Machining-induced microstructure of Inconel 718 in cryogenic environment

This paper investigates the effect of cryogenic cooling on surface integrity of Inconel 718 in milling operations. The cutting process was conducted using carbide coated ball nose milling inserts and liquid nitrogen as the coolant. A full factorial with three factors two levels each was adopted to run the experiments. Results revealed that the surface roughness were in the range of 0.134 μm to 0.264 μm which were less than the values obtained using manual polishing process (≈0.5 μm). The roughness was significantly affected by the interaction between cutting speed and feed rate followed by the radial depth of cut. Microstructure beneath the machined surface exhibited some plastic deformation down to 30.93 μm due to the sliding of tool over the surface during the shearing process that increased the cutting pressure at elevated temperature and caused deformation of the grain structure, which was better than dry machining.