Synergism of TiO2 and Graphene as Nano-Additives in Bio-Based Cutting Fluid-An Experimental Investigation

The present work aims to investigate the synergetic effect of titanium dioxide (TiO2) and graphene (GnP) nanoparticle additives on the rheological and machining characteristics of biodegradable vegetable oil (rice bran). The rice bran oil has been used in turning of M2 steel using a minimum quantity lubrication (MQL) technique. The effects of varying concentrations by weight (0.5 and 1 wt%) of both mono (rice bran oil/TiO2) and hybrid (rice bran oil/TiO2/graphene) nanofluids have been studied. The rheological studies of both mono and hybrid oils revealed an improvement in the viscosity with an increase in nanoparticle concentration. Furthermore, an improvement in viscosity in hybrid fluids at higher temperatures was observed. The experiments revealed that hybrid nanolubricant shows a significant reduction in tool flank wear and surface roughness by 38 and 11%, respectively, compared to TiO2-based lubricant used alone. The tool wear decreased considerably by about 29 and 32% corresponding to 500 and 1,200 rpm, respectively in the case of hybrid fluid (1 wt% TiO2+graphene) in comparison to the base oil, which considerably enhanced the tool life. Scanning electron microscopy analysis was conducted to study the mechanisms of tool wear at flank faces and crater faces. Chip morphological analysis was performed for the acceptable chips by analyzing the color and structure, depicting the amount of heat generation at the tool-workpiece interface. The results establish that synergism of GnP with TiO2 enhances the tribological properties and hence provides a greener and efficient lubrication methodology.