Effect of carbon content on the microstructure and mechanical properties of (Ti, W, Ta, Mo)(C, N)-(Co, Ni) cermets

Five model alloys with different carbon content were studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in combination with energy dispersive X-ray analysis (EDX). Vickers hardness (HV) and transverse rupture strength (TRS) were measured, and continuous turning tests were performed. The aim of this work was to relate the variation in carbon content to the resulting microstructures and to the mechanical behaviour of these model alloys. An increased carbon content resulted in decreased concentrations of tungsten and titanium in the binder phase, a lower volume fraction of undissolved Ti(C, N) cores, and a higher volume fraction of heavy (Ti, W, Ta)(C, N) cores. The volume fractions and compositions of the other phases were not much affected by the carbon content. In addition, a coarser carbonitride grain structure was observed in the material with a high carbon content. Hardness was found to decrease and TRS to increase with carbon content, but no obvious trend was found for the wear resistance as a function of carbon content. Several microstructural features interact and influence the final properties. The heavy (Ti, W, Ta)(C, N) cores formed during sintering and a highly solution hardened binder phase seem to be favourable for a high wear resistance. (C) 1999 Elsevier Science Ltd. All rights reserved.