Effect of lubricant composition and tribological contact conditions on permeation of hydrogen into steel rubbing surfaces

Premature failures of machine elements, such as bearings and gears, in lubricated machines have often been linked to the permeation of hydrogen into contacting surfaces during rubbing. Presence of mobile hydrogen in hard steels is known to lead to embrittlement, and hence shorter fatigue lifetimes of the affected components. Perhaps the best-known system where hydrogen induced failures may be of significance is the drive train of wind turbines. Composition of lubricating oils is a major factor that controls potential generation of hydrogen in rubbing contacts and its subsequent entry into steel. With appropriate understanding, oil formulation may be optimised to mitigate against hydrogen-induced failures by, for example, forming surface tribofilms which can act as barriers that prevent entry of hydrogen into steel surfaces, hence extending the lifetimes of affected machines. The understanding of the relevant mechanisms gained in this project will also be valuable in designing wider infrastructure needed for hydrogen to become an important energy source in our overall energy mix.