Different compositions of graphene oxide (GO) and detonation nanodiamond (DND) nanoparticles with API CH-4 engine oil were tested on a reciprocating wear tester at high contact pressure. Significant reductions in friction and wear were observed. Wear surfaces were characterized by a 3D profiler, scanning electron microscopy and energy-dispersive X-ray spectroscopy to determine the surface topography, film build-up composition, mechanism of nanoadditive-assisted friction reduction and wear reduction characteristics. The wear tests indicated that the original engine liner segments containing surface texture with oil retention potential significantly lose their micropeaks and valleys during the test. Even though the surface texture got disturbed, the presence of nanoadditives in the lubricant led to a reduction in the coefficient of friction. Considerable reduction in the roughness level of the wear track associated with the use of a nanolubricant was also explored through the 3D profiler analysis. The surface roughness of the wear track produced while using a nanolubricant with 0.5 mg/l of detonation nanodiamond nanoparticles was 66% lower than the roughness of the wear track obtained with the base oil. The nanolubricant suspended with 1 mg/l detonation nanodiamond nanoparticles achieved a lower coefficient of friction earlier and a combination of detonation nanodiamond and GO at 0.5 mg/l concentration achieved the lowest coefficient of friction and wear at the end of the test duration.
This work investigates the formation, endurance and rupture of tribofilms on a honed engine liner subjected to boundary lubrication in a reciprocating Tribometer. Study focuses on the exploration of synergistic effect between ZDDP additive in the oil and two distinctly shaped nanoparticles, Graphene oxide (GO) and detonation nanodiamond (DND), in improving the characteristics of tribofilm. Tested samples were examined by scanning electron microscope and energy dispersive X-ray. The results indicated that the addition of nanoparticles to the base oil with ZDDP accelerates the tribofilm-formation. Although fully developed tribofilms were obtained with both the nanoadditives, the DND based tribofilm was more durable under the dry running conditions. However, P-rich tribofilm formed in the presence of GO showed self-mending characteristics. Nanoindentation studies on the wear tack revealed a 12% increase in elastic modulus and 23% increase in average hardness for the sample tested with DND compared to that of base lubricant.
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