Comparing tribology properties of halogen-free ionic liquid, halogen-containing ionic liquid, and PAO 10 lubricants for steel–Al2024 friction contact at room temperature and high temperature

Halogen-free, N/P-containing ionic liquid (NP-IL) was synthesized by combining bis-quaternary ammonium cations with phosphate ester anions and were compared to polyalphaolefin 10 (PAO 10), and a halogen-containing IL (BMIMPF6). The corrosive properties of the NP-IL, BMIMPF6, and PAO 10 lubricants were evaluated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The corrosion performance tests show that NP-IL has better corrosion resistance than that of BMIMPF6 due to its halogen-free characteristics. The tribological performances of NP-IL, BMIMPF6, and PAO 10 were evaluated by Optimol SRV-V oscillating friction tester. The lubricant mechanism of NP-IL was evaluated using SEM, EDS, X-ray photoelectron spectroscopy (XPS), and by time-of-flight secondary-ion mass spectrometry (TOF-SIMS). From the results, the NP-IL was found to be a suitable lubricant for steel–Al2024 friction contacts. During friction, the IL forms a surface-protective film thought tribochemistry, which contributes to reduce-friction (RF) and anti-wear (AW).