Effect of Cooling Rate on the Formation and Morphology of (W,V)C x in VC-doped WC–Co Cemented Carbide

Abstract

The grain growth retardation mechanism and the effect of cooling rate on VC-doped WC–Co cemented carbides were investigated in this work. WC–30Co and WC–30Co–VC were prepared by powder metallurgy, liquid-phase sintering at 1400 °C and followed by water quenching (>150 °C/s) or furnace cooling (~0.083 °C/s). Based on the results of electron probe microanalysis (EPMA), we found that WC concentration in the Co binder was independent of VC doping during liquid-phase sintering, hence barely contributing to the retardation of WC grain growth. In contrast, the (W,V)C x phase formed at the WC/Co interfaces played a major role in retarding WC grain growth during liquid-phase sintering. The effect of cooling rate on the morphology of (W,V)C x was revealed by high-resolution transmission electron microscopy (HRTEM) and energy-dispersive spectroscopy (EDS). In the water-quenched WC–30Co–VC, (W,V)C x precipitates were found as thin layers at the WC/Co interfaces. In contrast, both thin layers of similar thickness and nanoparticles of (W,V)C x were observed in the furnace-cooled counterpart. These observations listed above suggested that thin (W,V)C x layers were stable structures effectively suppressing the growth of WC grains and their thickness remained independent of the cooling rate. The (W,V)C x nanoparticles, however, may be inhibited through rapid cooling, ensuring the VC-doped WC–Co cemented carbides desired toughness.