A Study on Microstructure Evolution and Mechanical Properties of Inconel 690 Subjected to Milling Process

The metallic materials subjected to machining‐induced severe plastic deformation can experience alterations of microstructures and mechanical properties, affecting the functional performances of the components. This study concentrates on the microstructure evolution and mechanical properties analysis of Ni‐based superalloy Inconel 690 under severe plastic deformation induced by milling process. The obtained results show that the microstructures of the machined surface and subsurface exhibit the characteristic of gradient distribution. Plastic behaviors involving dislocation multiplication, grain deformation and refinement, increment of local misorientation and average intragranular misorientation, and transition from high‐angle grain boundaries to low‐angle grain boundaries occur in the superficial layer of the machined workpiece. Both the intensity and the affected depth of plastic deformation for the superficial layer are strengthened following the cutting speed and feed increase, which is attributed to higher cutting forces. No white layer and phase transformation is found under all cutting conditions. In addition, the nanohardness of the superficial layer shows the reduction tendency of hardening effect from the surface to the bulk of the machined workpiece material. With the increase in cutting speed and feed, the affected zones of residual stresses and work hardening below the machined surface become wider.