Hardmetals with Ru-containing multi-element binders: Composition, constitution and phase formation

In spite of the rather high cost of Ru, CoRu binders are commonly used by the industry for the production of cemented carbides with performance demands at high temperatures. In a recent study it was shown that the solubility of W in Co-binders is considerably increased by the addition of Ru (both at low and at high carbon contents), which can significantly affect aspects such as grain growth inhibition, hardness, corrosion resistance and high temperature strength. The present work has extended the study to further binder chemistries: Co, Ni, CoNi and CoNiCr, which have been evaluated both with and without Ru additions. The results indicate that Ru additions increase the solubility of elements like W and Cr for all binder chemistries, both at low and at high carbon contents. The solubility of W is the lowest in the Cr-containing systems (CoNiCr and CoNiCrRu), however, due to the presence of Cr, the total amount of elements in solution is the highest from all binders. The results clearly demonstrate that the WC growth behaviour is significantly affected by the chemistry of the binder system, i.e. the chemical environment of the growing WC grains, which is strongly linked with the chemical activity of carbon in the system.