Enhancing the Lubrication Performance of Steel–Steel Contacts Using a Novel Ionic Liquid Based on Phosphate Ammonium Salt as an Oil Additive

Oil additives are essential for improving anti-wear (AW) properties and durability of mechanical components. In this study, a novel ionic liquid based on phosphate ammonium salt (coded as IL-NPAS) was designed using organic synthesis methods. The high-level objective of this work is to enhance the wear resistance ability of oil-lubricated steels with low-cost additives in terms of materials and manufacturing methods. The IL-NPAS additive was incorporated at concentrations of 0.1 wt% and 0.5 wt% in 150 SN oil, which served as the base oil. Additionally, the commercial oil additive (coded as AW6110) was utilized as a reference to evaluate the effectiveness of the synthesized additive. The frictional behaviour was evaluated with an SRV tribometer at test temperatures of 25 °C and 100 °C. After that, SEM, 3D profilometry, XPS, and TOF-SIMS techniques were employed to show the wear modes and determine the chemical composition of the lubricating tribolayer. Noticeably, the formulated lubricant based on the 0.5 wt% IL-NPAS additive provided AW performance almost identical to the AW6110 additive. The results showed that the 0.5 wt% IL-NPAS additive reduced the coefficient of friction (COF) and improved AW properties by 34–36% and 80–90%, respectively, compared to the 150 SN base oil. Overall, this study holds significant promise for the development of low-cost lubricating oil additives.