Effect of WC content on the microstructure and mechanical properties of Ti(C,N)-based cermets fabricated by in situ carbothermal reduction of TiO2

Abstract

The effect of WC content on the microstructure and mechanical properties of Ti(C,N)-based cermets fabricated by in situ carbothermal reduction of TiO2 was investigated using XRD, SEM, TEM, and EDX. After sintering, the final microstructure of the cermets prepared via this novel method was mainly characterized by white core/gray rim grains and black core/gray rim grains, and the morphology of the ceramic grains was different from that in traditional cermets. It was found that WC directly participated in the formation of white cores, thus the volume fraction of grains with white cores increased as the content of WC increased, while the volume fraction of the grains with black cores decreased with increasing WC content. Moreover, the interfaces between the binder phase and rims outside the white cores were rough, whereas the interfaces between the binder phase and rims outside the black cores were smooth and an orientation relationship of (200)R//(111‾)B with a perfectly coherent boundary between them. The average grain sizes of the cermets decreased as the content of WC increased, especially when the WC content exceeded 8 wt%. In addition, macropores appeared in the cermets as the WC content exceeded 12 wt%. Overall, the microstructure of the cermets with 8 wt% WC content was the most homogeneous and densest. The transverse rupture strength, hardness and fracture toughness all initially increased and then decreased as the WC content increased.