MICROSTRUCTURE AND HIGH-TEMPERATURE MECHANICAL-PROPERTIES OF TIC0.7N0.3-MO2C-NI CERMETS

In this study, the microstructure and the high temperature mechanical behaviour of TiC0.7N0.3-Mo2C-Ni cermets have been investigated in orde r to describe the deformation mechanisms involved during their use in cutting tool applications. Several compositions were considered all wi th a nickel content of 10 wt.%, and with a Mo2C content equal to 5, 10 or 20 wt.%. A microstructural characterization of these cermets has b een performed using scanning electron microscopy and transmission elec tron microscopy (TEM), complemented by energy dispersive X-ray spectro metry analysis. The results show a strong influence of the Mo content on the ultimate microstructure. The high temperature mechanical behavi our was characterized by three point bending tests in the 900-1200 deg rees C temperature range under vacuum, both at constant strain rate an d at constant load (creep conditions). Similar high temperature tests were performed on samples in which the metallic binder was chemically removed (hard-phase skeleton). The same dependence between the steady state creep rate and the temperature was found for the cermets and for their associated hard-phase skeleton. A significant effect of the ini tial Mo content was also observed. These results indicate that the cre ep behaviour of these Ti(C,N) cermets is strongly related to the defor mation micromechanisms of the carbide-carbonitride phase. TEM observat ions performed on microstructures which had been previously deformed a t high temperatures are in good agreement with this hypothesis.