| Summary: | The majority of rolling bearings are made from steel due to its suitable mechanical properties. It has been demonstrated that hydrogen evolution from lubricated contacts significantly shortens the steel fatigue life. Significant efforts have been made so far to understand the mechanism of hydrogen-induced failure. However, the failure mechanism is complex and a conclusive theory has remained unknown. The main aim of this study is to develop a novel method, based on the modified Devanathan-Stachurski technique, to experimentally assess hydrogen intrusion into the steel. This new technique enables the study of the hydrogen source in a lubricated contact and the rate of its permeation into the steel. The hydrogen intrusion from various lubricants has been evaluated at both room temperature and high temperature. The effect of water contamination, anti-wear and friction modifier additives in poly-alpha-olefin base oil on tribologically-induced hydrogen uptake were investigated. The results suggest a significant influence of water on hydrogen intrusion. The ZDDP anti-wear and MoDTC friction modifier could reduce hydrogen uptake by forming a uniform tribofilm. On the other hand, the hydrogen permeation is promoted by ZDDP additive when the tribofilm is patchy. This is speculated to be due to the ZDDP decomposition products acting as poisonous agents for recombination of hydrogen atoms. The results indicate that water contamination is more detrimental in presence of ZDDP additive in the lubricant. The study shows that hydrogen is liberated from decomposition of hydrocarbon molecules. The liberation of hydrogen is tied to the rubbing process. The surface rubbing forms a nascent steel surface with active sites by removing contaminants and surface oxide layer. This fresh metal surface catalyses the lubricant decomposition process. It also reveals that hydrogen permeation rate is higher when the load and sliding speed are higher mainly due to the higher wear rate.
|
|---|
