Mechanical properties of machined surface for high-speed machining Inconel 718 considering microstructural evolution

The altered microstructure of the machined surface during high-speed machining (HSM) Inconel 718 significantly modifies its mechanical properties. This study focuses on the residual stress and hardness of the machined surface, considering the microstructural evolution. The microstructure characteristics was measured using electron backscatter diffraction and precession electron diffraction techniques. A hardness prediction model that considers the grain size and geometrically necessary dislocation (GND) density was developed and verified. The contributions of different microstructural characteristics and cutting parameters to the hardness were analyzed. The influences of the cutting parameters and dynamic recrystallization (DRX) behavior on the residual stress were studied by experiments and simulations. The results indicated that the developed model can accurately predict the hardness of a machined surface when nanoscale grains are generated. The hardness caused by the grain size was dominant at approximately 72 %. With an increase in the cutting speed, the hardness first increased and then decreased, which was consistent with the changing trend of the low-angle grain boundaries and GND density of the machined surface. Owing to the DRX behavior, the surface residual stress, maximum compressive residual stress, depth of the maximum compressive residual stress, and depth of the residual stress influence layer in the cutting speed direction changed by 11.89 %, 17.46 %, 9.97 %, and 7.41 %, respectively, and the data perpendicular to the cutting speed direction were 12.80 %, 14 %, 11.68 %, and 7.87 %, respectively. These results indicated that a material with excellent mechanical properties can be obtained by controlling microstructural evolution in HSM.