Abstract
This paper is primarily concerned with the effects of sulfur- or phosphorus-type additives and of the atmosphere on EP lubrication failure as an extension of work reported previously. With a modified stepwise loading procedure, the effects of some EP additives on wear and friction were investigated using a four-ball machine. It was found, from the results of electron probe microanalysis, that the chemical nature of films on rubbing surfaces varied with the atmosphere and with the chemical structure of the sulfur compounds. The nature of the surface films correlated closely with the tribological behavior and may control the lubrication regimes. The less reactive additives had better frictional behavior in air because EHD effects can contribute to the concentrated contact. The transitions observed here are compared with those proposed by OECD-IRG ∗ ∗ The International Research Group on Wear of Engineering Materials, under the auspices of OECD. . The method of evaluation of EP additives is discussed.
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