Ti6Al4V titanium alloy is widely used in aerospace, biomedical, and automotive applications; however, its low thermal conductivity and high chemical reactivity generate excessive heat and rapid tool wear during machining, deteriorating surface integrity and tool life. Although nano-reinforced mineral and synthetic cutting fluids have shown performance benefits, sustainable vegetable-based alternatives remain insufficiently explored. In this study, sunflower-oil-based hexagonal boron nitride (hBN) and silicon dioxide (SiO2 ) nanofluids were comparatively evaluated under Minimum Quantity Lubrication (MQL) turning conditions. The nanofluids were prepared at 0.5 and 1 vol% and characterized through dynamic viscosity and thermal conductivity measurements conducted at two different temperatures. Increasing temperature reduced viscosity by similar to 46% and increased thermal conductivity by similar to 13% for all fluids. Nanoparticle addition caused moderate viscosity rises for hBN (8-14%) but markedly higher increases for SiO2 (33-46%), while thermal conductivity improved by similar to 6% and similar to 3%, respectively. Although SiO2 exhibited superior long-term dispersion stability, its higher viscosity was associated with limited machining improvements. Machining performance was assessed using cutting zone temperature (T: 390-225 degrees C), surface roughness (Ra: 1.165-0.414 mu m), and flank wear (Vb: 0.479-0.224 mm). Grey relational analysis indicated that 0.5% hBN-MQL reduced T, Ra, and Vb by 41%, 65%, and 45% compared with dry condition, achieving the highest overall grade (0.90), and these results were validated by confirmation experiments. Overall, the low-concentration hBN nanofluid, whose dispersion stability was additionally confirmed by short-term Dynamic Light Scattering (DLS) measurements, provided the best balance between heat transfer and lubrication, offering a sustainable and high-efficiency solution for machining Ti6Al4V.