Wear mechanisms of PVD-coated PCBN cutting tools

The wear characteristics of PVD coated (TiN, TiSiN, TiAlN, and AlCrN) polycrystalline cubic boron nitride (PCBN) cutting tools were compared to those of uncoated PCBN during single point turning of case hardened steel 16MnCr5. Post-cutting observations of the worn inserts were performed using high resolution field emission gun scanning electron microscope (FEG-SEM) in combination with focus ion beam (FIB) and analytical transmission electron microscopy (TEM). Substantial differences in the wear behaviour of the different coating materials could therefore be observed. In particular, a remarkable tendency for TiN to exhibit plastic deformation was revealed while TiSiN exhibited a more brittle behaviour evidenced by adhesive wear and microchipping. TiAlN and AlCrN on the other hand exhibited less workpiece adhesion. The wear mechanisms of the above thin coating layers are discussed and interpreted in light of thermal, mechanical, and frictional conditions occurring at the tool-chip contact.