The Effect of Lubricant Additives on Hydrogen Permeation Under Rolling Contact

The multiple roles of a chemical tribofilm in hydrogen uptake from lubricated rubbing contacts

“…The strong interaction between the rapidly forming tribofilm and the metal substrate will cause less metal-metal contact at asperities and fewer active sites to be exposed during rubbing process. The correlation between the tribofilm formation and decomposition rate of the lubricant was already suggested by other researchers [5,8,9]. Both Niste et al [8] and Tanaka et al [9] pointed out that ZDDP tribofilm can prevent hydrogen embrittlement by interfering with the production of atomic hydrogen on the nascent surface.…”

“…They attributed this behaviour to the presence of a complex WS2 tribofilm and its potential to impede hydrogen permeation. Recent publications also reported that, in optimum conditions of temperature, pressure and sliding, the ZDDP-generated tribofilm can hinder hydrogen entry into the steel [9,10]. The potential beneficial effects of DLC coating was also studied by Lu et al [2] and it was found that the coating could prevent hydrogen permeation by reducing friction and wear led to the less chemical composition of the lubricant.…”

Hydrocarbon Lubricants Can Control Hydrogen Embrittlement

“…In the case of a hydrocarbon lubricated tribological contact hydrogenolysis may lead to the formation of a carbonaceous tribofilm over the nascent surfaces (wear track) which act as a catalyst. It has been shown that tribofilm formation on the wear track can attenuate the generation and permeation of atomic hydrogen and therefore prevent HE of bearing steel 1,19 . The cleavage of the hydrocarbon chains could result in a decrease in lubricant viscosity over time.…”

“…One of the most promising solutions to reducing carbon emissions is to use hydrogen as the fuel as its combustion products are water. However, the use of hydrogen is not without its problems which are principally related to its small atomic size which enables it to diffuse rapidly through the lattice of solid materials and cause hydrogen embrittlement in high strength steels, such as those used in typical lubricated rolling element bearings, which are subject to high service stresses [1][2][3][4][5][6] . Indeed, previous studies have shown that the reduction in service life caused by hydrogen diffusion is directly proportional to the amount absorbed 4,[7][8][9] and thus more problems might be anticipated in a hydrogen environment.…”

“…Previous research has shown that the use of additives which lead to the formation of a tribofilm on the wear track can reduce hydrogen damage. The most studied additives have been the conventional antiwear zinc dialkyldithiophosphate (ZDDP) and extreme pressure trioctyl phosphate (TCP) because of their ability to dynamically generate thick and uniform chemical tribofilms which impede hydrogen generation and permeation while simultaneously preventing excessive wear and seizure in the EHD contacts operating in severe conditions (high pressure and temperature) 1,10,11,[16][17][18] . The novel 2H-WS 2 nanoadditized lubricants were shown to achieve a 30% reduction of hydrogen permeation in bearings compared to the PAO base oil, while also controlling wear and generating smoother wear tracks 19 .…”