Experimental study of invariant equilibria in the Co-W-C and Co-W-C-Me (Me= Ti, Ta, Nb) systems

New experimental information on liquid/solid invariant equilibria in system s of importance for cemented carbides has been generated using a differenti al thermal analysis (DTA) technique. The temperatures of the invariant equi libria liq + fcc-Co + WC + graphite and liq + fec-Co + WC + M6C have been d etermined for the Co-W-C system. For the Co-W-C-Me systems, where Me is a c ubic carbide forming metal (Ti, Th, or Nb), the corresponding temperatures of the invariant equilibra, including the cubic carbide phase, have been me asured. The compositions of the M6C phase and the cubic carbide after rapid cooling from 1400 degreesC have been determined by electron probe microana lysis. The M6C phase was found to accept Ta or Nb on its W position, wherea s the acceptance of Ti was negligible. The measured solubility of W in Ti-b ased cubic carbide was in good agreement with previous determinations. Howe ver, the W solubility was found to be considerably lower for Ta- and Nb-bas ed cubic carbide compared to data reported in the literature.