Effects of C and NbC Additions on the Microstructure and Mechanical Properties of Binderless WC Ceramics

Powder mixtures of WC–(0–2 mol%) NbC and WC–1.5 mol% NbC–(0–5 mol%) C were sintered at 1800°C using a resistance-heated hot-pressing machine; dense WC–NbC and WC–1.5 mol% NbC–C ceramics were obtained. The relative X-ray diffraction (XRD) peak intensity of W2Css decreased with increasing C amount and disappeared at 5 mol% C. Small amounts of C remained after sintering at 5 mol% C. The WC–1.5 mol% NbC ceramics with 0–3 mol% of added C were composed of equiaxed small granular grains. Large WC grains formed in WC–1.5 mol% NbC ceramics above 4 mol% C. The hardness of WC–NbC ceramics decreased from 25.7 GPa for WC to 23.6 GPa for 2 mol% NbC obtained by NbC addition. The hardness change for WC–1.5 mol% NbC ceramics with up to 3 mol% of added C was small, around 24 GPa. The Vickers hardness of WC–1.5 mol% NbC ceramics above 4 mol% C decreased markedly from 23 to 13 GPa with increasing added C, due to extensive WC grain growth.