Effect of carbon content on the microstructure and mechanical properties of ultra-fine grade (Ti,W) (C,N)-Co cermets

Effect of carbon addition on the microstructure and mechanical properties of TiC(sub) –TiN(nm)–WC–Co–C system cermets was studied in this work. The microstructure was investigated by means of X-ray diffractometry (XRD), scanning electron microscope (SEM) in combination with energy dispersive spectrometer (EDS). Mechanical properties such as transverse rupture strength (TRS), fracture toughness and hardness were also measured. Results show that the ceramics in cermets are composed of black core/grey rim and white core/grey rim grains, and of which most cores are of black color. The amount of white core/grey rim structure and the carbonitride grain size increase and the volume fraction of undissolved Ti(C,N) cores decreases with the increase of carbon content. Results also show that the transverse rupture strength (TRS) as well as the hardness exhibits a similar trend, i.e. first increases with the increase of carbon content, reaches the first peak value, then decreases with further increase of carbon content, reaches the lowest value at 1.5 wt% C, subsequently reaches the highest value at 2.0 wt% C, and decreases again with further increase of carbon content, while the fracture toughness of the cermets does not increase monotonously with the increase of carbon content.