Study on the formation of core–rim structure in Ti(CN)-based cermets

Ti(CN)-based cermets were synthesized from Ti(CN)WCMo2CTaCNiCo composite powders by vacuum-low pressure sintering. The phase evolution and the formation of core–rim structure in Ti(CN)-based cermets were systemically investigated during difference reaction stages at 950–1450 °C. The results show that the secondary carbides such as Mo2C and TaC are begun to dissolve at 950 °C, finished at 1150 °C, and the solution temperature of WC phase is range from 1150 to 1300 °C, which are result in increase of the cermets lattice constant. At the same time, the inner rim is also formed, and Ti(CN)-based cermets are composed of (Ti, W, Mo, Ta)(CN) and Ni/Co solid solution phase. While at 1350 °C, it was found that the outer rim began to precipitate from the liquid phase with the metal binder. With increase of sintering temperature, mechanical properties of cermets improved obviously were related intimately to the increase of outer rim thickness.

► At higher temperatures from 1150 to 1300 °C, the lattice constant of cermets increased with the disappearance of WC phase. ► The outer rim began to form a liquid phase with the metal binder at 1350 °C. ► The mechanical properties improved obviously were related to the increase of outer rim thickness from 1400 to 1450 °C.