produces medium-chain polyphosphates in the tribfilm. The tribochemical behaviors of dioctylphosphite ester and ditetradecylphosphite ester together with their corresponding combinations with alkyl amines were studied. The results of tribological evaluations showed that the phosphite ester with long alkyl chain exhibited better antiwear performance but worse extreme pressure property than that of the phosphite ester with short alkyl chain. The combinations showed better antiwear performance but worse extreme pressure property than their corresponding phosphite esters. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to investigate the worn surface morphology and the content as well as the distribution of active elements. It can be found that the prorupt edges of worn surface are enriched with phosphoric-oxygenic compounds and less phosphoric-oxygenic compounds were detected in the valley. X-ray absorption near-edge structure (XANES) spectroscopy was employed to explore the chemical nature of the worn surface. The results show that a tribofilm composed of phosphates and polyphosphates is formed on the worn surface. Furthermore, the tribofilm is generated even in a rubbing of 10s and is formed completely after 10min rubbing.