Tribological Behaviors and the Lubrication Mechanism of Functionalized Boron Nitride Nanosheet-Containing Fluid for Titanium Alloy Cold Rolling

The hexagonal boron nitride (h-BN) nanosheets were obtained by probe ultrasonication-assisted liquid-phase exfoliation and functionalized with sodium oleate. The tribological properties of functionalized h-BN (f-BN) nanofluid were tested using the four-ball wear test machine. The rolling lubrication performance of f-BN nanofluid was assessed using a four-high cold rolling mill. The maximum nonseizure load of about 637 N was obtained with 0.08 wt % f-BN nanofluid, which increased by 35.3% compared with the based fluid. The minimum average coefficient of friction (COF) of about 0.077 was obtained with 0.05 wt % f-BN nanofluid. The results of cold rolling lubrication tests indicated that the rolling force initially declined and then increased with the concentration of f-BN nanosheets. The lowest rolling force was obtained with 0.05 wt % f-BN nanofluid. In addition, the minimum surface roughness of the cold-rolled plate was 0.1847 μm, which decreased by 88.66% compared with no lubricant. It proved that the addition of f-BN nanosheets to the based fluid can contribute to improving rolling lubrication performance and rolled plate surface quality. In addition, the 0.05 wt % f-BN nanofluid was used as a lubricant that could refine the grains and improve the hardness of the rolled plate. Furthermore, the lubrication mechanisms of f-BN nanofluid were discussed.