Ultrafine Crystal Cemented Carbide Reinforced with Coated Cobalt Powder

Tungsten carbide / cobalt carbide alloys are widely used as cutting tools and die materials because of their high hardness and high wear resistance. The strength and wear resistance of tungsten carbide / cobalt cemented carbide can be significantly improved by decreasing the grain size of WC to ultrafine grain size (1um ~ 100nm) or even nano level (< 100nm). However, in the traditional liquid phase non pressure sintering process, the phenomenon of abnormal growth of ultrafine crystal WC particles is a headache.

How to control the growth of WC has become one of the key technologies for preparing ultrafine grained cemented carbide. At present, ultrafine grained and even nanocrystalline tungsten carbide powders and ultrafine cobalt powders are ball milled to obtain a composite powder. Then, by sintering, obtained ultrafine grain tungsten carbide / cobalt-based cemented carbide. However, the price of ultrafine cobalt powder is very expensive, and during the ball milling process, the ultrafine cobalt powder is easy to oxidize, which makes the ultrafine tungsten carbide / cobalt composite powder after grinding has varying degrees of oxidation problem, and reduces the mechanical properties of the sintered alloy.

Although the use of inflatable protective ball milling method can reduce the oxidation, but due to the use of mechanical milling, ultrafine cobalt powder is mixed evenly, the cobalt powder produced local enrichment, after the completion of the final sintering, cobalt pool phenomenon occurred in the alloy, so that the fracture toughness of the alloy decreases.

Central South University, Song and others proposed a method to prevent the oxidation of cobalt powder to improve the performance of the hardness of the alloy, the main content is based on ultrafine tungsten carbide powder on the current through coating a layer of cobalt salt colloid on the surface and then restored by presintering and hydrogen, finally obtain ultrafine tungsten carbide / cobalt composite powder coated on the surface of nanocrystalline cobalt composite powder, which is suitable for industrialized production.

Compared with the prior art, by coating the surface with cobalt colloid, then pre-calcination decomposition and hydrogen reduction treatment, the obtained ultrafine tungsten carbide / cobalt composite powder has the advantages of uniform distribution of the cobalt powder, small particle size and ultrafine crystalline tungsten carbide particle size remained unchanged. Thus avoiding the uneven distribution and oxidation phenomenon of cobalt powder in ball milling, it also reduces the problem of too long other processes, reduces production cost and energy consumption, and reduces the pollution of CO in tail gas.

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