The research aimed at finding an effect of the type and concentration of lubricating additives on the resistance of a tribosystem to scuffing, seizure and pitting (surface fatigue). Lubricating oils of various chemical composition were tested. A base mineral oil was blended with commercial packages of lubricating additives of AW and EP type, at different concentrations. The AW additives contained ZDDP, and EP ones — organic S-P compounds. The tests were performed in two different four-ball testers. One was used to investigate scuffing and seizure at pure sliding friction. The second instrument was employed to test pitting at rolling movement. It is shown that although the lubricating additives improve the resistance to scuffing and seizure, great care must be taken when increasing their content, since at higher concentrations they accelerate pitting. SEM, EDS, GDOES and FTIRM analyses of the worn surface were performed to find the reason.

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