Surface integrity in high-feed roughing of Inconel 718 with SiAlON end mills

Conventional machining processes for hard-to-machine nickel-based alloys involve carbide tools, which exhibit low productivity at high tool wear rates. Novel tool concepts such as SiAlON-ceramic high-feed end milling tools show great potential to reduce the time required for the roughing process. However, these cutting processes feature high cutting speeds while avoiding cutting fluids, which leads to high thermomechanical loads. Since an unaffected rim zone must be ensured, this paper investigates the surface integrity effects on Inconel 718 machined with SiAlON-ceramic end mills. Particularly, the cutting forces, surface temperature, microhardness and microstructural damages in the cross-section are evaluated. In the selected slot milling operation, surface temperatures of up to 1,250 °C were measured and plastic deformations could be identified up to a depth of 35.5 μm in the bottom of the slot. The side walls are affected up to a depth of 69.6 μm from the surface. Microhardness measurements of the bottom of the slot show a hardening of the machined surface of 17.9 %, which does not reach deeper than 150 μm into the basic structure.