Nano Tungsten Carbide Cobalt Spray Thermal Conversion Method

Tungsten carbide tungsten carbide is a brittle material, its hardness and strength are a pair of contradictions, increasing the hardness of the alloy will lead to the decrease of strength, and on the contrary, the strength of the alloy leads to the decrease of hardness. In recent years, studies have shown that for a WC-Co cemented carbide with a given composition, when the average grain size of the tungsten carbide WC phase decreases below 1 m, the hardness and strength of the hard alloy can not only be increased at the same time, but the increase will increase with the further decrease of the grain size of the WC, so most of the WC-Co nanometers are used at present. Composite powder is used as raw material to prepare superfine cemented carbide.

Recently, with the principle of gas solid reaction, the spray thermal conversion method has been successfully invented in foreign countries. In this method, a mixed solution of tungsten and cobalt is made first, and the tungsten cobalt composite oxide powder is prepared by the technology of atomization drying. Then the oxide powder is reduced by the fluidized bed technology and then carbonized with CO/H₂. Finally, the WC-Co nano composite powder is obtained by using CO/CO₂ for three steps of carbon removal. The details include the following steps:

0.1mol metatungstate, 20mmol cobalt nitrate and 0.1mol citric acid were dissolved in 100ml deionized water and prepared into a clarified mixed solution; complex reaction was performed at 70 centigrade water for 5 hours. The tungsten oxide precursor was obtained by filtration and dried at 120 C for 12 hours; the tungsten oxide precursor was at 700 air atmosphere. The tungsten oxide cobalt oxide powder was obtained by calcining for 1 hours.

The tungsten oxide powder is placed in a tube furnace and nitrided through ammonia gas. The flow rate of ammonia is controlled at 3L/min, the temperature is 750 ℃, the heating rate is 2 /min, and the heat preservation is 3 hours, and the tungsten nitride cobalt nitride powder is obtained.

12 grams of tungsten nitride cobalt nitride powder is mixed with 0.62g carbon black, with ethanol as solvent and tungsten carbide cobalt ball as grinding medium, mixed for 24 hours on roller ball mill, rotary evaporation drying, W₂N/CoN/C mixed powder, W₂N/CoN/C mixed powder in graphite crucible, in a carbon tube furnace, under a vacuum of lower than 200Pa in a carbon tube furnace, will be reversed. The WC-Co nanoparticles were obtained when heated to 1000 ℃ and 3 hours, and the average particle size was 120nm.

The nanoscale tungsten carbide powder prepared by this method is hot pressed at 1200~1400 /1h and 25MPa and the relative density is higher than 97%. It shows that the prepared nano tungsten carbide cobalt powder has good sintering activity, and the raw material is cheap and easy to get. The preparation process is simple and practical, and it can be easily manipulated and easy to realize large-scale production.

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