Avocado oil-based GNPs/TiO 2 hybrid nanocutting fluid for sustainable machining of AISI 1045 steel under MQL-CNC milling

This study investigates the thermophysical, rheological, and tribological performance of avocado oil-based nanocutting fluids containing hybrid graphene nanoplatelets (GNPs) and TiO 2 nanoparticles in minimum quantity lubrication (MQL)-assisted CNC milling of AISI 1045 steel. The nanoparticles were dispersed at 0.1, 0.15, and 0.2 wt% by magnetic stirring and ultrasonication. Nanoparticle addition increased the viscosity but raised the thermal conductivity by at most 1.9%, and all fluids retained Newtonian behavior within the investigated shear rate range; the machining improvements were therefore attributed mainly to enhanced lubrication rather than heat conduction. The 0.15 wt% formulation performed best, with the lowest mean cutting temperature (43.7°C), flank wear (VBmax = 0.405 mm), and surface roughness (Ra = 1.24 µm). Under the investigated conditions, the GNPs/TiO 2 nanocutting fluid significantly reduced the cutting temperature and flank wear relative to dry cutting and a commercial coolant, supporting its potential as a sustainable MQL lubricant.