Solid-state solubilities of grain -growth inhibitors in WC-Co and WC-MC-Co hardmetals

The solubilities of the most common grain -growth inhibitors (GGIs) Cr, V, Ta, Mo, Nb, Zr and certain combinations there of in the binder phase of WC-Co hardmetals as well as hardmetals of the type WCTiC-TiN-TaC-NbC-Co containing an fcc MC carbide (or carbonitride) phase MC(WC-MC-Co hardmetals) were analysed by means of WDS-EPMA. The carbon potential of the binder phase was fixed at its highest and lowest maxima by the presence of either graphite or eta (M6C) phases. In case of low-carbon hardmetals the composition of M6C, and in the MC-containing hardmetals the composition of the MC phase, was analysed. Two types of solubilities were determined. The first type was measured after controlled cool-down from liquid-phase sintering temperature and represented the binder phase state of an industrially prepared hardmetal. The second type representing the equilibrium solubility was measured in alloys annealed at 1000 degrees C for 168 h after liquid -phase sintering. The measured solubilities were subsequently used to prepare hardmetals with an optimised GGI concentration. The samples were analysed with respect to hardness, toughness, magnetic properties, transverse rupture strength and Weibull parameter. A complex doping with Cr, V and Ta with optimised concentrations near the solubility limit of these metals in the binder phase turned out to yield best combination of mechanical properties and reliability. This was successfully adopted in industrial production. (C) 2016 Elsevier B.V. All rights reserved.