WEAR OF CERMET CUTTING TOOLS COATED WITH PHYSICALLY VAPOR-DEPOSITED TIN

Physically vapour deposition coated cutting tools presently take a lar ge share of the cutting tool market. Recently, coated TiC-based cermet s also appeared on the market, exhibiting cutting behaviour which make s them competitive with coated WC-based hardmetals. The present paper discusses the results of a study devoted to the wear mechanisms of TiN (physically vapour deposited) coated TiC-based cermets. Static diffus ion experiments were conducted in order to simulate the diffusion proc ess across the tool-workpiece interface at high temperature and pressu re. Additionally, experimental uncoated and TiN-coated cermets were te sted in machining steel, and the depth profiles of the worn edges were analysed. The diffusion couples and the worn cutting tools were analy sed by scanning electron microscopy, energy-dispersive spectroscopy an d Auger electron spectroscopy in order to identify the dominant wear m echanisms. The results of cutting tests with the experimental inserts confirmed the beneficial effect of TiN coating on the tool life of cer met cutting tools. At high cutting speeds the wear of uncoated and coa ted cermet tools is mainly determined by diffusion across the tool-wor kpiece interface. A TiN coating containing a high concentration of str uctural defects can only partially hinder diffusion. The association o f defects enables the diffusion of carbon and nitrogen as well as meta l atoms through the apparently dense TiN layer. However, outward nitro gen diffusion may prevent carbide grain decomposition, resulting in ex tended tool life.