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 both a cathodic-arc and an ion-plating technique on a commercial cermet insert are first characterised in terms of adhesion to substrate. Wear 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 by alumina-based particles. The study is addressed to contribute to an understanding of erosion wear mechanisms that are not yet fully assessed, and of reasons why scarce improvements are obtained in interrupted cutting processes by use of coated cermet inserts. It is found that the anti-erosion resistance reflects the coating adhesion to the substrate evaluated by means of scratch tests. These two characteristics, which are mainly influenced by the coating microhardness and thickness, cannot be directly correlated to the anti-wear behaviour obtained in milling trials. This behaviour is likely to be controlled by wearing mechanisms which arise during the interrupted cutting process, mainly due to complex interactions acting at the workpiece-insert interface. When the workpiece material is a steel and the insert substrate is a cermet, an optimisation of the cutting process is not sensibly influenced by use of coatings tested so far. (C) 1997 Elsevier Science S.A.