Optimization of the Tribological Behavior of TiO₂ Nanolubricants: Experimental Design and RSM-Based Analysis

This study optimizes the tribological performance of ductile cast iron lubricated with SAE 10W-40 engine oil infused with TiO2 nanoparticles. Nanoparticles were synthesized via the sol-gel technique and dispersed at 0.1-0.4 wt.% concentrations without surfactants. A pin-on-disk (ASTM G99) test rig was used to evaluate the influence of nanoparticle concentration, applied load (13.83-124.15 N), and sliding speed (0.05-0.26 m/s) on the coefficient of friction (COF) and disc weight loss. Response Surface Methodology (RSM) with a Central Composite Design (CCD) was employed for experimental design, and ANOVA was used to evaluate parameter significance4. The results indicated an optimal concentration of ~0.2 wt.% TiO2, achieving up to a 42% reduction in weight loss and a 36% decrease in COF relative to the base oil. Applied load exhibited the most significant effect on both responses. Nanoparticle characterization (FESEM, XRD, EDS) confirmed their nanostructure, crystallinity, and purity. Surface analysis of worn specimens indicated smoother wear tracks and tribofilm formation, demonstrating the efficacy of TiO2 nanolubricants for friction and wear reduction in ductile cast iron under boundary and mixed lubrication regimes.