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.

Effects of (Ti, W)C Addition on the Microstructure and Mechanical Properties of Ultrafine WC–Co Tool Materials Prepared by Spark Plasma Sintering

“…At 1200 and 1250 °C, WC grains show multi-step structures due to VC and Cr 3 C 2 additions. VC and Cr 3 C 2 additions cause the (W, V, Cr)C x layers to form on the surface of WC grains [7,22,23], which hinders diffusion of W and C atoms and enhances energy barrier for nucleation. The new nucleus and preceding nucleuses grow simultaneously on WC basal planes, causing WC grains to stack on basal planes and to form multi-step structures.…”