The Importance of Temperature in Generating ZDDP Tribofilms Efficient at Preventing Hydrogen Permeation in Rolling Contacts

Abstract

ABSTRACTHigh-strength steels are particularly susceptible to hydrogen embrittlement and therefore rolling element bearings can experience premature failure that drastically reduces their operation life. Some lubricant additives can prevent this by generating protective tribofilms during operation. This study investigates the effect of temperature on the growth of zinc dialkyl dithiophosphate (ZDDP)-generated tribofilms and the relationship with the permeation of hydrogen in the substrate.Rolling contact tests were conducted using ZDDP at 333, 363, and 393 K and the concentration of hydrogen was measured after the tests. It was found that low temperatures inhibit the reactivity of the additive, leading to an inadequate coverage of the surface that allows dissociation and permeation of hydrogen in the sample. Higher temperatures induce uniform films in the contact, although excessive temperatures can promote unnecessary wear of the substrate. An optimum temperature can balance the two main processes occurring in the contact related to the reactivity of the additive: the growth of a protective film and the corrosive wear of the material.