Novel Route for Preparing Diamond-Enhanced Cemented Carbides via Reactive Sintering

Abstract

Hardmetals are cemented carbides consisting of the hard ceramic phase WC and the ductile metallic binder Co. They offer an outstanding combination of hardness and fracture toughness. Hence, they have a widespread use across the manufacturing industry. However, due to the increasing requirements for tool material, the combination of the beneficial properties of hardmetal and diamond is a long sought-after objective. In this work, a new approach was evaluated to reduce the formation of graphite due to the phase transformation of diamond during the sintering of compounds together with hardmetal. Earlier trials could not fully suppress the phase transformation despite using alternative Ni-instead of conventional Co-based binder systems and field-assisted sintering (FAST) to reduce required sintering temperatures and time. To lower the amount of graphite formed during sintering even further, a reactive sintering process was developed. The increased sinter activity due to the in situ synthesis of WC has the potential to decrease the needed temperature to achieve a pore-free compact. For the first time, a WC-Ni hardmetal produced from elemental powders was successfully used as a matrix in a diamond-enhanced cemented carbide (DECC). Different approaches regarding carbon sources and the extent of reactive material were pursued. The introduction of a carbon deficit by adding metallic W to a mixture of WC and Ni, which is essentially partial reactive sintering, leads to an increased relative density compared to the reference of 97.3%.