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 order to describe the deformation mechanisms involved during their use in cutting tool applications. Several compositions were considered all with 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 been performed using scanning electron microscopy and transmission electron microscopy (TEM), complemented by energy dispersive X-ray spectrometry analysis. The results show a strong influence of the Mo content on the ultimate microstructure. The high temperature mechanical behaviour was characterized by three point bending tests in the 900-1200 degrees C temperature range under vacuum, both at constant strain rate and 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 initial Mo content was also observed. These results indicate that the creep behaviour of these Ti(C,N) cermets is strongly related to the deformation micromechanisms of the carbide-carbonitride phase. TEM observations performed on microstructures which had been previously deformed at high temperatures are in good agreement with this hypothesis.