MICROSTRUCTURAL DEVELOPMENT DURING THE LIQUID-PHASE SINTERING OF CEMENTED CARBIDES

Abstract

Measurements have been made of the contiguity, the dihedral angle, and the continuity of the carbide phase in alloys of a number of transition-metal carbides with cobalt, which were prepared by liquid-phase sintering. During sintering, the carbide contiguity in a given alloy develops towards an equilibrium value, which is directly related to the dihedral angle between carbide grains and therefore to the relative values of the interfacial energy and the contiguous boundary energy. A direct relationship between the contiguity and the angle of contact of the liquid on the carbide, however, does not exist. The contiguity at the start of sintering depends to some extent on the history of the specimen before liquid-phase sintering and in most cases is higher than the equilibrium value. Observations were made which indicate that the carbide grains in the majority of cemented carbides exist as a continuous skeleton. Arguments are presented to show that neither the presence of such a skeleton nor the presence of contiguity need be entirely inconsistent with accepted theories of densification.