High speed turning of Inconel 718 using PVD-coated PCBN tools

Five different coatings and two PCBN grades were evaluated when high speed turning Inconel 718. Tool life was 40% higher when employing TiSiN coated over uncoated inserts at 200 m/min. When operating at 300-450 m/min however, coatings provided no appreciable benefit. Workpiece surface roughness varied between ∼0.25 and 1.05 μm Ra while cutting forces were <300 N. Increased workpiece microhardness and microstructural deformation were apparent with worn inserts. Medium cBN content (65%) inserts generated near surface compressive residual stresses of approximately −440 MPa as opposed to values of −90 MPa (measured parallel to feed) when using low cBN content (50%) tools.