During the reactive sintering of W-6%Co-C powder mixtures at 1,500°C under pressure,
the reaction product between these elements depends on the relative contents of carbon
and cobalt. With a carbon content of 7% by mass, the WC monocarbide forms alone
and densification occurs in the presence of a cobalt-based liquid phase. With lower
carbon contents, the hemicarbide W2C forms first and reacts with cobalt to form the
mixed carbide Co3W9C4. The hardness is increased, but the amount of liquid phase is
reduced and the sintering densification is limited. In the presence of the mixed
carbide, the cobalt content should be sufficient to be able to produce the amount of
liquid phase required for sintering densification. For carbon contents greater than 7%,
one obtains the formation of the WC carbide, densified by the cobalt binder, and the
precipitation of free graphite. The choice of the initial carbon content allows thus
to influence the type of phases obtained and the conditions of liquid phase sintering
densification.