Effects of ZrC and SiC addition on the microstructures and mechanical properties of binderless WC

ZrC-added WC ceramics and SiC-added WC-2 mol% ZrC ceramics were sintered at 1800 °C using a resistance-heated hot-pressing machine. Dense WC ceramics containing 0-1 mol% ZrC and WC-2 mol% ZrC ceramics containing 1-6 mol% SiC were obtained. The reaction products W2C, ZrO2 and ZrC-based solid solutions were formed in the ZrC-added WC ceramics during sintering. The relative amount of W2C reached zero at 2 mol% ZrC, increased in the range of 2-6 mol% ZrC, and decreased again above 6 mol% ZrC. The average WC grain size decreased from 0.49 μm for the WC ceramic to 0.24 μm at 4 mol% ZrC. The SiC addition of 1-2 mol% to the WC-2 mol% ZrC ceramics caused abnormal growth of WC grains. The Vickers hardness of the ZrC-added WC ceramics decreased to 17 GPa at 2 mol% ZrC. The hardness of the SiC-added WC-2 mol% ZrC ceramics increased from 12.4 at 2 mol% SiC to 21.5 GPa at 6 mol% SiC. The fracture toughness of the ZrC-added WC ceramics decreased from 6.2 MPa m0.5 for the WC ceramic to 5.2 MPa m0.5 at 4 mol% added ZrC. The fracture toughness of the WC-2 mol% ZrC ceramics with 6 mol% SiC were relatively high at 6.7 MPa m0.5. The addition of SiC to WC-based ceramics thus improved both hardness and fracture toughness.