T1(C,N) CERMETS - METALLURGY AND PROPERTIES

An overview of the metallurgical reactions during the vacuum sintering process of powder mixtures for the manufacture of cermets is presented. The relatively complex phase reactions in the multi-component system Ti/Mo/W/Ta/Nb/C,N-Co/Ni are discussed. The liquid binder phase reacts with titanium carbonitride by preferentially dissolving titanium carbide leaving titanium nitride undissolved. The compositions and the amounts of the gas species set free during the sintering process were monitored and led - together with differential thermal analysis - to a better understanding of the mechanisms that govern the sintering behaviour. The properties and the microstructure of cermets depend on the nature and the alloy status of the prematerials. The composition of the prematerials with respect to the carbon-nitrogen ratio, the stoichiometry of the hard phase and the amount and composition of the binder phase have a decisive influence on the properties and the cutting performances of the final products. Optimization of the properties with respect to the desired performance is possible. Examples of the cermet cutting performance in various applications are discussed.