Micropitting Performance of Glycerol-Based Lubricants Under Rolling-Sliding Contact Conditions

There is a high demand for environmentally friendly lubricants in order to support a transition to sustainable transport and manufacturing since conventional mineral oils derived from fossil sources are inherently harmful for the environment. Glycerol aqueous solutions have the potential to be used as environmentally friendly base fluids, due to their high solubility in water, and non-toxicity. In this investigation a micropitting test rig (MPR), was used to study the friction, wear and micropitting behaviour of Glycerol-based lubricants in a rolling/sliding contact. Micropitting and wear profiles were analysed through optical profilometry, and the morphology and evolution of micropits were studied trough scanning electron microscopy (SEM). The results showed that the steel-steel contact lubricated with a Glycerol-water-glycol lubricant reduced mild-wear, promoting micro-pitting as a main failure mode at low sliding levels compared to a commercial fully formulated gear oil. It was also shown that friction was significantly lower for the Glycerol-water and Glycerol-water-glycol lubricants which is mainly attributed to an effect of a low pressure-viscosity coefficient.