Investigation of tribological properties of environmentally friendly ionic liquids as a potential lubricity improving additives for water-based lubricants

Purpose This paper aims to investigate the tribological properties of two protic ionic liquids used as lubricity-improving additives in the water. Their concentration was optimized for different metal friction pairs including bearing steel, stainless steel and aluminum alloy. Design/methodology/approach In this study tribological properties were investigated by using a ball-on-plate reciprocating tribometer. Three different friction pairs were selected: bearing steel-bearing steel; bearing steel-stainless steel; bearing steel-aluminum alloy. To optimize the concentration of investigated protic ionic liquids four concentrations were selected. Wettability was investigated using the droplet method. The corrosiveness of additive-loaded water was investigated using the iron chip method. Findings The results show that by using protic ionic liquids the lubricity of water could be greatly improved. However, the friction pair material and additive concentration play a significant role. The positive tribological effect was attributed to the polarity of the additive molecule which tends to form an adsorption layer. The polarity of molecules also leads to better surface wettability. It was also found that both investigated protic ionic liquids can improve the anticorrosion properties of water. Originality/value To the best of the authors’ knowledge, this is the first study to present a complex investigation of tribological properties of two protic ionic liquids as additives in the water. In this case, three different metal friction pairs and four additive concentrations were investigated. The results could be interesting to those who are working in the field of water-based lubricants and luck for multipurpose lubricity-improving additives.