Surface Integrity Analysis of Inconel 718 after Turning with Different Solid Lubricants Dispersed in Neat Oil Delivered by MQL

Nickel-based superalloys have been widely employed in the aerospace industry because of their high mechanical strength that is maintained even at elevated temperatures. However, because of their outstanding properties they are considered difficult-to-machine material. Thus, any attempt to improve machining productivity of such material is encouraged. Since they are used in components with great technical responsibility, microstructure and residual stress changes caused by machining should be monitored. This paper presents a study of the surface integrity (roughness, microstructure, microhardness and residual stress) in turning of Inconel 718 with solid lubricants (graphite and molybdenum disulfide - MoS2) dispersed in oil that were delivered in the cutting zone by the MQL technique. Addition of graphite in the oil improved the tool life but the same did not occur with MoS2. No significant microstructural changes were observed on the machined surfaces with the addition of solid lubricants. Negligible influence of them in surface roughness and residual stresses was noticed after machining Inconel 718 under different cutting conditions.