Study of the effect of the electric current density on the densification kinetics of the ultra-fine pure WC powder during spark plasma sintering
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Densification kinetics of the ultra-fine pure WC powder in graphite dies with different internal diameters is studied usingthe steady-creep model. The stress exponent n in the early and later soaking periods at temperatures ranging from 1400 to1500 ℃ is determined by linear fitting. The densification mechanism is revealed to be GB diffusion at n=2 and dislocationclimb-controlled creep at n=4.5. The current density increases with the decrease of internal diameter, which leads to thestronger electromigration effect and is responsible for the reduction of Q. The lowest densification activation energy Q underGB diffusion and dislocation climb-controlled creep is obtained to be 171.9 and 514.7 kJ/mol in the graphite die with aninternal diameter of 10 mm. However, the contribution of external load on densification has an inverse sequence comparedto that of the current density with the increase of internal diameter. As a result, the final relative density of samples sinteredin the graphite die with an internal diameter of 25 mm is higher than that in the graphite die with an internal diameter of20 mm at all the studied sintering temperatures regardless of the reduced Q.
Abstract
Densification kinetics of the ultra-fine pure WC powder in graphite dies with different internal diameters is studied usingthe steady-creep model. The stress exponent n in the early and later soaking periods at temperatures ranging from 1400 to1500 ℃ is determined by linear fitting. The densification mechanism is revealed to be GB diffusion at n=2 and dislocationclimb-controlled creep at n=4.5. The current density increases with the decrease of internal diameter, which leads to thestronger electromigration effect and is responsible for the reduction of Q. The lowest densification activation energy Q underGB diffusion and dislocation climb-controlled creep is obtained to be 171.9 and 514.7 kJ/mol in the graphite die with aninternal diameter of 10 mm. However, the contribution of external load on densification has an inverse sequence comparedto that of the current density with the increase of internal diameter. As a result, the final relative density of samples sinteredin the graphite die with an internal diameter of 25 mm is higher than that in the graphite die with an internal diameter of20 mm at all the studied sintering temperatures regardless of the reduced Q.
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