VC and Cr_3C_2 doped WC-based nano-cermets prepared by MA and SPS

摘要

WC powders with average crystallite size of 10 nm were obtained through planetary ball milling of micron sized WC powder. Nanosized-WC powders were then mechanically milled with both 9 and 12 wt% Co, and the grain growth inhibitors VC and Cr_3C_2 in the range 0.2-0.8 wt%. Powder mixtures were then consolidated using spark plasma sintering (SPS) at two different temperatures, i.e. 1200 and 1300 ℃. The microstructure, densification and mechanical properties of the resulting sintered nano-cermets were analyzed as a function of the type and amount of grain growth inhibitors, Co content, and sintering temperature. In general, the addition of VC and Cr_3C_2 was found to reduce densification. Nevertheless, the effect was found to be lower in Cr_3C_2 containing compositions with higher Co contents. The grain size variation was found by both a conventional line intersection method on FESEM micrographs, and by using grain analyzer software. VC was found to be comparatively more effective in restricting undesirable grain growth during the sintering processes. Moreover, the micro-hardness (H_(V30)) and fracture toughness were measured using micro-indentation and the results were compared for each composition to comparatively assess the individual effect of the inhibitors. Increasing the concentration of inhibitors was found to restrict grain growth even more and higher hardness values were obtained but only up to a critical inhibitor concentration, beyond which the hardness degrades.