Comparison of the thermal shock resistance of WC based cemented carbides with Co and Co-Ni-Cr based binders

Abstract

The damage induced by thermal shock in WC-43vol%Co and WC-40.7vol%Co-Ni-Cr cemented carbide grades has been analyzed by measuring the loss of fracture strength after repeated water quenching experiments from temperatures ranging from 400°C to 700°C. At 500°C and lower temperatures, damage is more severe for the WC-Co-Ni-Cr alloy, this being associated to its lower toughness compared to that of the WC-Co grade. However, the opposite is found when the temperature step used in quenching experiments reaches 700°C. In this case, the relative loss of strength is much higher for the WC-Co material. Microstructural analyses confirm that this phenomenon is likely associated to the precipitation of very fine W-rich intermetallics in the binder phase of this alloy, which are not observed in the WC-Co-Ni-Cr grade. Toughness is critical since thermal shock damage is characterized by the formation of microcracks at distances ranging from 10 to 20μm from the sample surface. These cracks are preferentially located at the WC-metal interfaces. Results obtained from cylindrical samples allow to separate microstructural damage from that induced by stress concentrators present in the prismatic ones.