Enhanced densification of liquid-phase-sintered WC-Co by use of coarse WC powder: Experimental support for the pore-filling theory

Abstract

Densification during liquid-phase sintering of WC-Co with various WC powder sizes has been measured in order to identify the densification mechanism. During heating of powder compacts in the solid state, densification was enhanced with a reduction of WC powder size. However, the behavior was reversed when the densification occurred in the presence of a liquid: enhanced densification with increasing WC powder size. This result is in contradiction to a prediction of the conventional theory of liquid-phase sintering, the contact flattening theory, but in good agreement with a prediction of the pore-filting theory. Microstructural analysis further confirmed that the densification at the liquid-phase sintering temperature occurred by pore filling. The calculated densification kinetics based on the pore-filling theory also fitted well with the measured data. The observed densification behavior thus demonstrates experimentally the prediction of the pore-filling theory that the densification is enhanced with increasing average grain size for the same pore size distribution.