Effect of WO3 content on microstructure and mechanical properties of dual-grain structured hardmetals fabricated by in-situ carbothermal reduction of WO3

In this study, the effects of WO3 content on the microstructure of dual-grain structured hardmetals prepared through in-situ carbothermal reduction of WO3 were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Moreover, mechanical properties of hardmetals with different WO3 content were measured by mechanical property testing devices. Results showed that fine WC grains were formed through in-situ reaction between WO3 and carbon black, and the hardmetals mixed with WO3 exhibited obvious bimodal distribution. As the WO3 content increased, the average WC grain size first decreased and then increased, however, the trend of density change was opposite. Overall, microstructures of hardmetals with a WO3 content of 30 wt% were most homogeneous and dense. Moreover, in hardmetal with a WO3 content of 30 wt%, a low-angle grain boundary at the WC/WC interface was observed. In addition, a perfectly coherent state was observed at the interface between binder phase and fine WC grain formed via in-situ reaction of WO3 and carbon. Both hardness and transverse rupture strength (TRS) first increased and subsequently decreased, while fracture toughness (K-IC) initially decreased slightly and then decreased considerably. The dual-grain structured hardmetal with 30 wt% WO3 could achieve a combination of high hardness, TRS and K-IC.