Effect of carbon content on the microstructure and mechanical properties of Ti(C, N)-based cermets

Three series of Ti(C, N)-based cermets with various carbon content were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). Hardness (HV) and transverse rupture strength (TRS) were also measured. A lower carbon content resulted in the aggregation of ceramic grains because the absorbed oxygen of the powder mixture could not be outgassed completely, and then the ceramic grains could not be well-wetted by liquid metal during sintering. On the contrary, too high carbon content resulted in the formation of graphite phase. An increased carbon content decreased the dissolution of tungsten, titanium and molybdenum in the binder phase. The volume fraction of the binder is not much influenced by the carbon content. The highest hardness and TRS were found for the cermet with 1.5 wt.% carbon addition, which was characterized by fine grains and moderate thickness of rim phase.