Effects of AGG on fracture toughness of tungsten carbide

The cobalt-bonded tungsten carbide has been regarded as a specific success in improving the fracture toughness of ceramics. However, the metal binder phase lowers the hardness and corrosion resistance of the composite and limits its applications. In this paper, the possibility of in situ-toughening tungsten carbide, making use of abnormal grain growth of WC grains to reinforce WC-Co composites, is investigated. The volume fraction of abnormally large grains in the samples is controlled by tailoring compositions and sintering conditions. The fracture toughness of the samples is evaluated using the indentation technique. The experiment results show that the fracture toughness of the sample could be improved by introducing a certain volume fraction of abnormal grains, but at some expense of the hardness. The highest value of fracture toughness, 7.34 MPa m0.5, is achieved for WC-0.5 wt% Co-0.25 wt% VC sintered at 2000 °C for 4 h. The main mechanisms for the improved toughness are cutting elongated grains, crack bridging and crack deflection, which could resist crack growth in the sample. Therefore, it is possible to in situ-toughen tungsten carbide using the abnormal grain growth of WC.