Tool life and surface integrity when machining Inconel 718 with PVD- and CVD-coated tools

Test results show that when machining nickel-based Inconel 718 alloy under the cutting conditions investigated, the multilayer PVD-coated carbide grades gave the best performance in terms of tool life. This was due to their higher hardness, tough ness, abrasion resistance, good heat transmission behavior of the multiple (TiN/TiCN/TiN) coatings as well as thicker coating layer (relative to the single-coated grade). The smaller grain size and higher density of their substrates also enhance the strength and hardness of the multi-coated PVD tools, thus providing higher resistance to attrition wear. Machining with the single-PVD TiN-coated grade generally produced a better surface finish due to the polishing action of the honed cutting edge and the generation of a uniform finishing edge with coating bottom on the trailing edge during machining. The absence of any significant tearing on the machined surfaces after cutting with the PVD- and CVD-coated tools at the cutting conditions investigated can be attributed to the low friction coefficient of the coating materials. Excessive plastic deformation, however occurred on the machined surfaces. Increased hardness of the machined surface layer (up to 0.6 mm deep) also occurred as a result of high pressure and temperature generated during the machining operation. This tends to increase the hardening rate of Inconel 718.