Nanoscale WC-Co Powder Synthesized Using Ammonium Paratungstate by Co-Precipitation

WC-Co cemented carbides are widely applied in industry which include mining, grinding and metal cutting tools.  Its high hardness and toughness give its widely industrial applications. The microstructural scale is a major to influence its mechanical properties. The hardness can be enhanced by with smaller carbide grain size. The common grain size of WC-Co ranges within l-10 pm.

In the last decade, nanoscale WC-Co powders have been produced by spray conversion process and co-precipitation techniques. The key point to obtain nano scale powders is to create an ideal mixture of the tungsten carbide (WC) and cobalt (Co), with a uniformity of the composition on the nano scale.

Thus, a successful synthesis method of WC-Co (6% Co) cemented carbides using ammonium paratungstate (APT) and cobalt hydroxide as the precursors has been introduced. The experimental procedures are as follows:

A precursor salt consists 66 % W and 4.42 % Co, prepared by co-precipitation using APT and cobalt hydroxide as precursors, was reduced at 600, 650 and 700 °C. The reduction periods were 3 or 6 hrs. Powders reduced at 700 “C were directly carburized at 700 “C during 3 hrs in different mixtures of CO and CO2 (70%CO/30%C02, 80%CO/20%C02, and 90%CO/10%C02).

The samples were heated (S”C/min) up to the reduction temperatures in H2 and left to cool in N2 after reduction or carburization. The total gas flow was about 400 ml/min. The powders were characterized using electron microscopy (SEM, TEM), X-ray diffraction (XRD) and multi - point BET.

In conclusion, the specific surface area of the reduced powders increased with decreasing reduction temperature. The rate of carburization in carbon monoxide - carbon dioxide atmospheres was found to be strongly depending on the ratio carbon monoxide / carbon dioxide. Nanoscale WC-Co powder was synthesized from carburisation at 700 °C. The average particle size obtained from BET- data, was 38 nm at 700 °C, 22 nm at 650 °C and 18 nm at 600 °C.

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