Densification kinetics of the ultra-fine pure WC powder in graphite dies with different internal diameters is studied using the steady-creep model. The stress exponent n in the early and later soaking periods at temperatures ranging from 1400 to 1500 ℃ is determined by linear fitting. The densification mechanism is revealed to be GB diffusion at n=2 and dislocation climb-controlled creep at n=4.5. The current density increases with the decrease of internal diameter, which leads to the stronger electromigration effect and is responsible for the reduction of Q. The lowest densification activation energy Q under GB diffusion and dislocation climb-controlled creep is obtained to be 171.9 and 514.7 kJ/mol in the graphite die with an internal diameter of 10 mm. However, the contribution of external load on densification has an inverse sequence compared to that of the current density with the increase of internal diameter. As a result, the final relative density of samples sintered in the graphite die with an internal diameter of 25 mm is higher than that in the graphite die with an internal diameter of 20 mm at all the studied sintering temperatures regardless of the reduced Q.

Keywords: Spark plasma sintering, Tungsten carbide, Densification kinetics.