Effects of metal phases and carbides on the microstructure and mechanical properties of Ti(C,N)-based cermets cutting tool materials

A study to enhance the mechanical properties of Ti(C0.7,N0.3)-based cermets cutting tool materials by adding different contents (weight percentage, wt%) of Ni-Co (the ratio of Ni to (Ni+Co) was 0.4), Mo, WC, TaC and HfC was presented. The phase composition, element distribution, crack propagation and the effects of the five additives on the mechanical properties and microstructure of Ti(C,N)-based cermets were investigated, and the relationships between the mechanical properties and microstructure were discussed. The results indicated that there were three types of core-rim structures, and they were black core-white rim, black core-grey rim and white core-grey rim, respectively. The grain size of Ti(C,N) in the microstructure reduced with an increase in the content of Ni-Co, and the volume fraction of continuum (Ti,W,Mo) (C,N)-Ni-Co increased with an increase in the contents of Ni-Co and Mo. The white phase (Ti,W) (C,N) almost did not exist and the volume fraction of continuum (Ti,W,Ta,Mo) (C,N)-Ni-Co increased with a reduction in the content of WC and an increase in the content of TaC, which due to the better solubility of TaC in the binder phase. However, the additive HfC did not form solid solution with the other carbides and agglomerated because of its poor affinity with other carbides, poor solubility in binder phase Co and good affinity with oxygen. More than 4.0 wt% of Mo was not helpful to the improving of the mechanical properties of Ti(C,N)-based cermets. The additive TaC enhanced the flexural strength and the additive HfC enhanced the hardness of Ti(C,N)-based cermets. The results demonstrated that Ti(C,N)-based cermets TWM4NC8, TWMNCT6 and TWMNCTH1 exhibited excellent mechanical properties.