A TRIBOLOGICAL EVALUATION OF COATED CERMET SYSTEMS FOR CUTTING TOOLS

An experimental study of coated cermet systems used for cutting tools in milling rests and for target materials in erosion tests is focused on two PVD techniques. TiN and TiN + TiCN coatings deposited each by b oth a cathodic-arc and an ion-plating technique on a commercial cermet insert are first characterised in terms of adhesion to substrate. Wea r degradation phenomena occurring on the substrate and coated systems are studied in terms of flank wear observed during dry face milling of AISI-SAE 1045 and crater damage observed during oblique impingement b y alumina-based particles. The study is addressed to contribute to an understanding of erosion wear mechanisms that are not yet fully assess ed, and of reasons why scarce improvements are obtained in interrupted cutting processes by use of coated cermet inserts. It is found that t he anti-erosion resistance reflects the coating adhesion to the substr ate evaluated by means of scratch tests. These two characteristics, wh ich are mainly influenced by the coating microhardness and thickness, cannot be directly correlated to the anti-wear behaviour obtained in m illing trials. This behaviour is likely to be controlled by wearing me chanisms which arise during the interrupted cutting process, mainly du e to complex interactions acting at the workpiece-insert interface. Wh en the workpiece material is a steel and the insert substrate is a cer met, an optimisation of the cutting process is not sensibly influenced by use of coatings tested so far. (C) 1997 Elsevier Science S.A.