Surface Morphology
SEM analysis was carried to study the surface morphology of steel balls after the wear tests. Fig. 9 (a and b) and Fig. 10 (a and b) shows the morphology of worn surface of steel balls lubricated by base oil EKE and EKE containing IL (BHI-RA), base oil DOS and DOS containing IL (BHI-RA) respectively. It can be observed that the base oil lubricated surface is quite rough with wide scratches and deep furrowed wear tracks which are signs of mordant wear. Whereas, the surface lubricated with base oil containing IL is smoother with few scratches and wear tracks which is in well accordance to the efficient antiwear behaviour of IL. These results show that a stable tribofilm formed with additive to prevent the direct contact between interacting surfaces (Ing et al., 2012). Fig. 11 (a and b) shows the EDX spectrum of worn surface lubricated with base oil EKE, DOS and base oil blended with BHI-RA (Fig. 11 (c and d)). It can be seen that the surface lubricated by neat base oil EKE and DOS shows iron, carbon and oxygen signals whereas, surface lubricated with IL blended base oil showed additional nitrogen signal. These findings further suggest that the incorporation of nitrogen on the surface provide the protection against severe wear damage.