Graphene Nanoplatelets-Assisted Minimum Quantity Lubrication in Turning to Enhance Inconel 718 Surface Integrity

Inconel 718 is regarded to be a difficult-to-cut nickel alloy due to its low thermal conductivity, high hardness, and chemical reactivity with tool materials at high temperature, which, overall, cause the generation of extremely high temperature at the cutting edge, contributing to deteriorate the surface quality of the machined workpiece. With the aim of improving the alloy machinability, the present paper evaluates the effect of Minimum Quantity Lubrication (MQL) on the turning performances of Inconel 718 compared to dry and flood lubrication conditions. In particular, for the first time, the feasibility of using graphene nanoplatelets as additives to a vegetable oil to form MQL mist is assessed. After having defined the optimal concentration of two graphene nanoplatelets of different size, the nanofluids were prepared and their stability as a function of time was assessed; afterwards, they were characterized by means of viscosity and specific heat capacity measurements as a function of temperature. The cutting performances were evaluated in terms of surface integrity and chip morphology. Results showed that the use of the nanofluid with the lowest graphene nanoplatelets size provided the best surface integrity compared to the ones obtained when using just MQL without any additive and standard lubricating conditions.