Performance of PVD (Zr,Ti)N-coated cemented carbide inserts in cutting processes

(Zr,Ti)N coatings with two different gradient structures were deposited on YT15-cemented carbide inserts by multi arc ion plating. Microstructure and properties of these coatings were examined. Dry cutting tests of these coated inserts against 40Cr hardened steel are carried out. This paper presented a detailed analysis of the cutting performance and wear mechanism of these coated inserts. The critical load of EGC shows a little increase compared with TGC because of the thermal expansion coefficient gradient. Compared with YT15 tool, (Zr,Ti)N-coated tools lead to a high quality and good consistency of machined surface during the whole machining process; the cutting temperature will also decrease, but the cutting force change a little. The abrasive wear and boundary wear are the main mode of flank wear, and crater wear and adhesive wear are the main rake wear modes during the machining of 40Cr hardened steel. The (Zr,Ti)N coatings effectively improve the wear resistance of the tools especially the crater wear. The thermal expansion coefficient gradient structure of EGC will reduce the thermal damage of the coating, and its multi-layer structure will mitigate and block the initiation and propagation of microcracks.