Modeling the effect of flatter shape of WC crystals on the hardness of WC-Ni cemented carbides

Hardness of WC-Ni cemented carbides with tiny addition of TiC is studied. The addition of TiC changes the shape of WC crystals to a flatter triangular prism with lower value of the shape equiaxiality P-WC. The hardness increases 8-15% on the alloys with lower value of P-WC. It is shown that none of the existing models for hardness can explain the effect of the shape. A modification to Hall-Petch relation and Lee & Gurland model for hardness is suggested to accommodate the anisotropy and the shape of WC crystals. The mean linear intersections of the carbide and binder phases are multiplied by the normalized shape equiaxiality P-WC/P-WC(0). The modified Lee & Gurland model for anisotropic WC crystals gives a satisfactory fit to the experimental data. in addition, the relationships between fracture toughness and strength vs. hardness for these cemented carbides are presented and discussed. (C) 2008 Elsevier Ltd. All rights reserved.