Thick Antiwear Films in Elastohydrodynamic Contacts. Part I: Film Growth in Rolling/Sliding EHD Contacts

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Abstract
It has been previously reported in the literature that a particular, unnamed, phosphonate antiwear additive can enhance elastohydrodynamic film thicknesses on rolling metal surfaces at elevated temperatures. In this paper, several different pure phosphonate additives have been prepared and their performance in rolling contacts has been studied. All the phosphonates tested formed thick films from base oil solution in rolling EHD contacts. The rate of film formation varied with the alkyl or aryl groups present and with the temperature but, in some cases, films started to form at room temperature. These films grew steadily with running over several hours, to reach thicknesses of more than one-half micron, augmenting the normal elastohydrodynamic films by this amount. Further studies have demonstrated that these thick antiwear films can withstand up to 10 percent sliding and are formed in the presence of other additives. The implications of the phenomenon of thick antiwear films as a means of increasing specific film thickness in elastohydrodynamic lubrication are discussed.