On the constitution and cobalt alloy formation in WC-1.4 wt% Ru-9.5 wt% Co cemented carbides

Abstract

Our work confirms that the addition of Ru to Co-based cemented carbides significantly broadens the carbon processing window. Using a WC-10.9 wt% (Co-12.8Ru) alloy, the width of the two-phase window is extended from about 0.16 wt% C (Ru-free) to about 0.21 wt% C on addition of Ru. According to semi-quantitative EDS analysis, the amount of W dissolved in the Co binder is significantly higher in Ru-containing materials at all carbon contents. This higher degree of solubility is also reflected in the lattice parameter. When decreasing the carbon content (from precipitation of graphite to the formation of eta carbides), the lattice parameter increases steadily from 3.585 Å to 3.609 Å respectively. In contrast, Ru-free materials present 3.548 Å in equilibrium with graphite, and 3.576 Å in equilibrium with eta carbides. The relative magnetic saturation value of the alloys with Ru was significantly lower when compared to Ru-free alloys (from 80.2% at graphite precipitations to 41.4% with dendritic eta phase), which is also in agreement with the higher W solubility observed in these alloys. DTA measurements of WC-4.4 wt% Ru-30 wt% Co samples (same Ru to Co ratio in the nominal composition) demonstrated a similar melting and solidification regime as compared to Ru-free WC-30 wt% Co materials.