Effect of Added Cr<sub>3</sub>C<sub>2</sub> on the Microstructure and Mechanical Properties of WC–SiC Ceramics

Abstract

WC–20 mol% SiC ceramics with added Cr3C2 were sintered at 1600°C with a resistance-heated hot-pressing machine. Dense WC–SiC ceramics containing 0.1–0.9 mol% Cr3C2 were obtained. Above 1.2 mol% Cr3C2, the relative density decreased with increasing Cr3C2 content. A small amount of a Nowotny-phase type (Mo5Si3C-type) product was formed by the addition of Cr3C2, and no Cr3C2-based solid solution was found. The WC–20 mol% SiC–Cr3C2 ceramics had very fine equiaxed granular WC grains because of inhibited grain growth of WC. The Young’s modulus of the WC–20 mol% SiC–Cr3C2 ceramics decreased with increasing Cr3C2 content because Cr3C2 has a much lower Young’s modulus than WC. Cr3C2 addition below 0.9 mol% increased the Vickers hardness from 20.9 to 23.0 GPa, but a larger added amount reduced the Vickers hardness. The hardness of the WC–20 mol% SiC–Cr3C2 ceramics and the WC grain size obeyed a Hall–Petch-like relationship, suggesting that the hardness was strongly controlled by the WC grain size. A higher fracture toughness, 6.4 MPa m1/2, was obtained for the ceramics containing a small amount of Cr3C2 than for the binder-free WC. The addition of 0.1–0.3 mol% Cr3C2 improved the fracture toughness without reducing the hardness.