Sustainable turning of Inconel 718 nickel alloy using MQL strategy based on graphene nanofluids

Nickel-based alloys are classified as difficult-to-cut metals due to their low thermal conductivity and strength even at high temperatures. The crucial challenge when turning these alloys is the obtainment of a high surface integrity since they are often used in critical applications like aerospace and oil and gas ones. This is usually fulfilled using cutting fluids that may lead to ecological and health-related issues as well as increase of the production costs. In this context, the paper evaluates the feasibility of sustainable turning of the Inconel 718 alloy using the minimum quantity lubrication strategy based on graphene nanofluids. Graphene nanoplatelets of two sizes, namely 5 μm and 15 μm, were used as additives to a vegetable oil to form nanofluids. The effectiveness of using nanofluids with the respect to dry, flood, and pure minimum quantity lubrication strategies was investigated at different cutting speeds. Results showed that the nanofluid with the lowest size of graphene nanoplatelets promoted the best surface quality assuring a 6% and 15% reduction in surface roughness at the highest and lowest cutting speed, respectively, compared to flood condition that represents the current machining standard. In addition, the use of the graphene nanoplatelets of the lowest size promoted the formation of a 23% thicker severe plastic deformed layer compared to the flood case at the highest cutting speed. These findings prove that the nanoparticles’ efficiency as additives in a metalworking fluid depends on their size, which, in turn, influences their thermo-physical characteristics.