Advances in modern nitrogen-containing hardmetals and cermets

Properties and performances of modern hardmetals and cermets can be significantly improved by introducing nitrogen (N) to optimise micro- and macro-structures. However, nitridation and de-nitridation complicate metallurgical reactions during sintering. By using SEM/EDS, XRD, DSC, DTA, mass spectrometer (MS) and dilatometer (DL), phase reactions, phase equilibria, melting points and sintering behaviours of WC–TiC–TiN–, WC–TiC–TiN–Co– and WC–TiCN–TaC/NbC–Co/Ni– alloys have been studied. Based on better understanding of the above systems related to sintering atmospheres, various new cutting tool materials with specially designed chemistries, micro- and macro-structures and properties have been prepared. The new materials can be classified as (1) cubic phase-free-layered surface (CFL) materials for substrates of coating tools; (2) graded materials with hard cermet surface and tough hardmetal core; (3) complex multi-laminated materials with graded compositions within each surface layer; and (4) TiN-based self-lubricated materials. The keys to obtain desired materials are to control metallurgical reactions during sintering and to design chemical compositions of the materials properly.