Effect of temperature on tribological behavior of L–proline–based green deep eutectic solvents for Ti6Al4V interfaces: A study of novel potential lubricant

Abstract

This study aims to develop a novel, eco-friendly lubricant engineered to meet antiwear requirements, reduce energy consumption, and improve performance reliability. A series of deep eutectic solvents (DESs) was successfully synthesized using a facile, one-step approach by combining eco-friendly L-Proline with diols and two distinct carboxylic acids as hydrogen bond donors. The resulting DES lubricants exhibit favourable physicochemical properties and excellent lubrication performance. Notably, the L-Proline /Oxalic acid DES demonstrates superior lubrication performance, resulting in a substantial decrease in both friction (?46–78 %) and wear volume (?61–91 %) compared to PEG 200 and choline chloride/urea across all tested temperatures. Furthermore, in-depth analysis of the worn surfaces reveals the formation of a tribo-chemical film derived from L-Proline based DESs, consisting of hydrocarbon (CxHy), oxy metal nitride (Ti-N-O) fragments, along with titanium oxide/hydroxide-rich layer. This film plays a vital role in delivering effective lubrication for titanium alloy surfaces. These findings pave the way for designing eco-friendly, high-performance lubricants for sustainable lubrication practices. © 2025 Elsevier Ltd