PHYSICALLY VAPOR-DEPOSITED COATINGS ON CERMETS - PERFORMANCE AND WEAR PHENOMENA IN INTERRUPTED CUTTING

Cermets are titanium based cutting materials with high resistance against abrasive and chemical wear. Nevertheless, chemical reactions take place between the binder materials and steel. Recent developments of substrates and the use of physically vapor deposited coatings focus on further improvement of the wear and fracture resistance of cermets in order to enlarge the held of application towards tempered and austenitic steels and towards more rigorous interrupted cutting operations. Binary and ternary titanium based hard coatings deposited onto different cermet substrates by physical vapor deposition (PVD) processes were examined in interrupted cutting of tempered, case hardening and austenitic steels. PVD (Ti,Zr)N and Ti(C,N) coatings improve tool life in the machining of tempered steel. The shape of the tool life curves is linked to the strength of the work material as a function of temperature. The PVD TiN coating reduces flank wear of the tools but does not increase the resistance against chipping and breakage in machining of case hardening steel. The thermal conductivity of the cermets is of great importance for performance in interrupted cutting. Severe and early decoating of the tools occurred in machining of austenitic steel owing to adhesive and cohesive coating failure.