Tribological investigations of silicon nitride lubricated by ionic liquid aqueous solutions

Water-lubricated ceramic components are promising material combinations for tribological applications because they are wear-resistant and can exhibit low coefficients of friction under different loads. The aim of the work was to show in model tribological experiments with silicon nitride that the lubricating properties of water can be improved by adding water-soluble ionic liquids. The geometry used and the experimental parameters were selected to approximately simulate a piston ring/cylinder liner contact. We found that the addition of 1% IL tributyl methyl phosphonium acetate[P4441][OAc] leads to a reduction of the maximum friction work by 58% compared to pure water lubrication and even by 96% compared to oil lubricated steel. It was shown that suitable running-in conditions and sufficient cooling by the lubricant at an early stage are important prerequisites for achieving low friction and wear values. In addition, the chemical interaction of water and IL with silicon nitride strongly affects the tribological behavior. As increasing demands on sustainability (green tribology) become more and more important due to environmental aspects, this work provides important insights for the development of novel water-based lubricant systems.