Wear mechanisms of multilayer coated cemented carbide cutting tools

Turning experiments were performed with cemented WC-Co cutting tools coated with two-layer and three-layer overcoats of TiC/Al2O3 and TiC/Al2O3/TiN, respectively. For comparison, uncoated NC-Co tools were also tested under similar cutting conditions. The predominant wear mechanisms of the various ceramic overcoats and cemented WC-Co were investigated using surface profilometry, scanning electron microscopy, and energy dispersive X-ray analysis. Representative results of the tool wear behavior are presented, and the significance of each ceramic layer on the overall tool wear resistance is interpreted in light of the identified dominant wear mechanisms. Delamination wear characterized by the propagation and linkage of surface, subsurface, and interfacial cracks, abrasion, surface plastic shearing, plucking of carbide grains and dissolution/diffusion are shown to occur depending on the tool material. These wear processes are not mutually exclusive; they may occur simultaneously at different positions on the same tool surface. Based on nose wear data, correlations between wear lives of coated and uncoated tools and feedrate are established.