EHTT2022-Tribological Mechanism of Graphene/Ionic Liquid Nanofluid on Grain/Workpiece Grinding Interface under Nanofluid Minimum Quantity Lubrication

Abstract Graphene nanosheets and ionic liquids (ILs) both have excellent heat transfer and lubricating properties and both have great potential in minimum quantity lubrication (MQL) grinding, however the grinding performance of graphene/IL nanofluids under nanofluid minimum quantity lubrication (NMQL) is still unclear. This research firstly evaluates the grinding performances of graphene/IL nanofluids under NMQL experimentally. The evaluation shows that graphene/IL nanofluids can further strengthen both the cooling and lubricating performances compared with MQL grinding using ILs only. The specific grinding energy and grinding force ratio can be reduced by over 40 percent at grinding depth of 10 μm. Workpiece machined surface roughness can be decreased by over 10 percent, and grinding temperature can be lowered over 50 ℃ at grinding depth of 30 μm. Aiming at the unclear tribological mechanism of graphene/IL nanofluids, molecular dynamics simulations for abrasive grain/workpiece grinding interface are performed to explore the formation mechanism of physical adsorption film. The simulations show that the grinding interface is in a boundary lubrication state. IL molecules absorb in groove-like fractures on grain wear flat face to form boundary lubrication film, and graphene nanosheets can enter into the grinding interface to further decrease the contact area between abrasive grain and workpiece. The interlayer shear effect and low interlayer shear strength of graphene nanosheets are the principal causes of enhanced lubricating performance on the grinding interface. EDS and XPS analyses are further carried out to explore the formation mechanism of chemical reaction film. The analyses show that IL base fluid happens chemical reactions with workpiece material, producing FeF2, CrF3, and BN. The fresh machined surface of workpiece is oxidized by air, producing NiO, Cr2O3 and Fe2O3. The chemical reaction film is constituted by fluorides, nitrides and oxides together.