Inconel 625 sustainable milling surface integrity and the dependence on alloy processing route

The discovery of deepwater oil and gas sources has altered the scenario of world production of oil products, attracting even more attention to nickel superalloys. However, this class of materials can be used in several applications. Furthermore, nickel superalloys are highly dependent on their processing history, and the manner in which superalloys react to machining can directly affect the finished product. This work aims to evaluate the surface integrity of two different materials after cryogenic side-milling in conditions that stimulate severe plastic deformation (SPD) and high heat generation. The results show that the material response to machining depends strongly on the pre-processing route instead of most assumptions. While cryogenic cooling led to significant sub-surface hardness and microstructural changes in wrought Inconel 625 alloy, such changes were not observed for clad Inconel 625. Therefore, in order to achieve significant surface integrity changes, process parameters need to be selected and optimized accordingly. Also, the findings indicate that some new factors established significant affect/change surface integrity: (a) SPD through a high r_β/h ratio; (b) the specific pre-processing thermomechanical history of the workpiece material; and (c) and cryogenic cooling, by changing material properties, reducing temperature and altering cutting phenomena and chip formation.