Wear mechanism of steel materials oxide form conversion at the friction interface conducted by lubricants containing varying hydrogen

Hydrogen internal combustion engines are up-and-coming power devices in the current energy field. However, engine lubricants are prone to contact with hydrogen and water vapor during operation, and the impact of these gases on the tribological properties of the lubricants has not yet been clearly studied. In this work, the tribological performance and mechanism of emulsified lubricants with varying hydrogen content were investigated. The results demonstrated that the width and the depth of the wear track on the GCr15 steel blocks decreased by 86.8% and 80.4%, respectively, as the volume ratio of hydrogen gas to oil increased from 0 to 100 vol%. The conversion of complete oxide layer (FeOOH–Fe₂O₃) and composite oxide layer (Fe–FeO–FeOOH–Fe₂O₃) at the frictional interface was proposed as the wear mechanism, and this mechanism was confirmed utilizing optical microscopy, contact three-dimensional (3D) profilometry, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). A complete oxide layer lubricated by pure oil results in severe adhesive wear at the friction interface, whereas a composite oxide layer under 80–100 vol% H₂/oil emulsified lubricants was discovered to reduce oxidation corrosion and wear. The characteristics of this wear mechanism can be applied to reduce wear in tribo-pairs and lubricant designs of hydrogen internal combustion engines.