Effects of cobalt additions on WC grain growth

Abstract

Inhomogeneity in the particle size of the tungsten carbide raw material can result in abnormal WC grain growth in WC–Co cemented carbides. For the preparation of ultrafine tungsten carbide powders and ultrafine cemented carbides, abnormal WC grain growth is the most troublesome issue. This paper deals with the effects of cobalt additions on WC grain growth during the carburisation process of nano- and coarse tungsten powders and the sintering process of ultrafine tungsten carbide powders. For the preparation of tungsten carbide powders, it was shown that through the incorporation of 0·035 wt-%Co into W+C mixtures, a dramatic change in WC grain morphology took place for coarse tungsten raw material, while for nanotungsten raw material, a pronounced WC grain growth took place. Plate-like truncated trigonal and hexagonal WC grains were formed during the carburisation process of coarse tungsten raw material containing 0·035 wt-%Co. For the sintering of ultrafine tungsten carbide powders containing 0·3 wt-%Co, an anisotropic and abnormal WC grain growth took place. The mechanisms for WC grain growth were discussed, and suggestions were made for the quality improvement of nano- and ultrafine tungsten carbide powders and ultrafine cemented carbides.

Keywords:

• WC grain
• Grain growth mechanism
• Carburisation
• Sintering
• Ultrafine cemented carbide
• Binderless carbide

Acknowledgements

This project was financially supported by the National Natural Science Foundation of China (grant nos. 51074189 and 50823006), the Science and Technology Planning Project of Hunan Province, China (grant no. 2010FJ2006), the Research Fund for the Doctoral Program of Higher Education of China (grant no. 20100162110001) and the National Science and Technology Special Foundation of China (grant nos. 2009ZX04012-032 and 2011BAE09B02).