Tribological and Rheological Performance of Gasoline Engine Surface Specimens Lubricated with B4C, hBN, HSG, and Hybrid Additive-Containing Oils

In this study, the effect of boron carbide (B4C), hexagonal boron nitride (hBN), holy super graphene (HSG), and hybrid (B4C + hBN + HSG) nano-additives on the tribological performance of SAE 5W-30 gasoline engine oil was investigated on Al-Si-based samples (Al 4032) prepared by cutting from a single-cylinder gasoline engine block. The addition of nano-additives regularly increased the kinematic viscosity; the 63.80 mm2/s (BO) value rose to 68.90 mm2/s at the highest level of B4C and to 70.50 mm2/s in the hybrid oil (≈10.5% increase). The lowest and most stable friction performance was found in the hybrid 0.025 g/25 mL nano-additive oil, which remained between 0.03 and 0.05 during the entire COF test. The EDS mapping and line scan results confirmed the formation of tribofilm by identifying the additive elements (B for B4C, B and N for hBN, C for HSG) in the wear scar, and the presence of increased O elements showed the restricted formation of tribo-oxidation. The results show that hybrid nano-additive oils provide the most effective friction and wear improvement, especially at low concentrations, while at high additive levels, performance does not show a consistent increase due to particle accumulation and third-body effects.