Evaluation of milling parameters on the surface integrity of welded inconel 625

Nickel-based alloys are used widely in aerospace components and the oil and gas industry, operating in an extremely adverse environment. These alloys are characterized as difficult-to-machine materials due to their high hardening rate, low thermal conductivity, and superior hot hardness. Since the material and its machining are very expensive, it is important to evaluate how the machining processes deteriorate the surface integrity to prolong the service life of the Inconel components as long as possible. In order to reach this goal, the influence of tool geometry, feed rate, and cutting speed on surface integrity was evaluated for the milling process of Inconel 625 cladding. Qualitative and quantitative mechanical and metallurgical analyses on the surface and subsurface were performed using 3D optical microscopy, scanning electron microscopy (SEM), instrumented indentation, X-ray diffraction for residual stress measurements, and corrosion tests. The results indicate that cutting speed has the greatest influence on specific cutting pressure. The cutting speed and feed rate were the main factors that affected the thickness of the deformed layer. The results suggest that surface and subsurface alterations after machining are driven by mechanical-thermal loadings and cause beneficial results related to corrosion resistance and compressive residual stress.