Effects of the physicochemical properties of different nanoparticles on lubrication performance and experimental evaluation in the NMQL milling of Ti–6Al–4V

Processing of Ti alloy is often accompanied with large frictions and high temperature. Nanofluids prepared by adding nanoparticles show good lubrication performance due to the excellent antifriction and antiwear of nanoparticles. The physicochemical properties of nanoparticles are important factors that influence the lubrication performance of nanofluid minimum quantity lubrication (NMQL). An experimental study on Ti alloy (Ti–6Al–4V) milling was conducted to explore the lubrication performance of minimum quantity lubrication (MQL) using different nanofluids. Cottonseed oil was used as the base oil, and the tribological properties of several typical nanoparticles (i.e., Al2O3, MoS2, SiO2, carbon nanotubes, SiC, graphite) were studied. The lubrication performance was evaluated by milling parameters, including milling force, surface roughness (Ra, RSm, Rmr), friction coefficient, microstructures of debris and workpiece surface, and energy spectra of the workpiece surface. Results demonstrated that the milling process based on Al2O3 nanofluid achieved the minimum milling force and friction coefficient, whereas the milling process based on SiO2 nanofluid had the minimum surface roughness value (Ra). Furthermore, the physicochemical properties of nanoparticles and the viscosity of nanofluid were analyzed. Spherical Al2O3 and SiO2 nanoparticles improved the lubrication effect of base oil mostly. The Al2O3 nanoparticles exhibited high hardness, which was conducive to reducing milling force. SiO2 nanofluid demonstrated high viscosity, which could improve workpiece surface quality.